Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry (RSC)  

A high performance for PEC water oxidation results from the formation of a p–n junction at the interface between CoPi and α-Fe₂O₃, which is first observed among the hitherto-reported α-Fe₂O₃/CoPi-based electrodes.

DOI： 10.1039/d3se00346a

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Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/acs.inorgchem.2c01937

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Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/acsaem.2c00768

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Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/acsami.1c24263

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Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.fuel.2021.122954

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Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/acsaem.1c03379

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Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry (RSC)  

Pt nanoparticles stabilized by a polymeric stabilizer of polyacrylic acid were stably adsorbed on an ITO electrode to work effectively and stably for electrocatalytic proton reduction.

DOI： 10.1039/d1se01760h

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Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry (RSC)  

A Pt cathode (Pt(w-MeIm)) prepared by a mixed metal-imidazole casting (MiMIC) method showed a remarkably superior hydrogen evolution reaction (HER) performance compared to the cathode prepared without imidazole (Pt(w/o-MeIm)), and the common Pt-based benchmark cathodes of Pt/C or the Pt plate.

DOI： 10.1039/d2se00803c

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Publishing type：Research paper (scientific journal)   Publisher：Proceedings of the National Academy of Sciences  

The understanding of O–O bond formation is of great importance for revealing the mechanism of water oxidation in photosynthesis and for developing efficient catalysts for water oxidation in artificial photosynthesis. The chemical oxidation of the Ru^II₂(OH)(OH₂) core with the vicinal OH and OH₂ ligands was spectroscopically and theoretically investigated to provide a mechanistic insight into the O–O bond formation in the core. We demonstrate O–O bond formation at the low-valent Ru^III₂(OH) core with the vicinal OH ligands to form the Ru^II₂(μ-OOH) core with a μ-OOH bridge. The O–O bond formation is induced by deprotonation of one of the OH ligands of Ru^III₂(OH)₂ via intramolecular coupling of the OH and deprotonated O⁻ ligands, conjugated with two-electron transfer from two Ru^III centers to their ligands. The intersystem crossing between singlet and triple states of Ru^II₂(μ-OOH) is easily switched by exchange of H⁺ between the μ-OOH bridge and the auxiliary backbone ligand.

DOI： 10.1073/pnas.2113910118

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Publishing type：Part of collection (book)   Publisher：IntechOpen  

Polypyridyl ruthenium(II) complexes have been widely researched as promising functional molecules. We have found unique photoisomerization reactions of polypyridyl ruthenium(II) aquo complexes. Recently we have attempted to provide insight into the mechanism of the photoisomerization of the complexes and distinguish between the distal−/proximal-isomers in their physicochemical properties and functions. Moreover, polypyridyl ruthenium(II) aquo complexes have been intensively studied as active water oxidation catalysts (WOCs) which are indispensable for artificial photosynthesis. The catalytic aspect and mechanism of water oxidation by the distal-/proximal-isomers of polypyridyl ruthenium(II) aquo complexes have been investigated to provide the guided thought to develop more efficient molecular catalysts for water oxidation. The recent progress on the photoisomerization and water oxidation of polypyridyl ruthenium(II) aquo complexes in our group are reviewed to understand the properties and functions of ruthenium complexes.

DOI： 10.5772/intechopen.99730

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Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/acsami.1c08949

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Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/acsaem.0c03125

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Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.electacta.2021.138545

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Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/acsaem.1c00261

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Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/acsaem.0c02628

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Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry (RSC)  

<p>Electrocatalytic water splitting to oxygen and hydrogen has much attention as one of the most promising approaches for sustainable production of hydrogen as a carbon-neutral fuel. To establish efficient electrocatalytic...</p>

DOI： 10.1039/d1ee00509j

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Publishing type：Research paper (scientific journal)   Publisher：The Electrochemical Society  

DOI： 10.1149/1945-7111/abd3ba

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Other Link： https://iopscience.iop.org/article/10.1149/1945-7111/abd3ba/pdf

Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/acsaem.0c02242

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Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/acsaem.0c01439

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Publishing type：Research paper (scientific journal)  

© 2020 A mononuclear Ru aquo complex, [Ru(C8Otpy)(H2dcbpy)(OH2)]2+ (C8Otpy = 4′-octyloxy-2,2′:6′,2′′-terpyridine, H2dcbpy = 4,4′-dicarboxy-2,2′-bipyridine) was stably adsorbed on a nanoporous TiO2 surface to afford a TiO2 electrode anchoring the complex. The adsorption isothermal of the complex on the TiO2 surface was analyzed by the Langmuir adsorption model to provide a maximum coverage of Гmax = 4.4 × 10−8 mol cm−2 and an adsorption equilibrium constant of Kads = 1.1 × 104 M−1, suggesting that the monolayer of the complex is formed on the TiO2 surface. The cyclic voltammetry measurement of the complex on the TiO2 surface suggested the diffusion-controlled charge transport via electron hopping between the complexes through the TiO2 layer. Pourbaix diagram showed that the complex undergoes a non-H+-coupled 1e- redox reaction of a RuIIOH/RuIIIOH pair of the complex on the TiO2 electrode due to pH buffering ability of the TiO2 surface in a range of pH 5−11. Bulk electrolysis at 1.7 V vs Ag/AgCl using the complex-anchoring TiO2 electrode provided a high and steady catalytic current density of 0.39 mA cm−2 with 83 % Faradaic efficiency for O2 evolution during 1 h electrolysis. However, we presume that the complex is transformed to RuOx nanoparticles on the TiO2 electrode during the electrocatalysis, on the basis of our earlier report on the complex / mesoporous ITO electrode system (Dalton Trans., 2020, 49, 1416−1423.). The RuOH/TiO2 electrode is the efficient anode for water oxidation under the acidic conditions, irrespective of the molecular catalyst of RuOH and the alternative catalysts formed via its oxidative transformation.

DOI： 10.1016/j.jphotochem.2020.112696

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

A non-heme Fe complex with a tetradentate dicarboxamide N-4 in-plane ligand works efficiently and selectively for the electrocatalytic CO2-to-CO conversion in a homogeneous DMF solution. The complex was immobilized on a nitrogen-doped graphene (N-G) to achieve a CO2-to-CO conversion in neutral aqueous NaHCO3 solutions, affording CO with Faradaic efficiency of 90%, a current density of 6 mA cm(-2), and a turnover frequency of 2.1 s(-1), at an overpotential of 0.47 V, which is among those of the hitherto-reported efficient and selective Fe complexes electrocatalysts.

DOI： 10.1021/acsaem.9b02548

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Language：English  

A new mononuclear Ru aquo complex [Ru(C8Otpy)(H2dcbpy)(OH2)]2+ with 4,4'-dicarboxy-2,2'-bipyridine (H2dcbpy) and 4'-octyloxy-2,2':6',2''-terpyridine (C8Otpy) ligands was synthesized to investigate electrocatalytic water oxidation by the complex immobilized on a mesoporous indium-doped tin oxide (meso-ITO) electrode using a multi-potential-step chronocoulospectrometric (MPSCCS) technique. UV-visible absorption spectroscopic data indicated that [Ru(C8Otpy)(dcbpy)(OH2)] (RuOH2) is deprotonated to [Ru(C8Otpy)(dcbpy)(OH)]- (RuOH) on the meso-ITO surface even at pH 5.9 of the electrolyte solution. The cyclic voltammogram (CV) of the RuOH/meso-ITO electrode showed a pH-independent redox response at E1/2 = 0.80 V vs. Ag/AgCl in the pH range of 5-12, being assigned to a non-proton-coupled 1e- redox process of RuIIOH/RuIIIOH. The MPSCCS measurement of the RuOH/meso-ITO electrode between 0.2 and 1.5 V vs. Ag/AgCl showed that RuIV species (tentatively RuIVO) exist in a steady state of the electrocatalysis in the initial stage. This suggests that the electrochemical oxidation from RuIVO to RuVO could compete with the water nucleophilic attack for O-O bond formation involved in the rate-determining step under the employed conditions. The possibility that the water nucleophilic attack on RuIVO could also compete with the electrochemical oxidation of RuIVO to RuVO was suggested by the electrocatalytic water oxidation at a low applied potential of 1.4 V prior to the formation potential of RuVO. The MPSCCS measurement at 1.4 V for 1 h showed that RuOH is gradually transformed into an alternative catalyst (most likely RuOx nanoparticles) on the electrode. The MPSCCS technique is promising to reveal the redox reactions and catalytic aspects of molecular catalysts immobilized on an electrode for water oxidation.

DOI： 10.1039/c9dt04442f

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Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry (RSC)  

<p>A ruthenium complex showing multi-stimuli-responsive isomerization was synthesized.</p>

DOI： 10.1039/d0cc04940a

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Nanorod architecture of a N-2-intercalated WO3 photoanode has been developed by emphasizing the dual role of N2H4, which functioned simultaneously as a structure-directing agent and as a nitrogen source for in situ N-2 intercalation. The N content for WO3-N2H4 increased with increase of calcination temperature from 350 to 420 degrees C and thereafter decreased up to 550 degrees C. This is different from the monotonously decreased N content with the calcination temperature increase for WO3-NH3. X-ray diffraction data indicated that the phase-pure monoclinic WO3 crystals are formed over 350 degrees C calcination for WO3-N2H4, in contrast to a mixed phase of hexagonal and monoclinic WO3 crystals below 500 degrees C for WO3-NH3. The crystallinity of the monoclinic phase for WO3-N2H4 is higher than those of WO3-neat and WO3-NH3 at each calcination temperature of 350-550 degrees C. The beta values of lattice parameters of the monoclinic phase changed significantly with the calcination temperature; this is consistent with the calcination temperature dependence of the N content, clarifying the intercalation of N-2 in the WO3 lattice. The UV-visible diffuse reflectance spectra of WO3-N2H4 exhibited a shoulder at 470-630 nm, which became more intense as the calcination temperature increased from 350 degrees C and then decreased up to 550 degrees C through the maximum at 420 degrees C. This temperature dependence is consistent with the cases of the N content and the lattice parameter of beta. This indicates that N-2 intercalation into the WO3 lattice is responsible for the considerable red shift in the absorption edge, with a new shoulder appearing at 470-630 nm due to transition from a new intermediate N 2p orbital formed in the conduction band of WO3. Based on this transition, the WO3-N2H4 photoanode can utilize the visible light in longer wavelength below 520 nm for photoelectrochemical water oxidation compared to 470 nm for WO3-neat. The high incident photon-to-current conversion efficiency of the WO3-N2H4 photoanode is due to efficient electron transport through the WO3 nanorod film.

DOI： 10.1021/acssuschemeng.9b04467

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DOI： 10.1021/acs.inorgchem.9b01623

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/cssc.201802795

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Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.energy.2019.02.072

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Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry (RSC)  

<p>A new transparent mesoporous IrOx film consisting of small interconnected nanoparticles has been developed by a simple drop-cast method to provide an efficient electrocatalyst film for water oxidation.</p>

DOI： 10.1039/c9se00731h

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier B.V.  

The hexagonal-shaped β-Co(OH)2 discs were electrophoretically deposited on an electrode to yield a stably adherent and uniform β-Co(OH)2 layer. The electrocatalytic water oxidation at the β-Co(OH)2 layer-deposited electrode was investigated to seek efficient water oxidation catalyst for artificial photosynthesis as promising energy-providing systems for the future. The β-Co(OH)2 layer did not work as a water oxidation catalyst in a K2SO4 solution at pH 7.0 when applying 1.70 V vs. reversible hydrogen electrode (RHE), although the layer was oxidized to the CoO(OH) layer. In a phosphate buffer solution (pH 7.0), the β-Co(OH)2 layer was dissolved and oxidatively re-deposited as the Co-Pi catalyst (Science, 321 (2008) 1072–1075.) when applying the same potential. While in a Na2B4O7 solution at pH 9.4, the β-Co(OH)2 layer was oxidized to the CoO(OH) layer with the hexagonal-disc-shape remained when applying 1.7 V vs. RHE, and the formed CoO(OH) layer works efficiently for electrocatalytic water oxidation in contrast to no catalytic activity in a K2SO4 solution at pH 9.4. The catalytic performance of the formed CoO(OH) layer was evaluated
the overpotential (η) of 0.42 V for current generation of 100 μA cm−2 and the Tafel slope of 0.21 ∼ 0.29 V dec−1 were provided for water oxidation at pH 9.4, which are comparable with efficient cobalt-based catalyst films reported so far.

DOI： 10.1016/j.jphotochem.2017.09.052

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley-VCH Verlag  

With a view to developing a photoanode for visible light-driven water oxidation in solar water splitting cells, pure-monoclinic WO3 nanorod crystals with N2 intercalated into the lattice were synthesized by using hydrazine with a dual functional role—as an N atom source for the in situ N2 intercalation and as a structure-directing agent for the nanorod architecture—to gain higher incident photon-to-current conversion efficiency at 420 nm than with most previously reported WO3 electrodes.

DOI： 10.1002/cssc.201702439

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Publishing type：Research paper (scientific journal)   Publisher：Wiley  

DOI： 10.1002/cssc.201800593

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Publishing type：Research paper (scientific journal)   Publisher：Wiley  

DOI： 10.1002/cptc.201700200

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

The synthesis of silver nanoparticles (AgNPs) within the interlayer space of transparent layered titania nanosheet (TNS) films is investigated. A considerable number of silver ions (approximate to 70% against the cation exchange capacity of the TNS) are intercalated in the TNS films using methyl-viologen-containing TNSs as a precursor. The silver ion (Ag+)-containing TNS films are treated with aqueous sodium tetrahydroborate (NaBH4), resulting in a gradual color change to bright blue. Various structural analyses clearly show that crystalline AgNPs are generated within the interlayer space of the TNSs. The NaBH4-treated films show intense and characteristic near-infrared (NIR) extinction spectra up to 1800 nm. The tability of the AgNPs within the TNS against oxygen and moisture is also investigated, and 96% and 82% of the AgNPs remain after standing in air for 1 month and 1 year, respectively. The NIR extinctions of the AgNP-containing TNS films are further extended by employing different preparation procedures, for example, using sintered TNS films as starting materials and irradiating the Ag+-containing TNSs with ultraviolet (UV) light. The obtained AgNP-containing TNS films exhibit photochemical activities in the production of hydrogen from ammonia borane under visible-light irradiation and the decomposition of nitrogen monoxide under UV-light irradiation.

DOI： 10.1002/gch2.201700105

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Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/acssuschemeng.8b04166

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

A heterogeneous catalyst incorporating an inorganic ion cofactor for electrochemical water oxidation was exploited using a CoO(OH) nanoparticle layer-deposited electrode. The significant catalytic current for water oxidation was generated in a Na2B4O7 solution at pH 9.4 when applying 0.94 V versus Ag/AgC1 in contrast to no catalytic current generation in the K2SO4 solution at the same pH. HB4O7 and B4O72- ions were indicated to act as key cofactors for the induced catalytic activity of the CoO(OH) layer. The Na2B4O7 concentration dependence of the catalytic current was analyzed based on a Michaelis-Menten-type kinetics to provide an affinity constant of cofactors to the active sites, K-m = 28 +/- 3.6 mM, and the maximum catalytic current density, I-max = 2.3 +/- 0.13 mA cm(-2). The I-max value of HB4O7- and B4O72- ions was 1.4 times higher than that (1.3 mA cm(-2)) for the previously reported case of CO32- ions. This could be explained by the shorter-range proton transfer from the active site to the proton-accepting cofactor because of the larger size and more flexible conformation of HB4O7 and B(4)O(7)(2-)ions compared with that of CO32- ions.

DOI： 10.1021/acsami.7b13817

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

proximal,proximal-(p,p)-[Ru-2(II)(tpy)(2)LXY](n+) (tpy = 2,2';6',2 ''-terpyridine, L = 5-phenyl-2,8-di-2-pyridyl-1,9,10-anthyridine, and X and Y = other coordination sites) yields the structurally and functionally unusual Ru-II(mu-OH)Ru-II core, which is capable of catalyzing water oxidation with key water insertion to the core (Inorg. Chem. 2015, 54, 7627). Herein, we studied a sequence of bridging-ligand substitution among p,p-[Ru-2(tpy)(2)L(mu-Cl)](3+) (RU2(mu-Cl)), p,p-[Ru-2(tpy)(2)L(mu-OH)](3+) (Ru-2(mu-OH)), p,p-[Ru-2(tpy)(2)L-(OH)(OH2)](3+) (Ru-2(OH)(OH2)), and p,p-[Ru-2(tpy)(2)L-(OH)(2)](2+) (Ru-2(OH)(2)) in aqueous solution. Ru-2(mu-Cl) converted slowly (10(-4) s(-1)) to Ru-2(mu-OH), and further Ru-2(mu-OH) converted very slowly (10(-6) s(-1)) to Ru-2(OH)-(OH2) by the insertion of water to reach equilibrium at pH 8.5-12.3. On the basis of density functional theory (DFT) calculations, Ru-2(OH)(OH2) was predicted to be thermodynamically stable by 13.3 kJ mol(-1) in water compared to Ru-2(mu-OH) because of the specially stabilized core structure by multiple hydrogen-bonding interactions involving aquo, hydroxo, and L backbone ligands. The observed rate from Ru-2(mu-OH) to Ru-2(OH)(2) by the insertion of an OH- ion increased linearly with an increase in the OH- concentration from 10 to 100 mM. The water insertion to the core is very slow (similar to 10(-6) s(-1)) in aqueous solution at pH 8.5-12.3, whereas the insertion of OH- ions is accelerated (10(-5)-10(-4) s(-1)) above pH 13.4 by 2 orders of magnitude. The kinetic data including activation parameters suggest that the associative mechanism for the insertion of water to the Ru-II(mu-OH)Ru-II core of Ru-2(mu-OH) at pH 8.5-12.3 alters the interchange mechanism for the insertion of an OH- ion to the core above pH 13.4 because of relatively stronger nucleophilic attack of OH- ions. The hypothesized p,p-[Ru-2(tpy)(2)L(mu-OH2)](4+) and p,p-[Ru-2(tpy)(2)L(OH2)(2)](4+) formed by protonation from Ru-2(mu-OH) and Ru-2(OH)(OH2) were predicted to be unstable by 71.3 and 112.4 kJ mol(-1) compared to Ru-2(mu-OH) and Ru-2(OH)(OH2), respectively. The reverse reactions of Ru-2(mu-OH), Ru-2(OH)(OH2), and Ru-2(OH)(2) to Ru-2(mu-Cl) below pH 5 could be caused by lowering the core charge by protonation of the mu-OH- or OH- ligand.

DOI： 10.1021/acs.inorgchem.7b00978

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

Semiconductor nanowires with both nano- and micrometre dimensions have been used as effective materials for artificial photosynthesis; however, a single synthesis approach to provide rational control over the macroscopic morphology, which can allow for the high-throughput screening of photocatalytic performance, and carrier transfer between oxide and sulphide nanostructures has been poorly known. Our recent findings indicate that a single parameter, Nb foil thickness, in a vapor-phase synthesis method can alter the macroscopic morphology of resulting Nb2O5 nanowires. Thick Nb foil results in a free-standing Nb2O5 film, whereas a thinner foil leads to fragmentation to give a powder. During the synthesis process, a Rh dopant was provided through metal-organic chemical vapor deposition to reduce the Nb2O5 energy gap. Upon irradiation with visible light (lambda &gt; 440 nm), the free-standing nanowire film [Nb2O5: Rh-NW(F)] showed photoanodic current with a Faradaic efficiency of 99% for O-2 evolution. Under identical irradiation conditions, the powdered counterpart [Nb2O5: Rh-NW(P)] showed activity for O-2 evolution in the presence of an electron acceptor. The poor water-reduction ability was greatly enhanced by the Au-catalysed vapor-liquid-solid (VLS) growth of H-2-evolving CdS onto the reduction sites of Nb2O5: Rh-NW(P) [Au/CdS/Nb2O5: Rh-NW(P)].

DOI： 10.1038/s41598-017-05292-2

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Transparent IrOx catalyst films for water oxidation were fabricated on fluorine-doped tin oxide electrodes from Ir precursor complex solutions containing Pluronic P123, Brij 58 or Pluronic F127 as surfactant structure directing agents (SDAs). The thin layers composed of highly dispersed and very small nanoparticles of ca. &lt;= 2 nm were formed for IrOx films derived by Pluronic P123 and Brij 58, both of which act as a 'spacer' between the Ir-building-blocks to inhibit further agglomeration of the nanoparticles. Pluronic F127 with relatively longer hydrophilic poly(ethylene oxide) blocks stabilizes Ir-complexes in the precursor solution due to stronger interaction between its longer ED-units and Ir-complexes, affording the organized mesoporous structures of ca. 8 nm pores templated by micelles formed in the IrOx film derived by Pluronic F127. The cyclic voltammetry revealed the catalytic currents for water oxidation for the SDAs-derived IrOx films were 1.3-1.8 times higher than the IrO, film without SDA. The higher water oxidation activity observed is attributed to the higher intrinsic catalytic activity of Ir-sites on very small nanoparticles in the Pluronic P123 and Brij 58-derived IrOx films, whereas it is attributed to the increased number of active Ir-sites due to the organized mesoporous structures of the Pluronic F127-derived IrOx film. (C) 2017 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.cattod.2017.03.009

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Language：English   Publisher：ROYAL SOC CHEMISTRY  

DOI： 10.1039/c7fd90017a

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

N-2-Intercalated crystalline mesoporous tungsten trioxide (WO3) was synthesized by a thermal decomposition technique with dodecylamine (DDA) as a surfactant template with a dual role as an N-atom source for N-2 intercalation, alongside its conventional structure-directing role (by micelle formation) to induce a mesoporous structure. N-2 physisorption analysis showed that the specific surface area (57.3m(2)g(-1)) of WO3 templated with DDA (WO3-DDA) is 2.3 times higher than that of 24.5m(2)g(-1) for WO3 prepared without DDA (WO3-bulk), due to the mesoporous structure of WO3-DDA. The Raman and X-ray photoelectron spectra of WO3-DDA indicated intercalation of N-2 into the WO3 lattice above 450 degrees C. The UV/Vis diffuse-reflectance spectra exhibited a significant shift of the absorption edge by 28nm, from 459nm (2.70eV) to 487nm (2.54eV), due to N-2 intercalation. This could be explained by the bandgap narrowing of WO3-DDA by formation of a new intermediate N 2p orbital between the conduction and valance bands of WO3. A WO3-DDA-coated indium tin oxide (ITO) electrode calcined at 450 degrees C generated a photoanodic current under visible-light irradiation below 490nm due to photoelectrochemical water oxidation, as opposed to below 470nm for ITO/WO3-bulk. The incident photon-to-current conversion efficiency (IPCE=24.5%) at 420nm and 0.5V versus Ag/AgCl was higher than that of 2.5% for ITO/WO3-bulk by one order of magnitude due to N-2 intercalation and the mesoporous structure of WO3-DDA.

DOI： 10.1002/chem.201700088

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

A novel type of energy donor-acceptor system on a clay surface has been prepared. The energy transfer between an energy-donating cationic pyrene derivative (An-Py2+) and an energy-accepting tris(bipyridine)ruthenium complex (Ru2+) on the clay surface was investigated using absorption, emission, and lifetime measurements. An obvious energy transfer was observed, and one Ru2+ molecule quenched the emission from five molecules of An-Py2+ with an emission quenching efficiency of 85% on the clay surface. This suggests that the light energies absorbed by five of the An-Py2+ molecules were accumulated in the one Ru2+ molecule. Near-quantitative emission quenching was observed for stoichiometric amounts of An-Py2+ and Ru2+. The apparent quenching rate constant is approximately 10(17) L mol(-1) s(-1), and thus the quenching rate constant is 10(7)-10(8) times higher than the diffusion rate constant in a homogeneous solution.

DOI： 10.1021/acs.langmuir.7b00512

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

Ruthenium(II) complexes with polypyridyl ligands have been extensively studied as promising functional molecules due to their unique photochemical and photophysical properties as well as redox properties. In this context, we report the photoisomerization of distal-[Ru(tpy)(pynp)OH2](2+) (d-1) (tpy = 2,2'; 6',2'' terpyridine, pynp = 2-(2-pyridyl)-1,8-naphthyridine) to proximal-[Ru(tpy)(pynp)OH2](2+) (p-1), which has not been previously characterized for polypyridyl ruthenium(II) aquo complexes. Herein, we review recent progress made by our group on the mechanistic insights and application developments related to the photoisomerization of polypyridyl ruthenium(II) aquo complexes. We report a new strategic synthesis of dinuclear ruthenium(II) complexes that can act as an active water oxidation catalyst, as well as the development of unique visible-light-responsive giant vesicles, both of which were achieved based on photoisomerization.

DOI： 10.1039/c7dt00079k

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

A novel type of trimethylanilinium-substituted pyrene derivative, 1,6-di(N,N,N-trimethylanilinium-4-y1) pyrene 2I(-)(An-Py2+), was synthesized. An-Py2+ exhibits strong emission with a high-emission quantum yield (approximately 90%) in aqueous solution. An-Py2+ was hybridized on a clay (Sumecton SA (SSA)) surface, and the photochemical behavior of An-Py2+ on the SSA surface was investigated using absorption and emission spectroscopic analyses, emission quantum yield (Phi(f)), and lifetime (tau) measurements. Effective adsorption of An-Py2+ on SSA was observed, and adsorption limit was estimated to be 100% relative to the cation-exchange capacity (CEC) of SSA. The previously reported pyridinium-substituted pyrene derivatives cause a gradual redshift of both absorption and emission on the SSA surface. In contrast, An-Py2+ effectively suppresses such a redshift on SSA due to anilinium substitution of the pyrene unit. (C) 2017 Elsevier B.V. All rights reserved.

DOI： 10.1016/jjphotochem.2017.01.023

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

Synthetic models of oxygen evolving complex (OEC) are used not only to gain better understanding of the mechanism and the roles of cofactors for water oxidation in photosynthesis, but also as water oxidation catalysts to realize artificial photosynthesis, which is anticipated as a promising solar fuel production system. However, although much attention has been paid to the composition and structure of active sites for development of heterogeneous OEC models, the cofactors, which are essential for water oxidation by the photosynthetic OEC, remain little studied. The high activity of CoO(OH) nanoparticles for electrocatalytic water oxidation is shown to be induced by a CO32- cofactor. The possibility of CO32- ions acting as proton acceptors for O-O bond formation based on the proton-concerted oxygen atom transfer mechanism is proposed. The O-O bond formation is supposed to be accelerated due to effective proton acceptance by adjacent CO32- ions coordinated on the CoIV center in the intermediate, which is consistent with Michaelis-Menten-type kinetics and the significant H/D isotope effect observed in electrocatalysis.

DOI： 10.1002/cssc.201601494

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JOURNAL OF VISUALIZED EXPERIMENTS  

Combinations of metal oxide semiconductors and gold nanoparticles (AuNPs) have been investigated as new types of materials. The in situ synthesis of AuNPs within the interlayer space of semiconducting layered titania nanosheet (TNS) films was investigated here. Two types of intermediate films (i.e., TNS films containing methyl viologen (TNS/MV2+) and 2-ammoniumethanethiol (TNS/2-AET(+))) were prepared. The two intermediate films were soaked in an aqueous tetrachloroauric(III) acid (HAuCl4) solution, whereby considerable amounts of Au(III) species were accommodated within the interlayer spaces of the TNS films. The two types of obtained films were then soaked in an aqueous sodium tetrahydroborate (NaBH4) solution, whereupon the color of the films immediately changed from colorless to purple, suggesting the formation of AuNPs within the TNS interlayer. When only TNS/MV2+ was used as the intermediate film, the color of the film gradually changed from metallic purple to dusty purple within 30 min, suggesting that aggregation of AuNPs had occurred. In contrast, this color change was suppressed by using the TNS/2-AET(+) intermediate film, and the AuNPs were stabilized for over 4 months, as evidenced by the characteristic extinction (absorption and scattering) band from the AuNPs.

DOI： 10.3791/55169

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

Polychromium-oxo-deposited TiO2 ((CrxOy)-O-III/TiO2) electrodes were fabricated by a simple electrochemical technique by using different TiO2 basal electrodes (anatase, rutile, and mixed polymorphic phases P25) as earth-abundant photoanodes for visible-light-driven water oxidation. The high-resolution transmission electron microscopy (HR-TEM) observation illustrated that an (CrxOy)-O-III layer with approximately 2-3nm thickness was formed on the surface of the crystalline TiO2 particles. Upon visible-light irradiation of the electrodes, the photoanodic current based on water oxidation was generated at the (CrxOy)-O-III/TiO2 electrodes. However, the wavelength (below 620nm) for photocurrent generation at (CrxOy)-O-III/TiO2-rutile was longer than that (below 560nm) at (CrxOy)-O-III/TiO2-P25 by 60nm, which is in agreement with the difference (0.2eV) in the conduction band (CB) edge energy between rutile and anatase TiO2. This gives a quantitative account for the photocurrent generation based on interfacial charge transfer (IFCT) from Cr3d of the deposited (CrxOy)-O-III layer to the TiO2 CB. The photocurrent generated for (CrxOy)-O-III/TiO2-rutile was higher than that for (CrxOy)-O-III/TiO2-anatase, which is ascribed to 1)more effective (CrxOy)-O-III deposition on the rutile particles, 2)a larger electrolyte/(CrxOy)-O-III interface for water oxidation as a result of smaller rutile particles (ca. 30-40nm) compared with larger P25 particles (ca. 40-80nm), and 3)more effective use of visible light owing to the low energy IFCT transition of rutile.

DOI： 10.1002/cplu.201600288

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

A new transparent iridium oxide (IrOx) film on fluorine-doped tin oxide (FTO) electrodes were achieved from a homogeneous precursor complex solution by employing a facile spin-coating technique. The composition of the nanostructure and crystallinity of the IrOx film is tunable by a simple annealing treatment of a compact complex layer, which is responsible for their significantly different electrocatalytic performances for water oxidation. Transmission electron microscopy (TEM) observations showed uniformly dispersed small IrOx nanoparticles of dimensions ca. 2-5 nm for the film annealed at 300 degrees C, and the nanoparticles gradually agglomerated to form relatively large particles at higher temperatures (400 and 500 degrees C). The IrOx films prepared at different annealing temperatures are characterized by Raman spectroscopic data to reveal intermediate IrOx(OH)(y) nanoparticles with two oxygen binding motifs: terminal hydroxo and bridging oxo at 300 and 350 degrees C annealing, via amorphous IrOx at 400 degrees C, transforming ultimately to crystalline IrO2 nanoparticles at 500 degrees C. Cyclic voltammetry suggests that the intrinsic activity of catalytic Ir sites in intermediate IrOx(OH)(y) nanoparticles formed at 300 degrees C annealing is higher in comparison with amorphous and crystalline IrOx nanoparticles. Electrochemical impedance data showed that the charge transfer resistance (R-ct = 232 Omega) for the IrOx(OH)(y) film annealed at 300 degrees C is lower relative to that of films annealed at higher temperatures. This is ascribable to the facilitated electron transfer in grain boundaries between smaller IrOx particles to lead the efficient electron transport in the film. The high intrinsic activity of catalytic Ir sites and efficient electron transport are responsible for the high electrocatalytic performance observed for the intermediate IrOx(OH)(y) film annealed at 300 degrees C; it provides the lowest overpotential (eta) of 0.24 V and Tafel slope of 42 mV dec(-1) for water oxidation at neutral pH, which are comparable with values for amorphous IrOx center dot nH(2)O nanoparticle films (40-50 mV dec(-1)) reported as some of the most efficient electrocatalysts so far.

DOI： 10.1021/acscatal.6b00621

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

Visible- and red-light responsive vesicles were prepared by incorporating a ruthenium aqua complex having two alkyl chains on tridentate and asymmetrical bidentate ligands (proximal-2: [Ru(C(10)tpy)(C(10)pyqu)OH2](2+), C(10)tpy=4-decyloxy-2,2;6,2-terpyridine, C(10)pyqu=2-[2-(6-decyloxy)-pyridyl]quinoline). The ruthenium complex of proximal-2 with closed alkyl chain geometry and a cylinder-like molecular shape exhibited photoisomerization to distal-2 with an open alkyl chain geometry and a cone-like shape, both in an aqueous solution and in vesicle dispersions. We observed that light irradiation of giant vesicles containing proximal-2 induced diverse morphological changes.

DOI： 10.1002/chem.201504249

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

C-60 fullerene derivatives, which are formed by grafting polymer chains on a C-60 fullerene, can improve the solubility of C-60 in solvents. These derivatives are able to composite with various functional polymers to form interpenetrating network gel structures. In this study, a composite gel composed of the C-60 fullerene derivatives and poly(3,4-ethylenedioxythiophene)(PEDOT) was prepared using a low-temperature organic-solvent process, and its photoelectric properties were evaluated. Furthermore, the poly(ethylene glycol) (PEG) radicals were successfully trapped in the fullerene (C-60), which worked as a cross-linking point to yield the C-60-PEG gel. Then, PEDOT was composited with the gel using chemical oxidative polymerization to form the C-60-PEG/PEDOT gel. The structure of the film prepared using this composite material was identified. The C-60-PEG/PEDOT film had an amorphous network structure and the UV response was much higher than that of the C-60-PEG gel. In addition, it was estimated that PEDOT was synthesized inside the C-60-PEG gel and formed nanoscale junctions between C-60 and PEDOT, which was beneficial for the movement of electrons and holes. The photocurrent was observed by irradiating the C-60-PEG/PEDOT gel electrode with UV or simulated sunlight. The power conversion efficiency (PCE) was calculated as 1.2 x 10(-3)%. Therefore, it is expected that the C-60-PEG/PEDOT material is applicable for the photoelectric field, such as solar cells.

DOI： 10.1038/pj.2015.65

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

We report the first in situ synthesis of copper nanoparticles (CuNPs) within the interlayer space of inorganic layered semiconductors (titania nanosheet films) through the following steps. A sintered titania nanosheet (s-TNS) film was synthesised, forming a transparent, layered semiconductor film (similar to 2 mu m thick). A considerable amount of copper ions (ca. 68% relative to the cation exchange capacity of TNSs) was intercalated in the s-TNSs using the methyl viologen-containing s-TNSs as the intermediate. The resultant copper-containing s-TNS (TNS/Cu2+) film was treated with an aqueous solution of NaBH4, resulting in a colour change. Extinction spectra of NaBH4-treated films exhibited a wide extinction band at lambda(max) (the extinction band maximum) = 683 nm. The spectral shapes and lambda(max) were similar to those for copper nanoparticles on TiO2 surfaces. Transmission electron microscopy analysis demonstrated the wide distribution of electron dense particles on the titania sheet of NaBH4-treated TNS/Cu2+. XRD analysis and absorption/extinction analysis with different amounts of TNSs suggest that CuNPs were formed within the interlayer space rather than the surface of TNSs through NaBH4 treatment. Repeatable oxidation and reduction behaviour, i.e. colouration and decolouration cycles of the copper species within TNS films, was investigated.

DOI： 10.1039/c5tc03152d

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

Electrochemical water oxidation by [Ru(EtOtpy)(bpy)OH2](2+) (1) (EtOtpy =4'-ethoxy-2,2':6'2 ''-terpyridine, bpy = 2,2'-bipydidine) was investigated in a homogeneous solution under weakly acidic conditions (pH 5.3). The cyclic voltammogram of a 1 aqueous solution showed that successive proton-coupled electron transfer reactions of Ru-II-OH2 Ru-III-OH and Ru-III-OH/Ru-IV=O redox pairs and high anodic current above 1.1 V vs SCE. Electrocatalytic water oxidation was corroborated by the bulk electrolysis at 1.5 V; the significant amount of O-2 was evolved compared with the blank during the electrolysis. Potential-step chronocoulospectrometry (PSCCS) from 0.0 V to 1.52 V vs SCE was conducted to observe the change of 1 in solution during the electrocatalysis. The in situ UV visible spectral change showed oxidation of I (Ru-II-OH2) to Ru-III-OH and to further oxidation of Ru-III-OH to Ru-IV=O, and that the Ru-IV=O species mainly exists in a steady state after 200 s in the electrocatalysis. The in situ UV-vis spectral change in a reverse potential step from 1.52V to 0.22V vs SCE exhibited that Ru-II-OH2 completely recovers by two electron re-reduction process from the steady state in the electrocatalysis. The observation of Ru-IV=O in a steady state suggests that a rate determining step in the catalytic cycle is oxidation of Ru-IV=O to Ru-V=O rather than the O-O bonding formation by nucleophilic attack of water to Ru-V=O in the electrocatalysis in a homogeneous solution. (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jphotochem.2015.06.010

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

The quasi-stable excited states of distal- and proximaliRu(tpy)(pynp)OH2](2+) (tpy = 2,2',6',2 ''-terpyridine, pynp = 2-(2-pyridy1)-1,8-naphthyridine), which exhibits unique irreversible photoisomerization, were assessed in aqueous solution using time-resolved infrared vibrational spectroscopy and quantum chemical calculations. Transient vibrational spectra from 1300 to 1650 cm(-1) were acquired 120 and 2 Ps after photoexcitation with a 400 nm pulse for the distal- and proximal-isomers, respectively. The calculated vibrational spectra assuming the lowest triplet states were in good agreement with the experimentally observed spectra, and the vibrational bands are assigned to normal vibrational modes obtained from calculations. The lifetimes of the excited state were determined to be 9.7 ns and 6.4 ps for the distal- and proximal-isomers, respectively. Based on these results, we determined various characteristic features of these excited states. Despite the large difference in lifetime, both isomers were assigned to the triplet metal-to-ligand charge transfer ((MLCT)-M-3) state and there was almost no difference in the positions of the atoms directly coordinated to the Ru atom. The dissimilarity between the isomers is that the pynp ligands are significantly distorted in the case of the distal-isomer while there is hydrogen bonding between the pynp and OH2 ligands in the proximal-isomer. The strong interaction between the low lying (MLCT)-M-3 state and the ground state presumably causes the very short lifetime and the forbidden photoisomerization of the proximal-isomer, whereas photoisomerization occurs via the thermally populated metal centered ((MC)-M-3) state from the high-lying (MLCT)-M-3 state in the case of the distalisomer. (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jphotochem.2015.06.018

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

distal-[Ru(Cl-tpy)(pynp)Cl](+) (d-2Cl) (Cl-tpy = 4'-chloro-2,2';6',2"-terpyridine, pynp =2-(2-pyridy1)-1,8-naphthyridine), and distal- and proximal-[Ru(Cl-tpy)(pynp)OH2](2+) (d- and p-2H(2)O) complexes are newly synthesized and characterized to compare structures and physicochemical properties with a 2,2';6',2 ''-terpyridine (tpy) ligand derivatives of distal-[Ru(tpy)(pynp)Cl](+) (d-1Cl), distal- and proximal-[Ru(tpy) (PYnP)OH2](2+) (d- and p-1H(2)O). The equilibrium turned out to be involved in the aquation reaction of d-2Cl to d-2H(2)O in contrast to observed irreversible aquation reaction of d-1Cl under the same conditions. The kinetic analysis showed that the aquation reaction of d-2Cl is slightly slower than that of d-1Cl. The stoichiometric photoisomerization of d-2H(2)O to p-2H(2)O occurs by visible light irradiation as it is for d-1H(2)O, and (2.1%) at 520 nm for photoisomerization of d-2H(2)O was higher than that (1.5%) observed for d-1H(2)O. d-2H(2)O undergoes the two-step reaction involving the successive one-proton-coupled oneelectron reactions of the Ru-II-OH2/Ru-III-OH and Ru-III-OH/Ru-IV=O redox couples, whereas p-2H(2)O undergoes the one-step reaction involving the two-proton-coupled two-electron reaction of the RuII-OH2/Ru-IV=O redox couple. These redox potentials of d- and p-2H(2)O are higher than those for d- and p-1H(2)O at pH 7.0 by 10 similar to 50 my due to the electron-withdrawing chloro substitution. The turnover frequency (k(o2) = 6.3 x 10(-3) s(-1)) of d-2H(2)O for water oxidation was higher than that (3.9 x 10(-4) s(-1)) of p-2H(2)O by a factor of 16. k(o2) for d-2H(2)O was also 1.6 times higher than that (3.8 x 10(-3) s(-1)) for d-1H(2)O, whereas k(o2) for p-2H(2)O was 1.2 times lower than that (4.8 x 10(-4) s(-1)) for p-1H(2)O. (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jphotochem.2015.05.029

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

Tetracationic pyrene derivatives (Py4+) and dicationic tris(bipyridine)ruthenium(II) (Ru2+) were hybridized on a synthetic clay (SSA) surface; the hybrid is denoted as Py4+/Ru2+/SSA. The photochemical properties of the Py4+/Ru2+/SSA system, especially the energy transfers from Py4+ to Ru2+, were investigated. Absorption analysis revealed fading of Ru2+; this hypochromic effect suggests that the Ru2+ and Py4+ weakly interacted on the SSA surface. The remarkable quenching of the emission from Py4+ by the coadsorbed Ru2+ was probably stimulated by energy transfer from Py4+ to Ru2+. Emission of Ru2+ was amplified 4-5 times within the Py4+/Ru2+/SSA system; the maximum emission quantum yield of Ru2+ was 30.4 +/- 3.8%. Very interestingly, the three independent photochemical behaviors of By(4+)/Ru2+/SSA, namely fading of Ru2+, stimulation of emission quenching of Py4+, and emission amplification of Ru2+, occurred at almost identical critical amounts of adsorbed Ru2+ (11-13% cation exchange capacity (CEC)). Molecular distribution modeling of the SSA surface suggests that Py4+ and Ru2+ adjoined on the SSA surface when the amount of adsorbed Ru2+ exceeded ca. 11% CEC. On the other hand, the unique photochemical and photophysical properties might arise from the adjoined geometrical arrangement of Py4+ and Ru2+ coadsorbed on the SSA surface. (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jphotochem.2015.05.015

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

Heterogeneous water oxidation catalyses were studied as a synthetic model of oxygen evolving complex (OEC) in photosynthesis using mica adsorbing various manganese species. Distribution of manganese species formed in the oxidative dimerization reaction of [Mn-II(terpy)(2)](2+) (terpy = 2,2':6',2 ''-terpyridine) (1') with various oxidants in water was revealed. 1' was stoichiometrically oxidized to form di-mu-oxo dinuclear manganese complex, [(OH2)(terpy)Mn-III(mu-O)(2)Mn-IV(terpy)(OH2)](3+) (1) by KMnO4 as an oxidant. When Oxone and Ce(IV) oxidants were used, the further oxidation of 1 to [(OH2)(terpy)Mn-IV(mu-O)(2)Mn-IV(terpy)(OH2)](4+) (2) was observed after the oxidative dimerization reaction of 1'. The mica adsorbates with various composition of 1', 1 and 2 were prepared by adding mica suspension to the various oxidant-treated solutions followed by filtration. The heterogeneous water oxidation catalysis by the mica adsorbates was examined using a Ce(IV) oxidant. The observed catalytic activity of the mica adsorbates corresponded to a content of 1 (1(ads)) adsorbed on mica for KMnO4- and Oxone-treated systems, indicating that 1' (1'(ads)) and 2 (2(ads)) adsorbed on mica do not work for the catalysis. The kinetic analysis suggested that lads works for the catalysis through cooperation with adjacent lads or 2(ads), meaning that 2(ads) assists the cooperative catalysis by lads though 2(ads) is not able to work for the catalysis alone. For the Ce(IV)-treated system, O-2 evolution was hardly observed although the sufficient amount of 1(ads) was contained in the mica adsorbates. This was explained by the impeded penetration of Ce(IV) ions (as an oxidant for water oxidation) into mica by Ce3+ cations (generated in oxidative dimerization of 1') co-adsorbed with 1(ads). (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jphotobiol.2015.04.004

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Nanowire of nickel molybdate hydrate, being recognized as an emerging supercapacitor material, was synthesized from the intercrystal self-assembly process (commonly referred to as oriented aggregation or attachment). The detailed lattice image of a NiMoO4 center dot 0.75H(2)O nanowire and the intermediate nanostructure before reaching the interplanar binding were successfully captured by means of high-resolution transmission and scanning electron microscopies. NiMoO4 center dot 0.75H(2)O possessed highly crystalline surface and internal nanostructures.

DOI： 10.1021/acs.inorgchem.5b00625

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

A new series of proximal proximal-[Ru-2(tpy)(2)(L)XY](n+) (p,p-Ru2XY, tpy = 2,2':6',2 ''-terpyridine, L = 5-phenyl-2,8-di(2-pyridyl)-1,9,10-anthyridine, X and Y = other coordination sites) were synthesized using, photoisomerization of a mononuclear complex. The p,p-Ru2XY complexes undergo unusual reversible bridge-exchange reactions to generate p,p-Ru-2(mu-Cl), p,p-Ru-2(mu-OH), and p,p-Ru-2(OH)(OH2) with mu-Cl, mu-OH, as well as hydroxo and aquo ligands at X and Y sites of p,p-Ru2XY, respectively. The geometric and electronic structures of these complexes were characterized based on UV vis and H-1 NMR spectra, X-ray crystallography, and density functional theory (DFT) calculations. H-1 NMR data showed C-2 symmetry of p,p-Ru-2(OH)(OH2) with the distorted L chelate and nonequivalence of two tpy ligands, in contrast to the C-2 symmetry of p,p-Ru-2(mu-Cl) and p,p-Ru-2(mu-OH). However, irrespective of the lower symmetry, p,p-Ru-2(OH)(OH2) is predominantly formed in neutral and weakly basic conditions due to the specially stabilized core structure by multiple hydrogen-bond interactions among aquo, hydroxo, and backbone L ligands. The electrochemical data suggested that p,p-Ru-2(OH)(OH2) (Ru-II-OH:Ru-II-OH2) is oxidized to the Ru-III-OH:Ru-III-OH state at 0.64 V vs saturated calomel electrode (SCE) and further to Ru-IV=O:Ru-IV-OH at 0.79 V by successive 1-proton-coupled 2-electron processes at pH 7.0. The cyclic voltammogram data exhibited that the p,p-Ru-2(OH)(OH2) complex works more efficiently for electrocatalytic water oxidation, compared with a similar mononuclear complex distal-[Ru(tpy)(L)OH2](2+) (d-RuOH2) and p,p-Ru-2(mu-Cl) and p,p-Ru-2(mu-OH), showing that the p,p-Ru-2 core structure with aquo and hydroxo ligands is important for efficient electrocatalytic water oxidation. Bulk electrolysis of the p,p-Ru-2(OH)(OH2) solution corroborated the electrocatalytic cycle involving the Ru-III-OH:Ru-III-OH state species as a resting state. The mechanistic insight into O-O bond formation for O-2 production was provided by the isotope effect on electrocatalytic water oxidation by p,p-Ru-2(OH)(OH2) and d-RuOH2 in H2O and D2O media.

DOI： 10.1021/acs.inorgchem.5b01264

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

The photoisomerization equilibrium between distal- and proximal-[Ru(tpy)(pyqu)OH2](2+) [d- and p-RuH2O, tpy = 2,2;6,2-terpyridine, pyqu = 2-(2-pyridyl)quinoline] is characterized. The kinetic analysis of the pD-dependent photoisomerization reactions (monitored by H-1 NMR) of d-RuH2O and p-RuH2O shows (1) that both hydroxo isomers, distal- and proximal-[Ru(tpy)(pyqu)OH](+), are inert to photoisomerization, and (2) that the back reaction (distal to proximal) is 3.0 times faster than the forward reaction (proximal to distal). Isolation of distal- and proximal-[Ru(tpy)(pyqu)Cl](+) (d- and p-RuCl) as well as d- and p-RuH2O isomers enabled comprehensive studies on geometric structures, ligand exchange and redox reactions, and water oxidation catalysis for these isomers. The observed aquation rate constant (9.2x10(-2)s(-1) at 40 M) of p-RuCl to form p-RuH2O is 1700 times higher than that (5.4x10(-5)s(-1) at 63 M) of d-RuCl at 298 K owing to the steric repulsion between a chloro ligand and the 8-proton of the quinoline moiety. The turnover frequency (TOF = 1.7x10(-3)s(-1)) of p-RuH2O for catalytic water oxidation is 1.7 times greater than that (1.0x10(-3)s(-1)) for d-RuH2O, in contrast to the [Ru(tpy)(pynp)OH2](2+) isomer system, in which the TOF of the distal isomer is higher than that of the proximal one by one order of magnitude. The mechanisms and factors controlling the photoisomerization equilibria and water oxidation catalysis of the d- and p-RuH2O isomers are discussed on the basis of experimental and theoretical investigations.

DOI： 10.1002/ejic.201500642

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The current approaches to electrochemically synthesizing valve metal derived nanochannel films with longitudinal nanospaces aligned at a right angle to planar substrates rely on highly toxic fluoride compounds and require severe reaction conditions. Herein, we report on a fluoride-free, room-temperature, electrochemical synthesis Of a genuine mesoporous niobia thin filth from the parent metal. The electrochemical reaction is driven by only a 1 V bias with respect to a Pt counter electrode in at aqueous solution. The solution contained an inexpensive, less toxic potassium hydroxide, and the reaction produced favorable byproducts, namely, recyclable K8Nb6O19 and H-2.

DOI： 10.1021/ic502580e

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

We report the first accessible channel-like open pore architecture of ordered 2D hexagonal mesoporous IrO2 films and its utilization as an efficient anode for electrocatalytic water oxidation. A well-ordered mesostructure of circa 7nm pores were obtained by a facile one-pot soft-templating strategy, employing a [Ir(OH)(6)](2-) precursor stabilized by a triblock copolymer PluronicF127 as a pore-directing template. A mesoporous IrO2 film calcined at 400 degrees C (approximate to 70nm thick) affords a high surface area of 512m(2)cm(-3) and 2times higher O-2 evolution during the electrocatalytic water oxidation relative to an untemplated IrO2 coating film.

DOI： 10.1002/cssc.201402911

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Tetra-cationic pyrene derivative (Py4+) and tris(bipyridine)ruthenium(II) (Ru2+) were hybridized onto the surface of a synthesized clay. We observed the remarkable stimulation of excited Py4+ emission quenching on the clay surface, with a very large apparent quenching rate constant (k(q) = 7.4 +/- 0.7 x10 (15) L mol(-1) s(-1)).

DOI： 10.1021/la504597t

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Tungsten trioxide (WO3) films with nanoporous morphology were prepared by a facile and simple method utilizing commercially available WO3 nanopowder with polyethylene glycol to guide porosity of a nanostructure, and the resulted photoanode was working efficiently for visible-light-driven water oxidation. The SEM observation and XRD measurement revealed formation of interparticulate nanopores between the well-connected WO3 crystaline particles of dimension ca. 100-200 nm. The nanoporous WO3 electrode generated a significant photoanodic current density of 1.8 mA cm(-2) due to water oxidation at 1.0 V versus Ag/AgCl on visible light irradiation (lambda&gt;390 nm, 100 mW cm(-2)). The onset potential of the WO3 electrode was 0.67 V versus a reversible hydrogen electrode (RHE), being lower by 0.56 V than the theoretical potential for water oxidation (1.23 V versus RHE). The incident photon to current conversion efficiency (IPCE) reached 45% at 400 nm of light wavelength and 1.04 V versus Ag/AgCl of an applied potential. The photoanodic current and photostability of the WO3 electrode were improved by addition of Co2+ ions in the electrolyte solution during photoelectrocatalysis. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijhydene.2014.06.062

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

The influencing factors on heterogeneous water oxidation catalysis (WOC) were investigated in a synthetic photosystem II model developed by adsorbing [(OH2)(terpy)Mn-III(mu-O)(2)Mn-IV(terpy)(OH2)](3+) (terpy = 2,2':6',2aEuro(3)-terpyridine) (1) as an oxygen evolving center onto mica. For chemical WOC using a Ce4+ oxidant, the catalytic activity of 1 on mica increased by a factor of 2.3 or 1.4 by co-adsorption (0.015 mmol g(-1)) of redox-inactive trications of Al3+ or Ce3+ with 1 (0.15 mmol g(-1)), respectively, whereas it decreased by co-adsorption (0.25 mmol g(-1)) of excess Al3+ or Ce3+. The cooperative catalysis by two equivalents of the adsorbed 1 for water oxidation could be facilitated by enrichment of 1 by trications at their low co-adsorption conditions. The decreased catalytic activity at high trications co-adsorption conditions could be explained by impeded penetration of Ce4+ oxidant ions into a mica interlayer. For photochemical WOC containing a [Ru(bpy)(3)](2+) (bpy = 2,2'-bipyridine) photoexcitation center in mica, the drying treatment at 65 A degrees C under the vacuum after 1 adsorption was required in adsorbate preparation, possibly to maintain favorable arrangement of 1 and [Ru(bpy)(3)](2+) in a mica interlayer. The drying treatment at 65 A degrees C under the vacuum after [Ru(bpy)(3)](2+) adsorption inactivated the photochemical WOC. The proton-coupled electron transport from interior [Ru(bpy)(3)](2+) centers to ones near the surface in mica is considered to be suppressed by the drying treatment, which could be responsible for the inactivated photochemical WOC.

DOI： 10.1007/s11164-014-1826-z

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

Mesoporous tungsten trioxide (WO3) was prepared from tungstic acid (H2WO4) as a tungsten precursor with dodecylamine (DDA) as a template to guide porosity of the nanostructure by a solvothermal technique. The WO3 sample (denoted as WO3-DDA) prepared with DDA was moulded on an electrode to yield efficient performance for visible-light-driven photoelectrochemical (PEC) water oxidation. Powder X-ray diffraction (XRD) data of the WO3-DDA sample calcined at 400 degrees C indicate a crystalline framework of the mesoporous structure with disordered arrangement of pores. N-2 physisorption studies show a Brunauer-Emmett-Teller (BET) surface area up to 57 m(2) g(-1) together with type IV isotherms and uniform distribution of a nanoscale pore size in the mesopore region. Scanning electron microscopy (SEM) images exhibit well-connected tiny spherical WO3 particles with a diameter of ca. 5 to 20 nm composing the mesoporous network. The WO3-DDA electrode generated photoanodic current density of 1.1 mA cm(-2) at 1.0 V versus Ag/AgCl under visible light irradiation, which is about three times higher than that of the untemplated WO3. O-2 (1.49 mu mol; Faraday efficiency, 65.2%) was evolved during the 1-h photoelectrolysis for the WO3-DDA electrode under the conditions employed. The mesoporous electrode turned out to work more efficiently for visible-light-driven water oxidation relative to the untemplated WO3 electrode.

DOI： 10.1186/1556-276X-9-542

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

We compared the survival rates and late effects for two groups of cervical cancer patients treated with almost the same external radiotherapy but different remote afterloading systems (RALS) for high-dose-rate intracavitary radiation therapy regimens. A total of 218 patients with carcinoma of the uterine cervix were treated. For 98 patients, intracavitary brachytherapy was delivered with 6-7.5 Gy/fraction to Point A (Group A), and for 120, 5 Gy/fraction with a modified source step size (Group B). The 3-year cause-specific survival rates by stage and treatment schedule were Group A: 91% and Group B: 96% in Stage I, 89% and 92% in Stage II, 64% and 75% in Stage III, 44% and 69% in Stage IV. The survival curves did not reveal any statistically significant differences at any stage. The 3-year cumulative local failure rates were 14% in Group A and 7% in Group B (P = 0.1202), while the actuarial rates of developing rectal complication (Grade 2 or more) at 3 years were 25% in Group A and 4% in Group B (P &lt; 0.0001). This retrospective analysis suggests that a low dose per fraction with modified source step size is advantageous because of yielding almost the same local control but with fewer rectal complications.

DOI： 10.1093/jrr/rrt226

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

Artificial photosynthesis is one of the promising clean-energy-providing systems of the future. Development of an efficient catalyst for water oxidation to evolve O-2 is indispensable for the construction of artificial photosynthetic devices. The photosynthetic oxygen evolving complex (OEC) composed of a tetranuclear manganese cluster serves as an excellent example of an efficient catalyst for water oxidation. Recently, significant progress has been reported in the development of manganese complexes as OEC models. The molecular aspects and activities of these manganese complexes toward water oxidation catalysis were reviewed in terms of homogeneous and heterogeneous catalysis systems. These could provide hints to design an efficient catalyst, as well as a key model reaction to understand the O-2 evolution mechanism in photosynthesis.

DOI： 10.1002/ejic.201300683

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

A polychromium-oxo-deposited TiO2 electrode was fabricated as an earth-abundant photoanode for visible-light-driven water oxidation by a simple electrochemical technique. The photoelectrocatalytic water oxidation could occur based on a specific interfacial charge transfer (IFCT) from a Cr-III to the TiO2 conduction band.

DOI： 10.1039/c3cc47764a

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

DOI： 10.1002/anie.201306004

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

We report a template-free facile technique that allows for the first ever synthesis of a monoclinic Ag2Mo2O7 nanowire (m-Ag2Mo2O7-NW), using a commercially available MoO3 particle. The nanowire possessed high crystallinity and structural homogeneity and strongly suggested that the nanowire was grown through an oriented aggregation mechanism in contrast to the case of a typical solution-phase method. The corresponding bulky counterpart showed no photoresponse; however, a complete structural transformation toward a nanowire triggered activity for O-2 evolution in the presence of Ag+ as an electron acceptor under visible-light irradiation.

DOI： 10.1021/ic401236b

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A photosynthetic photosystem II (PS II) model was developed by adsorbing [(OH2)(terpy)MnIII(μ-O)2Mn IV(terpy)(OH2)]3+ (1, terpy = 2,2′:6′,2″-terpyridine) as an oxygen evolving center and Ru(bpy)32+ (bpy = 2,2′-bipyridine) as a photoexcitation center onto mica. The mica adsorbates were prepared by three different methods
Adsorbate A was prepared by adsorption of 1 followed by Ru(bpy)32+ on mica, and Adsorbates B and C were prepared by the opposite adsorption order and co-adsorption of 1 and Ru(bpy) 32+, respectively. The UV-visible diffuse reflectance (DR) spectroscopic data and emission decay measurements of the photoexcited Ru(bpy)32+ suggested the different arrangements of 1 and Ru(bpy)32+ among the three adsorbates in a mica interlayer. For Adsorbate A, Ru(bpy)32+ could be adsorbed near the mica surface, being shallowly intercalated relative to 1. For Adsorbate B, 1 is adsorbed near the mica surface, Ru(bpy)32+ being deeply intercalated relative to 1. For Adsorbate C, either 1 or Ru(bpy) 32+ could be randomly intercalated relative to the other adsorbates. In photochemical water oxidation experiments, a significant amount of O2 was evolved when visible light was used to irradiate an aqueous suspension of Adsorbate A containing a S2O82- electron acceptor in a liquid phase, whereas O2 was not evolved under the same conditions when using Adsorbates B and C. 1 is considered to work for photochemical water oxidation in Adsorbate A due to an efficient electron transport from deeply intercalated 1 to S2O82- ions in a liquid phase via Ru(bpy)32+ photoexcitation near the mica adsorbate surface. © 2013 The Royal Society of Chemistry.

DOI： 10.1039/c3cy00010a

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A ligation of Ru(tpy)Cl3 (tpy = 2,2′:6′,2″- terpyridine) with 2-(2-pyridyl)-1,8-naphthyridine) (pynp) in the presence of LiCl gave distal-[Ru(tpy)(pynp)Cl]+ (d-1Cl) selectively, whereas the ligation gave proximal-[Ru(tpy)(pynp)OH2]2+ (p-1H 2O) selectively in the absence of halide ions. (The proximal/distal isomers were defined by the structural configuration between the 1,8-naphthyridine moiety and the aquo or chloro ligand.) An aquation reaction of d-1Cl quantitatively afforded distal-[Ru(tpy)(pynp)OH2]2+ (d-1H2O) in water, and d-1H2O is quantitatively photoisomerized to p-1H2O. The mechanism of the photoisomerization was investigated by transient absorption spectroscopy and quantum chemical calculations. The temperature dependence of the transient absorption spectral change suggests existence of the thermally activated process from the 3MLCT state with the activation energy (ΔE = 49 kJ mol -1), which is close to that (41.7 kJ mol-1) of the overall photoisomerization reaction. However, quantum chemical calculations suggest another activation process involving the conformational change of the pentacoordinated distal structure to the proximal structure. Quantum chemical calculations provide redox potentials and pKa values for proton-coupled electron transfer reactions from RuII-OH2 to RuIV=O in good agreement with experiments and provide an explanation for mechanistic differences between d-1H2O and p-1H 2O with respect to water oxidation. The calculations show that water nucleophilic attack (WNA) on d-[RuV-O]3+ (the ruthenyl oxo species derived from d-1H2O, calculated ΔG ⧧ of 87.9 kJ/mol) is favored over p-[Ru V-O]3+ (calculated ΔG⧧ of 104.6 kJ/mol) for O-O bond formation. Examination of the lowest unoccupied molecular orbitals in d-and p-[RuV-O]3+ indicates that more orbital amplitude is concentrated on the [Ru-O] unit in the case of d-[RuV-O]3+ than in the case of p-[RuV-O] 3+, where some of the amplitude is instead delocalized over the pynp ligand, making this isomer less electrophilic. © 2013 American Chemical Society.

DOI： 10.1021/ic400054k

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A new MnIII (μ-O)2MnVI dimer, [(OH 2)(Py-terpy)Mn(μ-O)2Mn(Py-terpy)(OH2)] 3+ (Py-terpy = 4′-(4-pyridyl)-2,2′:6′,2″- terpyridine) (1Py) with electron-withdrawing pyridyl (Py) groups was synthesized and characterized by UV-Vis and IR spectroscopic, X-ray crystallographic, magnetometric, and electrochemical techniques. 1Py is stable in an aqueous solution at room temperature, in contrast to the unstable Cl and Br derivatives with R-terpy (R = Cl or Br of electron-withdrawing groups). The maximum concentrations of 1Py adsorbed on saponite suggests that 1Py is adsorbed on saponite or mica as a pentavalence cation, like [1Py2H]5+ with protonation of Py groups on Py-terpy ligands. Water oxidation catalyses by 1Py were examined in homogenous solution and heterogeneous saponite or mica adsorbate systems. O2 was evolved in a reaction of 1Py with a Ce(IV) oxidant in an aqueous solution. However, the maximum turnover number (TN) of 1Py for O2 evolution was 0.63 for 4 days, showing that 1Py does not work as a catalyst for water oxidation in solution. The reactions of the 1Py/saponite or mica adsorbate with a CeIV oxidant in water catalytically produced the significant amount of O2. The maximum TNs of 1Py on saponite and mica for O2 evolution are 5.6 and 16 for 4 days, respectively. The kinetic analysis of O2 evolution suggested that the unimolecular decomposition reaction of 1Py involving O2 evolution competes with the cooperative catalysis by two equivalents of 1Py on saponite or mica. The k2 values of 1Py adsorbates were lower than those of 1 adsorbates for saponite and mica systems, in contradiction to the magnitude relationship predicted from the E1/2 values of 1Py and 1 based on our previous work (Yamazaki et al., 2012 [29]). The lower k2 values could be explained most possibly by electrostatic repulsion between a pentavalent [1Py2H]5+ cation on saponite and mica, compared with a trivalent 1 cation.

DOI： 10.1016/j.poly.2012.08.051

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Language：Japanese   Publisher：The Biophysical Society of Japan General Incorporated Association  

DOI： 10.2142/biophys.53.S83_1

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

[(OH2)(R-terpy)Mn(mu-O)(2)Mn(R-terpy)-(OH2)](3+) (R-terpy = 4'-substituted 2,2':62 ''-terpyridine, R = butoxy (BuO), propoxy (PrO), ethoxy (Et0), methoxy (MeO), methyl (Me), methylthio (MeS), chloro (Cl)) have been synthesized as a functional oxygen-evolving complex (OEC) model and characterized by UV-vis and IR spectroscopic, X-ray crystallographic, magnetometric, and electrochemical techniques. The UV-vis spectra of derivatives in water were hardly influenced by the 4'-substituent variation. X-ray crystallographic data showed that Mn centers in the Mn-III(mu-O)(2)Mn-IV cores for derivatives with R = H, MeS, Me, EtO, and BuO are crystallographically indistinguishable, whereas the derivatives with R = MeO and PrO gave the significantly distinguishable Mn centers in the cores. The indistinguishable Mn centers could be caused by rapid electron exchange between the Mn centers to result in the delocalized Mn(mu-O)(2)Mn core. The exchange integral values (J = -196 to -178 cm(-1)) for delocalized cores were lower than that (J= -163 to -161 cm(-1)) for localized cores, though the Mn center dot center dot center dot Mn distances are nearly the same (2.707-2.750 angstrom). The half wave potential (E-1/2) of a Mn-III-Mn-IV/Mn-IV-Mn-IV pair of the derivatives decreased with an increase of the electron-donating ability of the substituted groups for the delocalized core, but it deviated from the correlation for the localized cores. The catalytic activities of the derivatives on mica for heterogeneous water oxidation were remarkably changed by the substituted groups. The second order rate constant (k(2)/mol(-1) s(-1)) for O-2 evolution was indicated to be correlated to E-1/2 of a Mn-III-Mn-IV-Mn-IV pair; k(2) increased by a factor of 29 as E-1/2 increased by 28 mV.

DOI： 10.1021/ic201797h

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

The aim of this study was to investigate the role of the combined use of customized molds and a high dose rate (HDR) remote afterloading brachytherapy apparatus with a Ir-192 microsource in the treatment of superficial oral carcinomas after chemoradiotherapy.
Nine patients with oral squamous cell carcinoma who were treated using this combined technique were analyzed retrospectively. The primary sites of the tumors were the mouth floor, gingiva, and soft palate. For each patient, a customized mold was fabricated in which 2-3 afterloading catheters were placed for the Ir-192 source. Three to eight fractions of 3 Gy, 5 mm below the mold surface, were given following external radiotherapy of 24-50 Gy/2 Gy combined with chemotherapy (peplomycin or taxotere). The total dose of HDR brachytherapy ranged from 9 to 24 Gy.
The 2-year local control probability was 100% and the 2-year cause-specific survival rate was 100%. No serious complications (i.e., ulcer or bone exposure) have been observed thus far during the follow-up period of 29-120 months.
HDR brachytherapy using the mold technique after chemoradiotherapy is a safe and excellent method for selected early and superficial oral cavity cancers.

DOI： 10.1007/s11604-011-0005-z

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Although various reactions involved in photoexcited states of polypyridyl ruthenium(II) complexes have been extensively studied, photoisomerization of the complexes is very rare. We report the first illustration of stoichiometric photoisomerization of trans-[Ru(tpy)(pynp)OH(2)](2+) (1a) [tpy = 2,2&apos;:6&apos;,2 &apos;&apos;-terpyridine; pynp = 2-(2-pyridyl)-1, 8-naphthyridine] to cis-[Ru(tpy)(pynp)OH(2)](2+) (1a&apos;) and the isolation of 1a and 1a&apos; for X-ray crystallographic analysis. Polypyridyl ruthenium(II) aquo complexes are attracting much attention related to proton-coupled electron transfer and water oxidation catalysis. We demonstrate that the photoisomerization significantly controls the redox reactions and water oxidation catalyses involving the ruthenium(II) aquo complexes 1a and 1a&apos;.

DOI： 10.1021/ja2024228

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

The catalytic activity of [Ru(tpy)(bpy)OH2](2+) (tpy = 2,2': 6', 2 ''-terpyridine and bpy = 2,2'-bipyridine) increased by a 4'-substituted ethoxy group on the tpy ligand by more than one order of magnitude to give 1.1 x 10(-1) s(-1) of catalyst turnover frequency, which is comparable with the hitherto-reported champion data.

DOI： 10.1039/c0dt01826k

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Language：English   Publisher：The Biophysical Society of Japan General Incorporated Association  

DOI： 10.2142/biophys.51.S10_5

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

Citrate-stabilized Pt colloid nanoparticles were self-assembled on an indium tin oxide (ITO) electrode when it was immersed in a colloid solution at pH 4.0. The preparation technique of an electrode catalyst by the self-assembly of Pt colloid particles takes advantage of the very strong attachment of the colloid particles on the electrode surface due to the chemical interactions, as well as the effective use of Pt without waste, in principle. The Pt colloid-assembled (PCA) electrode performed both stably and effectively during electrocatalysis for proton reduction compared with a conventional Pt thermal-deposited (PTD) electrode.

DOI： 10.1039/c0gc00476f

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

The construction of an artificial photosynthetic device requires detailed understanding of the catalytic aspects of photo- or photoelectro-driven water oxidation. This has been attracting much interest as one of the promising clean energy-providing systems for the future. This review mainly covers progress on electrocatalytic and photocatalytic systems for water oxidation in the last decade. It includes conventional iridium oxide colloid catalysts and the new electrodeposited cobalt-phosphate catalyst films for water oxidation. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.ccr.2010.02.008

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

Visible-light-derived O-2 production was yielded by conjugating water oxidation catalysis by [(OH2)(terpy)Mn(mu-O)(2)Mn-(terpy)(OH2)](3+) as an oxygen evolving center model and photo-sensitization of [Ru(bpy)(3)](2+) as a photoexcitation center model at an interlayer of mica.

DOI： 10.1039/c0cc03114c

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

A plate-type alumina support was synthesized through a novel anodization technology followed by a hot water treatment, which resulted in the drastically enlargement of support BET surface area from 16.5 to 204.6 g/m(2), and such BET value is even comparable to some commercial alumina supports. A high thermal stability of this kind of porous anodic alumina support was shown because as much as 63% of surface area remained after the support subjected to 700 degrees C air calcination for 50 h. Innovatively, an electrical heating pattern was allowed over this plate support due to the existence of Fe-Cr-Ni alloy interlayer among the support. Our work showed that the utilization of electrical heating pattern would shorten the reformer start-up time from 1 to 2 h to just a few minutes. With the porous anodic alumina support, a 17.9-wt% Ni catalyst with nickel aluminate layer was synthesized and its reforming reactivity was investigated during stationary and DSS SRM at 700 degrees C, under usual and electrical heating pattern. It showed excellent SRM reactivity and no deactivation was evidenced during 500 h stationary test and 100 times start-stop cycles DSS SRM test. Nevertheless, for the industrialization, some efforts should be made to alleviate the sintering of anodic supports, because after subjected to a hydrothermal treatment at 700 degrees C for 50 h, only 36% of surface area was kept. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijhydene.2008.10.057

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

A single-wall carbon nanotube functionalized by carboxylic groups (SWNT-CA) was found to be adsorbed on an indium tin oxide (ITO) electrode by chemical interaction between carboxylic groups and the ITO surface. The adsorption experiments indicated that the narrow pH conditions (around pH 3.0) exist for its adsorption which is restricted by preparation of stable fluid dispersion (favorable at higher pH) and by the chemical interaction (favorable at lower pH). Atomic force microscopic (AFM) measurements suggest that fragmented SWNT-CA are adsorbed, primarily lying on the surface. Electrochemical impedance analysis indicated that an electrochemical double layer capacitance of the SWNT-CA/ITO electrode is considerably higher than that for the ITO electrode. suggesting that the interfacial area between the electrode Surface and the electrolyte solution is enlarged by the SWNT-CA layer. Pt particles were deposited as a catalyst on the bare ITO and SWNT-CA-coated ITO (SWNT-CA/ITO) electrodes to give respective Pt-modified electrodes (denoted as a Pt/ITO electrode and a Pt/SWNT-CA/ITO electrode, respectively). The cathodic current for the Pt/SWNT-CA/ITO electrode was 1.7 times higher than that for the Pt/ITO electrode at 0.0 V, showing that the Pt/SWNT-CA/ITO electrode works more efficiently for O-2 reduction at 0.0 V due to the SWNT-CA layer. The enhancement by the SWNT-CA layer is also effective for electrocatalytic proton reduction. It could be ascribable to the enlarged interfacial area between the electrode Surface and the electrolyte solution.

DOI： 10.1002/elan.200804412

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SOC CHEMICAL ENG JAPAN  

An anodic alumina supported 17.9 wt% Ni catalyst shows an excellent catalytic performance during steam reforming of methane at 700 C under W/F = 6.33 x 10(-3) g.cat.h/L, even when compared with some commercial Ni and Ru reforming catalysts. This is considered to be the result of the existence of an interfacial NiAl(2)O(4) layer, which could anchor the top metallic nickel particles to prevent them from reacting with the alumina support and sintering, thereby, effectively suppressing carbon deposition. Nevertheless, for the industrialization of anodic nickel catalysts, some effort should be made to alleviate the deterioration of anodic supports, because when subjected to a higher W/F as 1.27 x 10(-3) g.cat.h/L, the catalyst shows irreversible deactivation, and little improvement is seen by increasing nickel spinel content and metal loading or modifying the impregnation solution pH.

DOI： 10.1252/jcej.08we192

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

It was earlier reported that [(OH2)(terpy)Mn(mu-O)(2)Mn(terpy)(OH2)](3+) (terpy = 2,2&apos;:6&apos;,2 &apos;&apos;-terpyridine) (1) adsorbed on layer compounds catalyzes water oxidation to O-2 (J. Am. Chem. Soc., 2004, 126, 8084). The derivative with 4&apos;-chloro-2,2&apos;:6&apos;,2 &apos;&apos;-terpyridine (Clterpy), [(OH2)(Clterpy) Mn(m-O)(2)Mn(Clterpy)(OH2)](NO3)(3) (2(NO3)(3)) was synthesized and characterized by UV-visible absorption spectroscopic and magnetic susceptibility measurements. 2 is instable in aqueous solution at room temperature, but the stability of 2 in solution significantly increased at 5 degrees C. The reaction of a 2-mica adsorbate with Ce-IV in water produced a significant amount of O-2, although the reaction of 2 with CeIV in a homogenous solution did not. However, the maximum turnover number (TN = 0.52) of 2 on the mica adsorbate was less than unity, indicating the non-catalytic O-2 evolution by 2 on mica in contrast to the cooperative catalysis by 1 on mica with TN = 15. The kinetic analysis showed that O-2 evolution follows first order kinetics with respect to 2 adsorbed on mica, with the first-order rate constant given to be 6.8 X 10(-5) s(-1). The first order kinetics can be explained by O-2 evolution involved in the unimolecular decomposition of 2 adsorbed on mica, which might be ascribed to the destabilized higher oxidation state of 2 due to the electron-withdrawing chloro-substitution.

DOI： 10.1039/b814885f

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Language：English   Publisher：ROYAL SOC CHEMISTRY  

Artificial photosynthesis is anticipated as one of the promising clean energy- providing systems for the future. The development of an efficient catalyst for water oxidation to evolve O(2) is a key task to yield a breakthrough for construction of artificial photosynthetic devices. Recently, significant progress has been reported in the development of the molecular catalysts for water oxidation based on manganese, ruthenium and iridium. The molecular aspects of the catalysts reported in the last decade were reviewed to provide hints to design an efficient catalyst, as well as to gain clues to reveal the mechanism of O(2) evolution at photosynthetic oxygen evolving complex in nature.

DOI： 10.1039/b811098k

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

A 17.9 wt.% Ni/Al(2)O(3)/alloy catalyst with porous anodic alumina Support was Subjected to steam reforming of methane after 700 degrees C steam purging and no reactivity was shown because of surface oxidation of sintered Ni particles. When 0.05 wt.% Ru doped on this catalyst, it exhibited self-activation and self-regenerative activity, resulted from the hydrogen spillover over Ru and/or Ru-Ni alloy. Moreover, a 97% CH(4) conversion was kept for 20 h over the Catalyst Under electrical heating pattern. (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.catcom.2008.09.029

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

A [Ru(bpy)(3)](2+) (bpy = 2,2'-bipyridine)/WO3 hybrid (denoted as Ru-WO3) film was prepared as a base layer on an indium tin oxide electrode by electrodeposition from a colloidal solution containing peroxotungstic acid, [Ru(bpy)(3)](2+) and poly(sodium 4-styrenesulfonate). A ruthenium purple (RP, Fe-4(III)[Ru-II(CN)(6)](3), denoted as Fe-III-Ru-II) layer was electrodeposited on a neat WO3 film or a Ru-WO3 film from an aqueous RP colloid solution to yield a WO3/RP bilayer film or a Ru-WO3/RP bilayer film, respectively. The spectrocyclic voltammetry measurement reveals that Fe-II-Ru-II is oxidized to Fe-II-Ru-II by a geared reaction of [Ru(bpy)(3)](2+/3+) and Fe-III-Ru-II is reduced by a geared reaction of HxWO3/WO3 in the Ru-WO3/RP film. These geared reactions produced electrochromic hysteresis of the RP layer. However, the absorbance change in the hysteresis was smaller than that for the Ru-WO3/Prussian blue bilayer film reported previously, resulting from the lower electroactivities of any redox component for the Ru-WO3/RP film. The lower electroactivities could be explained by the specific interface between the Ru-WO3 and RP layers. It might contribute to either an increase of the interfacial resistance between the Ru-WO3 and RP layers, or formation of the physically precise interface between the layers to make it difficult for counter ions to be transported in the interfacial liquid phase involved in the redox reactions in the film. The specific interface at the Ru-WO3 and RP layers could be formed possibly by the electrostatic interaction between [Ru(bPY)(3)](2+) and terminal [Ru(CN)(6)](4-) moieties of RP. It could be suggested by the decreased redox potential of [Ru(bPY)(3)](2), in the Ru-WO3 layer from 1.03 to 0.61 V by formation of the RP layer. (C) 2008 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.electacta.2008.04.069

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

An IrO(2) colloid stabilized by citrate ions was self-assembled on an indium tin oxide (ITO) electrode when it was immersed in the colloid solution at pH 3.5. The IrO2 colloid on the ITO surface was characterized using electrochemical, inductively coupled plasma mass spectroscopic, X-ray diffraction spectroscopic, scanning electron microscopic, and atomic force microscopic techniques. The self-assembly was promoted steeply at pH 3.5 to 4.1, although it hardly occurred at pH 5.3 to 9.7. It is considered to be caused by chemical interaction between carboxylic groups on the citrate stabilizer and hydroxyl groups of the ITO surface. The adsorption isotherm of the IrO(2) colloid onto the ITO surface was analyzed by a Langmuir adsorption isotherm to provide the maximum coverage and an adsorption equilibrium constant Gamma(max) = 1.1 x 10(-8) mol cm(-2) and K(ads) = 1.8 x 10(4) M(-1) at 25 degrees C, respectively. The K(ads) value increased from 6.7 x 10(3) to 1.8 x 10(4) M(-1) with a temperature increase from 5 to 25 degrees C. The temperature dependence of K(ads) gave Delta H degrees = 36.5 kJ mol(-1), Delta G degrees = -24.4 kJ mol(-1), and Delta S degrees = 204 J mol(-1) K(-1) at 25 degrees C. The positive Delta H degrees and Delta S degrees values are explained by the rearrangement of solvating water molecules and counter cations surrounding the IrO2 colloid that is involved in its assembly on the ITO surface. In electrocatalytic water oxidation, the maximum turnover frequency of the IrO(2) catalyst was 23 600 h(-1) under potential static conditions at 1.3 V versus Ag/AgCl.

DOI： 10.1021/jp7098416

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ACADEMIC PRESS INC ELSEVIER SCIENCE  

A tungsten trioxide (WO3) film was prepared by calcination from a precursor paste including suspended ammonium tungstate and polyethylene glycol (PEG). The ammonium tungstate suspension was yielded by an acid-base reaction of tungstic acid and an ammonium solution followed by deposition with ethanol addition. Thermogravimetric (TG) analysis showed that the TG profile of PEG is significantly influenced by deposited ammonium tungstate, suggesting that PEG is interacting strongly with deposited ammonium tungstate in the suspension paste. X-ray diffraction (XRD) data indicated that the WO3 film is crystallized by sintering over 400 degrees C. The scanning electron microscopic (SEM) measurement showed that the film is composed of the nano-structured WO3 platelets. The semiconductor properties of the film were examined by Mott-Schottky analysis to give flat band potential E-FB = 0.30 V vs. saturated calomel reference electrode (SCE) and donor carrier density N-D = 2.5 x 10(22) cm(-3), latter of which is higher than previous WO3 films by two orders of magnitude. The higher ND was explained by the large interfacial heterojunction area caused by the nano-platelet structure, which apparently increases capacitance per a unit electrode area. The WO3 film sintered at 550 degrees C produced 3.7 mAcm(-2) of a photoanodic current at 1.2 V vs. SCE under illumination with a 500 W xenon lamp due to catalytic water oxidation. This photocurrent was 4.5-12.8 times higher than those for the other control WO3 films prepared by similar but different procedures. The high catalytic activity could be explained by the nano-platelet structure. The photocurrent was generated on illumination of UV and visible light below 470 nm, and the maximum incident photon-to-current conversion efficiency (IPCE) was 47% at 320 nm at 1.2 V. Technically important procedures for preparation of nano-structured platelets were discussed. (c) 2007 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.jssc.2007.11.018

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

A nanocomposite film of tungsten trioxide (WO3) and [Ru(bpy)(3)](2+) (bpy = 2,2'-bipyridine) (denoted as Ru-WO3) was prepared from an aqueous colloidal triad solution containing peroxotungstic acid, [Ru(bpy)(3)](2+), and poly(sodium 4-styrenesulfonate) by an electrodeposition technique. The electrochemical features of the Ru-WO3 film were investigated using cyclic voltammetry (CV) and potential-step chronoamperospectrometry (PSCAS) techniques, compared with those in a [Ru(bpy)(3)](2+)/Nafion (Ru-Nf) film. PSCAS data spectrophotometrically showed that Ru-II is completely oxidized for 0.3 s in the Ru-WO3 film, in contrast to the corresponding reaction completed for 30 s in the Ru-Nf film. The apparent diffusion coefficient (D-app = (0.1-1.1) x 10(-7) cm(2) s(-1)) for charge transport (CT) by a Ru-II/Ru-III redox in the Ru-WO3 film was higher than that (2.4 x 10(-10) cm(2) s(-1)) in the Ru-Nf film by 2 or 3 orders of magnitude. Activation energy (E-a) for CT (14.1 kJ mol(-1)) for the Ru-WO3 film was 3.5 times lower than that (E-a = 49.8 kJ mol(-1)) for the Ru-Nf film. The lower E-a could be responsible for the faster CT in the Ru-WO3 film than the Ru-Nf film. D-app in the Ru-WO3 film increased linearly with an increase of the final applied potential (E-f) for PSCAS from 1.2 to 1.5 V vs SCE and saturated above E-f = 1.5 V. The mechanism for CT in the Ru-WO3 film is proposed, in which electrons are injected from [Ru(bpy)(3)](2+) into the conduction band (CB) of WO3 and go through there to a collector electrode.

DOI： 10.1021/jp073020x

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Adsorption of [(OH2)(terpy)Mn(mu-O)(2)Mn(terpy)(OH2)](3+) (terpy=2,2':6',2 ''-terpyridine) (1) onto montmorillonite K10 (MK10) yielded catalytic dioxygen (O-2) evolution from water using a Ce-IV oxidant. The Mn K-edge X-ray absorption near edge structure (XANES) of the 1/MK10 hybrid suggested that the oxidation state of the di-mu-oxo Mn-2 core could be Mn-III-Mn-IV. However the pre-edge peak in the XANES spectrum of 1 adsorbed on MK10 is different from the neat 1 powder. The kinetic analysis of O-2 evolution showed that the catalysis requires cooperation of two equivalents of 1 adsorbed on MK10. The reaction of the [(bpy)(2)Mn(mu-O)(2)Mn(bpy)(2)](3+) (bpy=2,2'-bipyridine) (2)/MK10 hybrid with a Ce-IV oxidant evolved O-2. However, the turnover number value was less than unity for 2/MK10, showing that 2 adsorbed on MK10 does not work as a catalyst. The terminal water ligands could be an important for the catalysis by adsorbed 1. The mechanism of O-2 production by photosynthetic oxygen evolving complex is discussed based on catalytic O-2 evolution by 1 adsorbed on MK10. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.bbabio.2006.11.005

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

A hybrid film of WO3/tris(2,2'-bipyridine)ruthenium(II) ([Ru(bpy)(3])(2+)) /poly(sodium 4-styrenesulfonote) (PSS) (denoted as a WRP hybrid film) was prepared as a base layer on an indium tin oxide electrode substrate by cathodic electrodeposition from a colloidal ternary solution containing peroxotungstic acid, [Ru(bpy)(3)](2+), and PSS. Prussian blue, Fe-4(III)[Fe-II(CN)(6)](3) (Fe-II-Fe-III) was cathodically electrodeposited on the WRP hybrid film from a Berlin brown (Fe-II-Fe-III) colloidal solution to give a WRP/Fe-II-Fe-III biloyer film. Spectrocyclic voltammetry measurement of the WRP/ Fe-II-Fe-III bilayer film reveals that Prussian white (Fe-II-Fe-III) is oxidized to Fe-II-Fe-III by electrogenerated Ru-III, and Fe-II-Fe-III is re-reduced to Fe-II-Fe-III by electrogenerated HxWO3. Visible-light irradiation of the WRP hybrid film generates a small photocurrent (approximate to 8 nA cm(-2)) at 0.4 V of an applied potential, whereas irradiation of the WRP/Fe-II-Fe-III bilayer film (Fe-II-Fe-III is electrochemically reduced to the Fe-II-Fe-III state) significantly generates a steady photoonodic current of 2.0-1.1 mu A cm(-2) under the some conditions, thus demonstrating that the photoanodic current is produced by the layered Fe-II-Fe-III film. The photoaction spectrum of the bilayer film reveals that the photoanodic current is based on the photoexcitation of [Ru(bpy)(3)](2+). The photogeneration of Fe-II-Fe-III from Fe-II-Fe-III is shown by the absorption spectral change of the bilayer film on irradiation. These results corroborate the notion that Fe-II-Fe-III is oxidized by photogenerated Ru-III to generate Fe-II-Fe-III. However, the rote of photogenerotion of Fe-II-Fe-III is slow, which could be ascribed to the fast back electron transfer (ET) from WO3 to Ru-III, comparable with the forward ET from Fe-II-Fe-III to Ru-III. The fast back ET could be a crucial problem for the [Ru(bpy)(3)](2+)-sensitized reaction in the hybrid film.

DOI： 10.1002/cphc.200700192

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Language：English   Publisher：AMER CHEMICAL SOC  

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Language：English   Publishing type：Research paper (international conference proceedings)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Hybridization of [(OH2)(terpy)Mn(mu-O)(2)Mn(terpy)(OH2)](3+)(terpy) 2,2' :6',2''- terpyridine) (1) and mica clay yielded catalytic dioxygen (O-2) evolution from water using a Ce-IV oxidant. The reaction was characterized by various spectroscopic measurements and a kinetic analysis of O-2 evolution. X-ray diffraction (XRD) data indicates the interlayer separation of mica changes upon intercalation of 1. The UV-vis diffuse reflectance (RD) and Mn K-edge X-ray absorption near-edge structure (XANES) data suggest that the oxidation state of the di-mu-oxo Mn-2 core is Mn-III-Mn-IV, but it is not intact. In aqueous solution, the reaction of 1 with a large excess CeIV oxidant led to decomposition of 1 to form MnO4- ion without O-2 evolution, most possibly by its disproportionation. However, MnO4- - formation is suppressed by adsorption of 1 on clay. The maximum turnover number for O2 evolution catalyzed by 1 adsorbed on mica and kaolin was 15 and 17, respectively, under the optimum conditions. The catalysis occurs in the interlayer space of mica or on the surface of kaolin, whereas MnO4 - formation occurs in the liquid phase, involving local adsorption equilibria of adsorbed 1 at the interface between the clay surface and the liquid phase. The analysis of O-2 evolution activity showed that the catalysis requires cooperation of two equivalents of 1 adsorbed on clay. The second-order rate constant based on the concentration (mol g(-1)) of 1 per unit weight of clay was 2.7 +/- 0.1 mol(-1) s(-1) g for mica, which is appreciably lower than that for kaolin (23.9 +/- 0.4 mol-1 s-1 g). This difference can be explained by the localized adsorption of 1 on the surface for kaolin. However, the apparent turnover frequency (( k(O2)) (app)/s(-1)) of 1 on mica was 2.2 times greater than on kaolin when the same fractional loading is compared. The higher cation exchange capacity (CEC) of mica statistically affords a shorter distance between the anionic sites to which 1 is attracted electrostatically, making the cooperative interaction between adsorbed molecules of 1 easier than that on kaolin. The higher CEC is important not only for attaining a higher loading but also for the higher catalytic activity of adsorbed 1.

DOI： 10.1021/jp063679n

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

A [Ru(bpy)(3)](2+) (bpy=2,2'-bipyridine)-doped WO3 film was prepared as a base layer on a substrate by cathodic electrodeposition from a colloidal triad solution containing peroxotungstic acid (PTA), [Ru(bpy)(3)](2+), and poly(sodium 4-styrenesulfonate) (PSS). A Prussian blue (PB; Fe-II-Fe-III) film was cathodically electrodeposited on the [Ru(bpy)3]21 -doped WO3 film or neat WO3 film from an aqueous Berlin brown (BB; Fe-III-Fe-III.) colloid solution to yield a [Ru(bpy)(3)](2+)-doped WO3/PB bilayer film or WO3/PB bilayer film. For the spectrocyclic voltammogram (SCV) of the WO3/PB film, a redox response of Prussian white (PW; (FeFeII)-Fe-II)/PB was observed at 0.11 V, however, further oxidation of PB to BB was not allowed by the interfacial n-type Schottky barrier between the WO3 and PB layers. For the [Ru(bpy)(3)](2+)-doped WO3/PB film, any electrochemical response assigned to the redox of PB was not observed in the cyclic voltammogram, however, the in situ absorption spectral change recorded simultaneously showed the significant redox reactions based on PB. The SCV revealed that PW on the [Ru(bpy)3]2+ -doped WO3 film is completely oxidized to PB by a geared reaction of Ru-II/Ru-III at 1.05 V, and that 32 % of PB formed is further oxidized to BB by the same geared reaction in the potential scan to 1.5 V PB was completely re-reduced to PW by a geared reaction of HxWO3/WO3 at -0.5 V in the reductive potential scan. These geared electrochemical reactions produced an electrochromic hysteresis performance of the PB film layered on the [Ru(bpy)(3)](2+)-doped WO3 film.

DOI： 10.1002/chem.200600369

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

A [Ru(bpy)(3)](2+) (bpy=2,2'-bipyridine)-doped WO3 film was prepared as a base layer on a substrate by cathodic electrodeposition from a colloidal triad solution containing peroxotungstic acid (PTA), [Ru(bpy)(3)](2+), and poly(sodium 4-styrenesulfonate) (PSS). A Prussian blue (PB; Fe-II-Fe-III) film was cathodically electrodeposited on the [Ru(bpy)3]21 -doped WO3 film or neat WO3 film from an aqueous Berlin brown (BB; Fe-III-Fe-III.) colloid solution to yield a [Ru(bpy)(3)](2+)-doped WO3/PB bilayer film or WO3/PB bilayer film. For the spectrocyclic voltammogram (SCV) of the WO3/PB film, a redox response of Prussian white (PW; (FeFeII)-Fe-II)/PB was observed at 0.11 V, however, further oxidation of PB to BB was not allowed by the interfacial n-type Schottky barrier between the WO3 and PB layers. For the [Ru(bpy)(3)](2+)-doped WO3/PB film, any electrochemical response assigned to the redox of PB was not observed in the cyclic voltammogram, however, the in situ absorption spectral change recorded simultaneously showed the significant redox reactions based on PB. The SCV revealed that PW on the [Ru(bpy)3]2+ -doped WO3 film is completely oxidized to PB by a geared reaction of Ru-II/Ru-III at 1.05 V, and that 32 % of PB formed is further oxidized to BB by the same geared reaction in the potential scan to 1.5 V PB was completely re-reduced to PW by a geared reaction of HxWO3/WO3 at -0.5 V in the reductive potential scan. These geared electrochemical reactions produced an electrochromic hysteresis performance of the PB film layered on the [Ru(bpy)(3)](2+)-doped WO3 film.

DOI： 10.1002/chem.200600369

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Tetraphenylporphine zinc(II) (ZnTPP) was found to be adsorbed from its CH2Cl2 solution into a Nafion (Nf) film. The characteristics of the adsorption of ZnTPP into the Nf film were studied using a visible absorption spectroscopic technique. The initial rate (v(0), mol cm(-2) s(-1)) for uptake of ZnTPP was saturated with increasing ZnTPP concentration (c(0), M) in the solution. This kinetic profile was analyzed in terms of a Michaelis-Menten model considering preequilibrium of ZnTPP adsorption between the solution and the outer layer of the Nf film, followed by diffusion to an inner bulk region, giving a maximum diffusion reflux of v(max) = (2.2 +/- 0.2) x 10(-13) mol cm(-2) s(-1). This is different from the kinetics for the Nf/phthalocyanine zinc(II) (ZnPc) film, which gives a linear plot of v(0) vs c(0). This can be explained by the relatively slow diffusion of ZnTPP in the film compared to that of ZnPc because of steric factors: ZnTPP contains bulky tetraphenyl moieties attached perpendicular to a porphyrin ring, whereas ZnPc has higher planarity. The isotherm for the adsorption of ZnTPP into the Nf film was analyzed using a Langmuir isotherm equation, yielding an equilibrium constant of (3.6 +/- 1.1) x 10(6) M-1 and a saturated amount of adsorbed ZnTPP of (1.8 +/- 0.1) x 10(-9) mol cm(-2), suggesting monolayer adsorption of ZnTPP on the hydrophobic polymer network interfacial with hydrophilic transport channels without significant intermolecular overlap. This is in contrast to the multilayer adsorption mode suggested for the ZnPc adsorption. The tetraphenyl moieties could prevent the stacking of ZnTPP for multilayer adsorption.

DOI： 10.1021/jp061211e

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Language：English   Publishing type：Part of collection (book)   Publisher：SPRINGER-VERLAG BERLIN  

Polymeric materials confining functional molecules are one of the most promising materials for designing nanodevices for energy conversion, e.g., solar cells, fuel cells, and artificial photosynthetic devices that are expected to provide a renewable energy resource. Charge transport (CT) and catalysis by redox molecules in polymeric solid materials are reviewed with a focus on a polyanion film, typically Nafion and other polymeric materials, containing excess water. CT in a polyanion film is evaluated based on the physical displacement (physical diffusion) and charge hopping mechanisms between redox molecules. The mechanism of CT is exhibited to depend on the structure and redox reaction of the center molecules, and the influencing factor on CT is discussed. For the polymeric solid reactor containing excess water, the physical data of CT and molecular transport in the bulk matrix are summarized to demonstrate that the electrochemical reaction in the solid reactor occurs similarly as in an aqueous solution. Recent progress in molecular catalysis for multielectron redox reactions with a focus on water oxidation, reduction of proton, and carbon dioxide is introduced, and the catalytic activity and mechanism in solution and polymeric matrixes are reviewed. A dye-sensitized solar cell was fabricated using polymeric solid materials containing excess organic solution as an electrolyte layer, and its performance similar to a liquid-type solar cell is discussed based on the physicochemical data in the polymeric solid materials. Recent approaches toward construction of an artificial photosynthetic system are reviewed, and, finally, concluding remarks and directions for future research are given.

DOI： 10.1007/b136872

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

Electrochemical reactions of Ruthenium purple, Fe-4(III)[Ru-II(CN)(6)](3) (RP; Fe-III-Ru-II) were studied using a spectrocyclic voltammetry (SCV) technique. The SCV measurement for an RP film coated on an ITO electrode showed a reversible redox between RP and Ruthenium white (RW; Fe-II-Ru-II) at 0.14 V vs saturated calomel reference electrode (SCE). An RP film was electrode posited on a hybrid film of tungsten trioxide (WO3)/tris(2,2'-bipyridine)ruthenium(II) ([Ru(bpy)(3)](2+); bpy=2,2'-bipyridine)/poly(sodium 4-styrenesulfonate) (PSS) (denoted as WRP film) from a colloidal solution containing 0.5 mM FeCl3, 0.5 mM K-4[Ru(CN)(6)] and 40 mM KCl using a potentiodynamic multi-sweep technique. In a cyclic voltammogram (CV) of a WRP/RP film, a redox response was observed at 0.61 V in addition to essential redox responses of WRP hybrid film (a [Ru(bpy)(3)](2+)/[Ru(bpy)(3)](3+) redox at 1.03 V and a HxWO(3)/ WO3 redox below 0.09 V), but a redox response of RW/RP was not observed at 0.14 V. The SCV measurement for the WRP/RP film suggested that the redox response at 0.61 V is attributed to a redox of [Ru(bPY)(3)](2+)/[Ru(bpy)(3)](3+) interacted electrostatically with RP. it also showed that RW is oxidized to RP via [Ru(bpy)(3)](2+)/[Ru(bpy)(3)](3+) redox and RP is reversibly reduced to RW via HxWO3WO3 redox. This unique geared electrochemical reaction for the WRP/RP film leads to a hysteresis property of an RW/RP redox.

DOI： 10.1002/masy.200650321

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Phthalocyanine zinc(II) (ZnPc) was found to be adsorbed well into a Nafion (Nf) film. The kinetic analysis suggested that the adsorption of ZnPc into the Nf film is controlled by its diffusion in the Nf film with a diffusion coefficient of D = 1.9 x 10(-6) cm(2) s(-1) that is higher than those (10(-9)-10(-12) cm(2) s(-1)) of cationic redox molecules in the Nf film by 3-6 orders of magnitude. The adsorption isothermal was analyzed by a Brunauer-Emmett-Teller (BET) equation suggesting multilayer adsorption of ZnPc into the film. The BET analysis provided the amount of ZnPc for monolayer adsorption (w(m) = 1.50 x 10(-7) mol cm(-2)), from which the effective area for the ZnPc adsorption was estimated to be larger by a factor of 1.7 x 103 than the Nf film area (1.0 cm(2)). The absorption spectra of a Nf film adsorbing ZnPc ((Nf/ZnPc)(ads) film) exhibited two broad absorption bands at 385 and 680-750 nm without any structural features, which is significantly different from the absorption spectra of either ZnPc solution in DMF or a (Nf/ZnPc)(mix) film prepared from a DMF solution containing Nf and ZnPc by solvent evaporation. This is ascribed to the formation of a ZnPc aggregate in the (Nf/ZnPC)(ads) film. Photoluminescence data for the (Nf/ZnPc)(mix) film suggested the presence of a ZnPc monomer and dimer at equilibrium in the film with a concentration of 0.1 M and that energy transfer occurs from the monomer to the dimer in excitation of the monomer (at A x = 609 nm) to yield emission from the dimer. By contrast, photoluminescence data for the (Nf/ZnPc)(ads) film suggested that the excited ZnPc is self-quenched significantly by the formation of the ZnPc aggregate in the film. The lesser electroactivity of ZnPc in the (Nf/ZnPc)(ads) film compared with that in the (Nf/ZnPc)(mix) film could be ascribable to more difficult diffusion of ZnPc in the former film due to the formation of the ZnPc aggregate. The adsorption of ZnPc into the Nf film was significantly regulated by simple pretreatments of the Nf film such as immersion in solvents and storage under solvent vapors. The regulation was explained by controlled physical and chemical properties of a channel for mass and ion transport that is formed by sulfonate groups, countercations, and solvent molecules in the Nf film.

DOI： 10.1021/jp052218j

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Active catalysts for water oxidation to evolve O-2 are required for the construction of artificial photosynthetic devices that are expected to be promising energy-providing systems in the future. The citrate-stabilized IrO2 colloid was self-assembled onto an indium tin oxide (ITO) electrode to form a monolayer of the colloidal IrO2 particles when it was dipped in the colloid solution. The self-assembly could be achieved by a chemical interaction between carboxylate groups on the citrate stabilizer and hydroxyl groups on the ITO surface to form ester bonds. Efficient electrocatalysis for water oxidation was demonstrated using the electrode modified by the self-assembled IrO2 colloid to yield the highest turnover frequency ((2.3-2.5) x 10(4) h(-1)) of IrO2 in the hitherto-reported catalysts for electrochemical water oxidation.

DOI： 10.1021/jp0550208

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier  

A homogenous and transparent IrO2 film was prepared on an ITO electrode by anodic electrodeposition under galvanostatic conditions from an aqueous solution containing 2 mM K2IrCl6 and 40 mM oxalic acid that is aged at 37 °C and pH 10 for ca. 10 days. The absorption spectral change of the solution suggested that an IrO2 colloid is formed in the solution during ca. 10 day-aging. The scanning electron microscopic (SEM) measurement displayed homogeneous deposition of IrO 2 particles with 100-250 nm of a diameter on the surface of the film. The X-ray diffraction (XRD) measurement indicated that IrO2 in the film is amorphous. The cyclic voltammogram (CV) of the IrO2-coated ITO electrode dipped in a 0.1 M KNO3 aqueous solution exhibited a steep rise of an anodic current at 1.0 V vs SCE for catalytic water oxidation, as well as an anodic wave at 0.3 V and a corresponding cathodic wave at -0.1 V that are assigned as an IrIV/IrV redox. The anodic current at 1.3 V on the CV was 660 times higher than that for a blank bare ITO electrode. Ir electrodeposited on the ITO electrode was also shown to be electrocatalytically active for water oxidation. However, the anodic current at 1.3 V on the CV for the Ir-coated ITO electrode was 14 times lower than that for an IrO2-coated electrode in spite of the 34 times higher coverage of Ir. The potential static electrochemical water oxidation using the IrO2-coated ITO electrode produced a significant amount of O 2 above 1.1 V vs Ag/AgCl, in contrast to no O2 detected even at 1.3 V using a bare ITO electrode. The maximum turnover frequency (TOF) of the IrO2 catalyst was provided as 16,400 ± 450 h -1 at 1.3 V vs Ag/AgCl from the slope of the linear plots of the amount of O2 vs coverage of IrO2 in the range of ∼1.5 × 10-9 mol. The TOF was 450 times higher than that (36.4 ± 1.4 h-1 at 1.3 V) for electrodeposited Ir showing the very high catalytic activity of the IrO2 film. © 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jelechem.2005.01.030

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A homogenous and transparent IrO2 film was prepared on an ITO electrode by anodic electrodeposition under galvanostatic conditions from an aqueous solution containing 2 mM K2IrCl6 and 40 mM oxalic acid that is aged at 37 degrees C and pH 10 for ca. 10 days. The absorption spectral change of the solution suggested that an IrO2 colloid is formed in the solution during ca. 10 day-aging. The scanning electron microscopic (SEM) measurement displayed homogeneous deposition of IrO2 particles with 100-250 nm of a diameter on the surface of the film. The X-ray diffraction (XRD) measurement indicated that IrO2, in the film is amorphous. The cyclic voltammogram (CV) of the IrO2-coated ITO electrode dipped in a 0.1 M KNO3 aqueous solution exhibited a steep rise of an anodic current at 1.0 V vs SCE for catalytic water oxidation, as well as an anodic wave at 0.3 V and a corresponding cathodic wave at -0.1 V that are assigned as an Ir-IV/Ir-V redox. The anodic current at 1.3 V on the CV was 660 times higher than that for a blank bare ITO electrode. Ir electrodeposited on the ITO electrode was also shown to be electrocatalytically active for water oxidation. However, the anodic current at 1.3 V on the CV for the Ir-coated ITO electrode was 14 times lower than that for an IrO2-coated electrode in spite of the 34 times higher coverage of Ir. The potential static electrochemical water oxidation using the IrO2-coated ITO electrode produced a significant amount of O-2 above 1.1 V vs Ag/AgCl, in contrast to no O-2 detected even at 1.3 V using a bare ITO electrode, The maximum turnover frequency (TOF) of the IrO2 catalyst was provided as 16,400 450 h(-1) at 1.3 V vs Ag/AgCl from the slope of the linear plots of the amount of O-2 vs coverage of IrO2 in the range of similar to 1.5 x 10(-9) mol. The TOF was 450 times higher than that (36.4 +/- 1.4 h(-1) at 1.3 V) for electrodeposited Ir showing the very high catalytic activity of the IrO2 film. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jelechem.2005.01.030

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

A tungsten trioxide (WO3)/tris(2,2'-bipyridine)ruthenium(II) ([Ru(bPY)(3)](2+); bpy = 2,2'-bipyridine)/poly(sodium 4-styrenesulfonate) (PSS) hybrid film was prepared by electrodeposition from a colloidal triad solution containing peroxcitungstic acid (PTA), [Ru(bPY)(3)](2+), and PSS. A binary solution of [Ru(bpy)(3)](2+) and PTA (30 vol % ethanol in water) gradually gave an orange precipitate, possibly caused by the electrostatic interaction between the cationic [Ru(bPY)(3)](2+) and the anionic PTA. The addition of PSS to the binary PTA/[Ru(bpy)(3)](2+) solution remarkably suppressed this precipitation and caused a stable, colloidal triad solution to form. The spectrophotometric measurements and lifetime analyses of the photoluminescence from the excited [Ru(bPY)(3)](2+) ion in the colloidal triad solution suggested that the [Ru(bpy)(3)](2+) ion is partially shielded from electrostatic interaction with anionic PTA by the anionic PSS polymer chain. The formation of the colloidal triad made the ternary [Ru(bpy)(3)](2+)/PTA/PSS solution much more redox active. Consequently, the rate of electrodeposition of WO3 from PTA increased appreciably by the formation of the colloidal triad, and fast electrodeposition is required for the unique preparation of this hybrid film. The absorption spectrum of the [Ru(bpy)(3)](2+) ion in the film was close to its spectrum in water, but the photoexcited state of the [Ru(bPY)(3)](2+) ion was found to be quenched completely by the presence of WO3 in the hybrid film. The cyclic voltammogram (CV) of the hybrid film suggested that the [Ru(bpy)(3)](2+) ion performs as it is adsorbed onto WO3 during the electrochemical oxidation. An ohmic contact between the [Ru(bpy)(3)](2+) ion and the WO3 surface could allow the electrochemical reaction of adsorbed [Ru(bPY)(3)](2+). The composition of the hybrid film, analyzed by electron probe microanalysis (EPMA), suggested that the positive charge of the [Ru(bpy)(3)](2+) ion could be neutralized by partially reduced WO3 ions, in addition to Cl- and PSS units, based on the charge balance in the film. The electrostatic interaction between the WO3- ion and the [Ru(bpy)(3)](2+) ion might be responsible for forming the electron transfer channel that causes the complete quenching of the photoexcited [Ru(bpy)(3)](2+) ion, as well as the formation of the ohmic contact between the [Ru(bpy)(3)](2+) ion and WO3. A multicolor electrochromic performance of the WO3/[Ru(bpy)(3)](2+)/PSS hybrid film was observed, in which transmittances at 459 and 800 nm could be changed, either individually or at once, by the selection of a potential switch. Fast responses, of within a few seconds, to these potential switches were exhibited by the electrochromic hybrid film.

DOI： 10.1002/chem.200400323

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JOHN WILEY & SONS INC  

To develop better polymeric materials for optical-resolution membranes, we synthesized nine chiral phenylacetylenes containing pinanyl groups. We used them to investigate the effects of chemical structures, including the number and position of the chiral groups in the monomers, on the induction of chirality in the main chain during polymerization and on the degree of enantioselectivity in the permeation of the polymeric membranes. The monomers included six new chiral p-(oligomethylpinanylsiloxanyl)phenylacetylenes. The homopolymerizations of these nine monomers with a Rh complex produced high-molecular-weight polymers (molecular weight = 10(5)-10(6)). Of the five polymers with a chiral pinanyl group at the 1-position of each oligosiloxanyl group, all except for two polymers showed high molar ellipticity in the main-chain region in the circular dichroism spectra. This finding indicated that these polymers had a chiral helical main chain. The membranes fabricated from all the polymers synthesized in this study were high-quality, except for two polymers. All these membranes showed enantioselective permeabilities for two amino acids and an alcohol. The membranes from the polymers with a chiral helical backbone, a high content of pinanyl groups, no oligodimethylsiloxane moieties, or a combination of these showed good enantioselectivities ( = 1.7-640) in permeation. We propose that the sense of the main-chain helicity determined the selectivity. (C) 2004 Wiley Periodicals, Inc.

DOI： 10.1002/pola.20356

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

DOI： 10.1021/ja039780c

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Charge transport (CT) in a Nafion film incorporating [(NH3)(5)Ru(mu-pz)Ru(NH3)(5)](4+) ([Ru-II-Ru-II](4+); pz = pyrazine) was studied using a double potential-step chronoabsorptometry (DPSCA) technique. The oxidative CT by [Ru-II-Ru-II](4+)/[Ru-II-Ru-III](5+) (in a potential step from -0.2 to 0.3 V; first step) was compared with that by [Ru-II-Ru-III](5+)/[Ru-III-Ru-III](6+) (in a successive potential step from 0.3 to 0.7 V; second step). The predominant CTs by a physical displacement mechanism of the complexes were suggested for both of the steps. However, the rate constant of the CT for the first step was 5.2 time higher than that for the second step at 25 degreesC. The results on CT kinetics and dynamics revealed that the CTs in both of the steps are entropy-controlled in the activation at room temperature. The DeltaH(double dagger) (12 kJ mol(-1)) for the physical displacement in the second step was lower than that (24 kJ mol(-1)) for the first step, showing that the physical displacement for the second step is enthalpically favorable compared with that for the first step. The corresponding DeltaS(double dagger) (-234 J K-1 mol(-1)) for the second step is lower than that (DeltaS(double dagger) = -184 J K-1 mol(-1)) for the first step, making the physical displacement for the second step more entropically difficult than that for the first step. The entropy effect on the physical displacement was discussed on the basis of the interaction of the complexes with Nafion and reorganization of the solvent (water) molecule involved in the process. The DeltaS(double dagger) for the physical displacement of redox complexes in the film decreased with the positive charge of the complexes, suggesting that the highly positive-charged complex is entropically unfavorable for physical displacement, presumably due to higher degree of solvation of the complex and the sulfonate groups in their dissociation.

DOI： 10.1021/jp036146c

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Charge transport (CT) in a Nafion film incorporating [Ru(bpz)(3)](2+) (bpz = 2,2'-bipyrazine) was investigated using a potential-step chronocouloabsorptometry technique. The reductive CT by [Ru(bpz)(3)](2+/+) was found to take place by a combination mechanism of physical displacement of the complex and charge hopping between the molecules of the complex. This is a different mechanism from that of the oxidative CT (occurring by a charge hopping mechanism) in an earlier reported Nafion/[Ru(bpy)(3)](2+/3+) (bpy = 2,2'-bipyridine) system. The combination mechanism in CT was also reported in an earlier Nafion/[(NH3)(5)Ru-O-Ru(NH3)(4)-O- Ru(NH3)(5)](6+) (Ru-red) system. In the present [Ru(bpz)(3)](2+) system, the activation energy (E-a = 78 kJ.mol(-1)) of physical displacement is higher than that (40 kJ-mol(-1)) of charge hopping. In the Ru-red system, on the contrary, the Ea (13 kJ.mol(-1)) of physical displacement is lower than that (55 kJ-mol(-1)) of charge hopping. As a result, the fraction (Phi(c)) of the contribution of charge hopping to the initial CT rate decreased with increasing temperature for the [Ru(bpz)(3)](2+) System, whereas it increased with increasing temperature for the Ru-red system. The physical displacement was enthalpy-controlled in the [Ru(bpZ)(3)](2+) system at 25 degreesC. By contrast, it was entropy-controlled in the Ru-red system. The featured factors influencing physical displacement and charge hopping were discussed.

DOI： 10.1021/jp026859f

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DOI： 10.1021/jp026859f

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A first and unique preparation is reported of a WO3/tris(2,2'-bipyrizine)ruthenium (II) (Ru(bpy)(3)(2-)) composite film by electrodeposition from a colloidal solution containing peroxotungstic acid and Ru(bpy)(3)(2+) that is remarkably stabilized by poly(sodium 4-styrensulfonate). The composite film clearly demonstrated multiple electrochromism. The photoexcited Ru(bpy)(3)(2+) was found to be quenched completely by WO3 in the composite film, which is responsible for an electronic interaction of Ru(bpy)(3)(2+) with WO3. The complete quenching led to a photocharging-discharging character and a steady-state photoanodic current induced by visible light.

DOI： 10.1021/jp0257606

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Charge transport (CT) in a Nafion membrane containing mu-oxobis[aquabis(2.2'-bipyridine)ruthenium(III)] complex. [(bpy)(2)(H2O)Ru-O-Ru(H2O)(bpy)(2)](4+) (bpy = 2.2'-bipyridine. abbreviated to Ru-III -O-Ru-III) was investigated by potential-step chronocoulospectrometry (PSCCS). Electrochemical reduction of Ru-III-O-Ru-III in the membrane occurred irreversibly to form [Ru(bpy)(2)(OH2)(2)](2+) monomer. The CT by reduction of Ru-III-O-Ru-III. in the membrane was suggested to take place by physical displacement of the complex, which is quite different from the mechanism in the CT by oxidation of Ru-III-O-Ru-III in the same membrane in which charge is transported by charge hopping based on reversible redox reaction between Ru-III-O-Ru-III and Ru-III-O-Ru-IV. The fractions of the electrochemically reacted complex in the membrane for the oxidative CT was dependent on the complex concentration, and the yield was low (maximum fraction = 0.42 at 0.87 M) relative to the reductive CT. By contrast. the fraction for the reductive CT was independent of the concentration over 0.12 M and close to unity. The different concentration dependence of the fraction was discussed related to the difference in the CT mechanism. (C) 2002 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0013-4686(02)00105-6

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Language：English   Publisher：AMER CHEMICAL SOC  

DOI： 10.1021/cr980108l

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

DOI： 10.1002/1521-3773(20010803)40:15<2925::AID-ANIE2925>3.0.CO;2-7

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

Catalytic activity of a dinuclear ammine ruthenium complex, [(NH3)(5)Ru-O-Ru(NH3)(5)](4+), for water oxidation to evolve O-2 was investigated both in homogeneous aqueous solution and in heterogeneous Nafion(R) membrane systems using Ce-IV oxidant. It was suggested that the complex works as a four-electron water oxidation catalyst and that the water oxidation by the complex is in competition with a bimolecular decomposition between the complexes. The first-order rate constant (k(O2) (s(-1)) for O-2 evolution and second-order rate constant (k(deact) (M-1 s(-1))) for bimolecular decomposition were obtained by a kinetic analysis. It was found that k(deact) decreased by one order of magnitude by incorporating the complex in the membrane; this was ascribed to the suppression of the bimolecular decomposition. The critical decomposition distance (Td (nm)) between the catalysts was analyzed to be 1.06 nm based on an intermolecular distance distribution.

DOI： 10.1246/bcsj.73.2193

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Photosynthesis produces molecular oxygen from water catalyzed by an enzyme whose active site contains a tetramanganese-oxo core of incompletely established structure. The first functional mimic of this core has been synthesized containing a cubical [Mn4O4](n+) core, surrounded by six facially bridging bidentate chelates to the manganese ions ((dpp)(6)Mn4O4 (1); dpp(-) = diphenylphosphinate anion). Bond enthalpy data predict that the Mn4O46+ core is thermodynamically capable of releasing molecular O-2, but is kinetically prevented from doing so by an activation barrier. UV light absorption into a Mn-O charge-transfer excited state (but not excitation of a Mn ligand-field excited state) efficiently releases an O-2 molecule if performed in the gas phase and concomitantly releases a bridging dpp- anion and the cationic species (dpp)(5)Mn4O2+ (presumed Mn4O2-butterfly core type). All species were identified by high resolution mass spectrometry. This reaction proceeds with high quantum efficiency (&gt;50%) and is the only observable reaction channel. The O-2 product derived exclusively from the corner ore's of the cube based on photochemistry of the O-18-isotopomer, ((dpp)(6)Mn-4(O-18)(4) Neither O-2 release nor dpp- dissociation are observed individually to occur in the excited state, indicating that O-O bond formation and O-2 release require dissociation of one of the six dpp- chelates ("Jack-in-the-Box" mechanism for O-2 formation). By contrast, neither O-2 production nor chelate photodissociation are observed in condensed phases, presumably due to either quenching of the photoexcited state or rapid recombination of dpp- and (dpp)(5)Mn4O4+ in the solvent cage. Previous results show that chemical reduction of (1) in solution using hydrogen atom donors produces the deoxygenated (dpp)(6)Mn4O2 core and releases two water molecules as the only products. Thus the [Mn4O4](n+) cubane core is an intrinsically reactive core topology that facilitates both the selective chemical reduction of two of the four oxygen atom bridges to water molecules and their photorearrangement to an O-2 molecule under the control of chelation of the manganese ions by dpp-. These results may offer insight into the possible nature of the photosynthetic O-2-evolving mechanism.

DOI： 10.1021/ja0005587

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cis-Tetraamminedichlororuthenium(III) (cis-[Ru(NH3)(4)Cl-2](+)) complex was found to work as a very active water oxidation catalyst to evolve dioxygen (O-2) in an aqueous solution as well as in a Nafion membrane. The initial O-2 evolution rate (V-o2, (mol s(-1))) was first-order with respect to the complex concentration in both the solution and membrane. The catalyst undergoes a bimolecular decomposition to deactivate at high complex concentrations. The first-order rate constant (k(o2) (s(-1))) for O-2 evolution and the second-order rate constant (k(deact) (dm(3) mol(-1) s(-1))) for bimolecular decomposition were obtained from the kinetic analysis based on the competition between both processes. The k(o2) (1.4 x 10(-2) s(-1)) in the Nafion membrane is much higher than that (2.3 x 10(-3) s(-1)) in the solution. The k(deact) (5.1 x 10(-1) dm(3) mol(-1) s(-1)) in the membrane was slightly higher than that (2.0 x 10(-1) dm(3) mol(-1) s(-1)) in the solution, The catalytic activity in the Nafion membrane was analyzed in terms of the intrinsic activity (k(o2) (s(-1))) and critical decomposition distance (r(d) (nm)) on the basis of the intermolecular distance distribution to obtain k(o2) = 1.5 x 10(-2) s(-1) and r(d) = 0.88 nm. The k(o2) was compared with the earlier results on [Ru(NH3)(6)](3+) and [Ru(NH3)(5)Cl](2+); the k(o2) of the complexes was in the order cis-[Ru(NH3)(4)Cl-2](+) &gt; [Ru(NH3)(5)Cl](2+) &gt; [Ru(NH3)(6)](3+). The structural effect on the catalytic activity was discussed.

DOI： 10.1021/jp991776t

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The catalytic activity of a trinuclear Ru complex; ([(NH3)(5)Ru-O-Ru(NH3)(4)-O-Ru(NH3)(5)](6+)) (Ru-red) for water oxidation was investigated both in a homogeneous aqueous solution system (AS) and a heterogeneous montmorillonite adsorbed system (clay). It was shown that water oxidation by the catalyst in the clay to evolve O-2 is a competitive reaction with bimolecular decomposition of the catalyst. The bimolecular decomposition was remarkably suppressed in the clay as compared with the aqueous solution, and the catalytic activity was maintained under higher concentration conditions. This was ascribed to the immobilization and isolation of the complex in the clay. The catalytic activity was analyzed by a model equation based on intermolecular distance distribution of the complex. The catalytic activity (k(O2)) and the critical decomposition distance (r(d)) were obtained as 1.7 x 10(-2) s(-1) and 2.39 nm, respectively. (C) 2000 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S1381-1169(99)00348-9

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The activity of tris(ethylenediamine)ruthenium (III) complex, [Ru(en)(3)](3+), as a water oxidation catalyst was studied in a homogeneous aqueous solution and a heterogeneous Nafion (Nf) membrane. In the aqueous solution, the apparent catalytic activity (k(app) (s(-1))) decreased monotonously with the concentration due to a bimolecular decomposition of the complex. The bimolecular decomposition of the complex was remarkably suppressed by incorporating it into a Nf membrane. An optimum complex concentration for k(app) in the Nf membrane was exhibited, which was explained both by a cooperative catalysis and a bimolecular decomposition of the complex. The k(app) in the Nf membrane was analyzed in terms of an intrinsic catalytic activity (k(O2) (s(-1))) of the complex, a cooperative catalysis distance (r(co) (nm)) and a critical decomposition distance (r(d) (nm)) between them based on intermolecular distance distribution to obtain the k(O2) = 8.5 x 10(-5) s(-1) r(co) =1.44 nm and r(d) =1.07 nm. The results in the [Ru(en)(3)](3+) system were compared with those obtained in the [RU(NH3)(6)](3+) system. (C) 2000 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S1381-1169(99)00241-1

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Charge transport in a Nafion(R) membrane incorporating zinc(II) phthalocyanine (ZnPc) was studied using spectrocyclic voltammetry (SCV) and potential-step chronocoulospectrometry (PSCCS) techniques. The visible absorption spectra of the membrane depended on the ZnPc concentration in the membrane, showing the formation of the ZnPc dimer. The equilibrium constant between the monomer and dimer of ZnPc in the membrane was calculated as 75 M-1. Tt was found that the charge transport occurs by two processes; the first process was considered to be the charge injection from the electrode to the ZnPc present in close proximity to the electrode, and the second one, bulk charge transport in the membrane. The apparent rate constant for the presumed charge injection was estimated as 1.6 x 10(-2) s(-1). The bulk charge transport in the membrane was analyzed as a combination of a physical displacement of ZnPc and charge hopping between them considering the equilibrium between the monomer and dimer of ZnPc. This analysis shows that the charge transport takes place by physical displacement of the ZnPc monomer and not by charge hopping, and that the contribution of the dimer to the charge transport is negligible. The first order rate constant (k(p)) of the physical displacement of the ZnPc monomer was estimated as 3.3 x 10(-3) s(-1). The saturated fraction of the oxidized ZnPc in the membrane decreased with the ZnPc concentration in the membrane because of the bulk charge transfer decreased by the formation of the ZnPc dimer. (C) 2000 Elsevier Science S.A. All rights reserved.

DOI： 10.1016/S0022-0728(99)00488-X

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Electrocatalytic water oxidation was carried out using a basal-plane pyrolytic graphite (BPG) electrode coated with electrodeposited Platinum black (pt-black) adsorbing [Ru(NH3)(5)CI](2+) The amount of O-2 evolved (V-O2, mol h(-1)) remarkably increased by adsorbing the complex onto Pt-black. The plots of V-O2 vs, the complex amount on the Pt-black gave a sigmoidal curve, which was explained by both the cooperative catalysis by two molecules of the complex and their bimolecular decomposition. The electrocatalytic activity of the complex was analyzed in terms of its intrinsic activity, k (h(-1)), cooperative catalysis distance, r(infinity) (nm) and critical decomposition distance, r(d) (nm) for both the void space adsorption model (VAM) and surface adsorption model (SAM) based on intermolecular distance distribution. k = 940 h(-1) r(infinity) = 1.21 nm and r(d)= 0.97 nm for VAM and 950 h(-1) r(infinity) = 0.82 nm and r(d) = 0.78 nm for SAM were obtained, respectively. Remarkable high intrinsic activities are ascribed to the efficient charge transfer from the electrode to the complex attached to the Pt-black. (C) 1999 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S1381-1169(99)00201-0

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The temperature dependence of a charge transport rate, nu(CT) (mol dm(-3) s(-1)) in a Nafion(R) membrane incorporating a trinuclear ruthenium complex, Ru-red ([(NH3)(5)Ru-O-Ru(NH3)(4)-O-Ru(NH3)(5)](6+)) was studied using potential-step chronocoulospectrometry (PSCCS). The nu(CT) increased with increasing complex concentration and temperature. It was found from the analysis of the nu(CT) that the charge transport takes place by both physical displacement and charge hopping, and the first-order rate constant (k(1) (s(-1))) for the physical displacement and the second-order rate constant (k(2) (mol(-1) dm(3) s(-1))) for the charge hopping were obtained. The k(2) increased by one order of magnitude for a temperature increase from 5 to 35 degrees C, but k(1) increased only by a factor of 1.6. Both the physical displacement and charge hopping in the membrane are of the Arrhenius type, and the activation energy, E-a (55 +/-11 kJ mol(-1)), for the charge hopping was much larger than that (13 +/- 5 kJ mol(-1)) for the physical displacement. It was suggested from the discussion on the other activation parameters that the physical displacement is entropy-controlled, but the charge hopping is enthalpy-controlled at room temperature. (C) 1999 Elsevier Science S.A. All rights reserved.

DOI： 10.1016/S0022-0728(99)00382-4

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DOI： 10.1021/la9901985

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Language：Japanese   Publisher：The Society of Polymer Science, Japan  

DOI： 10.1295/kobunshi.48.525

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Water oxidation catalysis by [(bpy)(2)(H2O)Ru-O-Ru(H2O)(bpy)(2)](4+) (Ru-III(OH2)-O-Ru-III(OH2)) complex was studied in a homogeneous aqueous solution (AS) as well. as heterogeneous Nafion membrane (HM) using Ce(IV) oxidant. The initial O-2 evolution rate, V-O2 (mol s(-1)) increased linearly at low complex concentrations under the excess Ce(IV) oxidant, showing that 4-electron water oxidation is catalyzed by one molecule of the complex. The intrinsic catalytic activities, k(O2) (s(-1)), in the AS and HM were 4.2 X 10(-3) s(-1) and 2.4 X 10(-3) s(-1), respectively. These values are much higher than those of well-known metal and metal oxide catalysts. Comparison of catalytic activity for various metal complexes and oxides is presented. (C) 1999 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S1381-1169(98)00334-3

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The activity of an electrochemical water oxidation catalyst based on pentaamminechlororuthenium(III) ([Ru(NH3)(5)Cl](2+)) complex incorporated in an electrode-coated Nafion membrane was investigated. The complex worked as an active electrochemical catalyst, and an optimum concentration for the turnover number (TN) of the catalyst in the O-2 evolution was exhibited. The TN increased with the concentration at low concentrations, which was ascribed either to charge transfer between the catalysts or to cooperative catalysis by the complex. The TN decrease at high concentrations was ascribed to bimolecular decomposition of the catalyst. The catalyst activity (TN) was analyzed in terms of a charge transfer distance between the catalysts (r(0)/nm), a cooperative catalysis distance by the complex (r(co)/nm), and a critical decomposition distance of the catalyst (r(d)/nm) based on intermolecular distance distribution. It was suggested that the activity was controlled mainly by r(co) and r(d), and the values r(co) = 1.26 nm and r(d) = 0.82 nm were obtained. (C) 1999 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S1381-1169(98)00281-7

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Activity of hexaammineruthenium(III) complex ([RU(NH3)(6)](3+)) as a Water oxidation catalyst was investigated in a homogeneous aqueous solution (AS) as well as in a heterogeneous Nafion membrane (HM). In the AS, the apparent catalytic activity (k(app)/s(-1)) decreased monotonically with the concentration, which was ascribed to a bimolecular decomposition of the complex at high concentrations. The bimolecular decomposition was suppressed remarkably by incorporating the complex into the membrane. It was shown that 4-electron water oxidation is cooperatively catalyzed by two molecules of the complex in the membrane. The k(app) in the HM was much higher than that in the AS at the whole concentration range, which was ascribed both to a favorable interaction for the cooperative catalysis and to the suppression of the bimolecular decomposition by immobilization of the complex. The k(app) was analyzed in terms of an intrinsic activity (k(O2)/s(-1)) of the complex, cooperative catalysis distance (r(co)/nm) and critical decomposition distance (r(d)/nm) between them based on the intermolecular distance distribution to give k(O2) = 3.5 x 10(-5) s(-1), r(co) = 1.21 nm, and r(d) = 0.82 nm. These values were discussed and compared with those obtained in the pentaamminechlororuthenium(III) complex ([Ru(NH3)(5)Cl](2+)) system.

DOI： 10.1021/jp982688w

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Charge transport in a Nafion membrane incorporating a mu-oxobis[aqabis(2,2'-bipyridine)ruthenium(III)] complex, [(bpy)(2)(H2O)Ru-O-Ru(H2O)(bpy)(2)](4+) [abbreviated to Ru-III(OH2)-O-Ru-III(OH2)], was studied by using a potential-step chronocoulospectrometry (PSCCS), The oxidation of Ru-III(OH2)-O-Ru-III(OH2) to Ru-III(OH2)-O-Ru-IV(OH) was observed on a potential-step from 0 V vs. SCE to 1.0 V in the PSCCS measurement. The charge transport rate, mu(CT), is remarkably depended on the complex concentration. The analysis showed that the charge propagation takes place by charge hopping, whose rate constant is dependent on the complex concentration. Charge hopping distance between the complexes in the membrane was analyzed to be 1.09 nm based on an intermolecular distance distribution between them. (C) 1999 Elsevier Science Ltd. All rights reserved.

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Electrocatalytic water oxidation was carried out using a basal-plane pyrolytic graphite (BPG) electrode coated with electrodeposited Au particles adsorbing Ru-red ([(NH3)(5)Ru-O-Ru(NH3)(4)-O-Ru(NH3)(5)](6+)). The amount of O-2 evolved, V-O2 (mol h(-1)), increased remarkably by adsorbing the complex onto Au particles. The plots of V-O2 versus the complex amount on Au particles gave an almost straight line at its: low surface coverage, but deviated downward with an increase in its amount, which is ascribed to the bimolecular decomposition. The intrinsic turnover number (TN) of the complex is larger than that of the Au particle by three orders of magnitude, The catalytic activity of the complex was analyzed in terms of its intrinsic TN, k (h(-1)) and critical decomposition distance, r(d) (nm) based on intermolecular distance distribution to obtain k = 21.4 h(-1) and r(d) = 1.11 nm. (C) 1999 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0013-4686(98)00379-X

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Charge transport in a Nafion membrane incorporating a mu-oxobis[aqabis(2,2'-bipyridine)ruthenium(III)] complex, [(bpy)(2)(H2O)Ru-O-Ru(H2O)(bpy)(2)](4+) [abbreviated to Ru-III(OH2)-O-Ru-III(OH2)], was studied by using a potential-step chronocoulospectrometry (PSCCS), The oxidation of Ru-III(OH2)-O-Ru-III(OH2) to Ru-III(OH2)-O-Ru-IV(OH) was observed on a potential-step from 0 V vs. SCE to 1.0 V in the PSCCS measurement. The charge transport rate, mu(CT), is remarkably depended on the complex concentration. The analysis showed that the charge propagation takes place by charge hopping, whose rate constant is dependent on the complex concentration. Charge hopping distance between the complexes in the membrane was analyzed to be 1.09 nm based on an intermolecular distance distribution between them. (C) 1999 Elsevier Science Ltd. All rights reserved.

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Charge transfer in a Nafion membrane incorporating a trinuclear ruthenium complex. Ru-red ([(NH3)(5)Ru(mu-O)Ru(NH3)(4)(mu-O)Ru(NH3)(5)](6+)), was studied using potential-step chronoamperospectrometry (PSCAS). Reversible oxidation of Ru-red (Ru-III-Ru-IV-Ru-III) to Ru-brown (Ru-IV-Ru-III-Ru-IV) was observed under a potential-step from 0 to 0.5 V vs. SCE in the PSCAS measurement. The charge transport rate by the oxidation of Ru-red to Ru-brown in the membrane depended on the complex concentration and was analyzed by both the physical displacement of the complexes and charge hopping between them. It was found that the charge transport takes place in the membrane by both the physical displacement and charge hopping. The charge transfer distance was analyzed based on a intermolecular distance distribution between the redox centers, and the real charge hopping distance was estimated to be 1.1 nm. (C) 1999 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0013-4686(98)00351-X

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Electrocatalytic water oxidation was studied for an artificial oxygen evolving center (OEC) model using Nafion (Nf) membrane-coated electrode incorporating Ru-red ([(NH3)(5)Ru-O-Ru(NH3)(4)-O-RU(NH3)(5)](6+)) and an amino acid residue model compound. On the cyclic voltammogram (CV) of Ru-red in the presence of a Tyr residue model, p-cresol (p-Cre) or a His residue model, 4-methylimidazole (MIm), the anodic current in an oxidative scan is much higher than that without the model compounds. The amount of O-2 evolved in the potentiostatic electrolysis increased remarkably in the presence of p-Cre or MIm. The enhancing effect of the model compounds on the catalytic activity was analyzed in terms of the intrinsic activity, charge-transfer distance between the complexes, and their critical decomposition distance based on the intermolecular distance distribution. The charge-transfer distance was remarkably prolonged from 1.28 to 2.25 nm by the presence of p-Cre and to 1.60 nm by Mim, which strongly suggests that p-Cre and MIm work as mediators for charge transfer in an artificial OEC model.

DOI： 10.1021/ma980415t

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The temperature dependence of the charge transport rate (vCT (mol dm-3 s-1)) in a Nafion membrane incorporating Ru(bpy)2+ 3 (bpy = 2,2′-bipyridine) was investigated using potential-step chronocoulospectrometry (PSCCS). vCT increased with increasing the complex concentration as well as the temperature. The charge transport was analyzed by a combined process of physical displacement of the complexes and charge hopping between them. The second order rate constant (k2 (mol-1 dm3 s-1)) for the charge hopping in the membrane prepared by an adsorption method, in which the complex is adsorbed from its aqueous solution into a precoated Nafion membrane, is much larger than that in a mixture casting method in which an alcoholic solution of Nafion and the complex was cast on the electrode. Activation parameters were obtained in both the mixture casting and the adsorption systems. The much larger activation entropy for the charge hopping in the adsorption system compared to the mixture casting one was interpreted by the increase in the local complex concentration in the membrane by the adsorption method, which results in a larger k2 compared to the mixture casting system. © 1998 Elsevier Science S.A. All rights reserved.

DOI： 10.1016/S0022-0728(98)00044-8

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The temperature dependence of the charge transport rate (upsilon(CR) (mol dm(-3) s(-1))) in a Nafion membrane incorporating Ru(bpy)(3)(2+) (bpy = 2,2'-bipyridine) was investigated using potential-step chronocoulospectrometry (PSCCS). upsilon(CR) increased with increasing the complex concentration as well as the temperature. The charge transport was analyzed by a combined process of physical displacement of the complexes and charge hopping between them. The second order rate constant (k(2) (mol(-1) dm(3) s(-1))) for the charge hopping in the membrane prepared by an adsorption method, in which the complex is adsorbed from its aqueous solution into a precoated Nafion membrane, is much larger than that in a mixture casting method in which an alcoholic solution of Nafion and the complex was cast on the electrode. Activation parameters were obtained in both the mixture casting and the adsorption systems. The much larger activation entropy for the charge hopping in the adsorption system compared to the mixture casting one was interpreted by the increase in the local complex concentration in the membrane by the adsorption method, which results in a larger k(2) compared to the mixture casting system. (C) 1998 Elsevier Science S.A. All rights reserved.

DOI： 10.1016/S0022-0728(98)00044-8

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An ITO electrode was coated by a Nafion® film incorporating Ru(bpy)2+ 3 complex as a redox center. An amino acid residue model compound, either 3-methylindole as a tryptophan model, 4-methylimidazole as a histidine model, or p-cresol as a tyrosine model, was dispersed in the polymer matrix to study its effect on the charge transport by the complex with a potential-step chronoamperospectrometry (PSCAS) method from 0 to 1.3 V (vs. SCE). The results showed that the model compound increased the fraction of the Ru(bpy)2+ 3 which was electroactive, and this was ascribed most probably to the mediation effect of the model molecule on the charge hopping between the redox centers. Assuming a random distribution of the complex and the model molecule in the polymer matrix, the charge transfer distance by hopping was estimated to be 1.6 nm in the absence of a mediator, but a long-range charge transport distance was 2.2 nm in the presence of 3-methylindole, 2.0 nm in the presence of 4-methylimidazole, and 2.3 nm in the presence of p-cresol. © 1998 Elsevier Science S.A. All rights reserved.

DOI： 10.1016/S0022-0728(97)00540-8

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An ITO electrode was coated by a Nafion(R) film incorporating Ru(bpy)(3)(2+) complex as a redox center. An amino acid residue model compound, either 3-methylindole as a tryptophan model, 4-methylimidazole as a histidine model, or p-cresol as a tyrosine model, was dispersed in the polymer matrix to study its effect on the charge transport by the complex with a potential-step chronoamperospectrometry (PSCAS) method from 0 to 1.3 V (vs. SCE). The results showed that the model compound increased the fraction of the Ru(bpy)(3)(2+) which was electroactive, and this was ascribed most probably to the mediation effect of the model molecule on the charge hopping between the redox centers. Assuming a random distribution of the complex and the model molecule in the polymer matrix, the charge transfer distance by hopping was estimated to be 1.6 nm in the absence of a mediator, but a long-range charge transport distance was 2.2 nm in the presence of 3-methylindole, 2.0 nm in the presence of 4-methylimidazole, and 2.3 nm in the presence of p-cresol. (C) 1998 Elsevier Science S.A. All rights reserved.

DOI： 10.1016/S0022-0728(97)00540-8

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Redox reaction and charge transport of trinuclear ruthenium complex, Ru-red ([(NH3)(5)Ru(mu-O)Ru(NH3)(4)(mu-O)Ru(NH3)(5)](6+)) were investigated in a Nafion (Nf) membrane as well as in a homogeneous aqueous solution using a potential-step chronoamperospectrometry (PSCAS) in addition to a cyclic voltammetry (CV). It has been shown in CV that Ru-red is oxidized to Ru-brown and then oxidatively transforms to stable redox species in the membrane during repetitive cyclic scans. In a potential-step from 0 to 0.5 V (vs SCE) in PSCAS, a reversible oxidation of Ru-red to Ru-brown was observed in both the membrane and solution. The charge transport based on Ru-red/Ru-brown took place in the membrane by both physical displacement of the complex and charge hopping between them, while in the aqueous solution charge was transported only by physical displacement of the complex. In a potential-step from 0.5 to 1.5 V (vs SCE); an irreversible oxidative transformation of Ru-brown takes place to produce the species which has almost no absorption in the visible region. The transformed species were stable and redox active in the membrane. (C) 1998 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0013-4686(98)00080-2

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Redox reactions of tris(2,2′-bipyridine)ruthenium (II) (Ru(bpy)2+ 3) as well as charge transport in a Nafion® membrane were investigated using potential-step chronocoulospectrometry (PSCCS). The concentration of oxidized Ru(III) obtained from coulometric data was higher than that obtained from spectrophotometric changes, showing that the amount of charge passed does not correspond quantitatively to a real change of the redox center in the electrochemical reaction. Both the charge transport rates obtained from the spectrophotometric and coulometric data were analyzed by a combined process of a physical displacement and charge hopping. It was shown that charge hopping between the complexes takes place predominantly to transport charges in the membrane
the second order rate constant (6.0 × 10-1 M-1 s-1) of the charge hopping obtained from the coulometric data was twice that (2.5 × 10-1 M-1 s-1) calculated from the spectrophotometric data. © 1997 Elsevier Science S.A.

DOI： 10.1016/S0022-0728(97)00328-8

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Redox reactions of tris(2,2'-bipyridine)ruthenium (II) (Ru(bpy)(3)(2+)) as well as charge transport in a Nafion(R) membrane were investigated using potential-step chronocoulospectrometry (PSCCS). The concentration of oxidized Ru(III) obtained from coulometric data was higher than that obtained from spectrophotometric changes, showing that the amount of charge passed does not correspond quantitatively to a real change of the redox center in the electrochemical reaction. Both the charge transport rates obtained from the spectrophotometric and coulometric data were analyzed by a combined process of a physical displacement and charge hopping. It was shown that charge hopping between the complexes takes place predominantly to transport charges in the membrane; the second order rate constant (6.0 x 10(-1) M-1 s(-1)) of the charge hopping obtained from the coulometric data was twice that (2.5 x 10(-1) M-1 s(-1)) calculated from the spectrophotometric data. (C) 1997 Elsevier Science S.A.

DOI： 10.1016/S0022-0728(97)00328-8

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Photoelectrocatalytic water oxidation was investigated using a multilayer-modified electrode composed of a Nafion (Nf)) membrane incorporating tris(2,2'-bipyridine)ruthenium(II) ([Ru(bpy)(3)](2+)) sensitizer and an electrodeposited platinum black (Pt-black) adsorbing trinuclear ruthenium complex (Ru-red) ([(NH3)(5)Ru(mu-O)Ru (NH3)(4)(mu-O)Ru(NH3)(5)](6+)) as a water oxidation catalyst. In this multilayered indium tin oxide (ITO)/Nf [Ru(bpy)(3)(2+)]/Pt-black[Ru-red] system, an anodic photocurrent was generated induced by photoexcitation of [Ru(bpy)(3)](2+). This anodic photocurrent was much higher than that generated without Ru-red. Dioxygen evolution was also induced by visible light at anodic applied potentials, which was ascribed to rapid transfer of positive charge from [Ru(bpy)(3)](3+) to Ru-red where water oxidation takes place.

DOI： 10.1039/a702661g

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Activity of a pentaamminechlororuthenium(III) ([Ru(NH3)(5)Cl](2+)) complex as a water oxidation catalyst was investigated in a homogeneous aqueous solution (AS) as well as in a heterogeneous Nafion membrane (HM), In the AS, the apparent catalytic: activity (k(app)/s(-1)) decreased monotonically with the concentration. In competition with water oxidation catalysis, dinitrogen (N-2) evolution by oxidation of its ammine ligands was also observed, whose rate is second order with respect to its concentration, showing that a bimolecular decomposition of the complexes takes place at high concentrations, The bimolecular decomposition was suppressed remarkably by incorporating the complex into a HM. In the HM, k(app) increased with the catalyst concentration at low concentrations below 1.5 x 10(-2) M, indicating that four-electron water oxidation is cooperatively catalyzed by two complex molecules. The k(app) was strikingly higher for HM than for AS in the whole concentration range, which was ascribed to both a favorable interaction for the cooperative catalysis and the suppression of the bimolecular decomposition by immobilization of the complex. The effect of intermolecular distance distribution of the complex in the membrane on k(app) was analyzed in terms of cooperative catalysis distance (r(co)/nm) and critical decomposition distance (r(d)/nm) to give r(co) = 1.21 nm and r(d) = 0.84 nm. The r(co) value obtained might suggest cooperative catalysis through hydrogen bonds between water and ammine ligands.

DOI： 10.1021/jp963866t

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The activity of an electrocatalytic oxygen evolving center (OEC) molecule based on the trinuclear Ru complex, Ru-red ([(NH3)(5)Ru-O-Ru(NH3)(4)-O-Ru(NH3)(5)](6+)) codispersed with an amino acid residue model compound in a Nafion membrane was studied. The activity of the OEC molecule increased remarkably in the presence of p-cresol (p-Cre), a Tyr model compound. The activity was analyzed based on the intermolecular distance distribution in terms of charge transfer distances between the OEC molecules mediated by p-Cre, their critical decomposition distance, and the intrinsic activity. The charge transfer distance increased remarkably from 1.28 to 2.25 nm by the presence of p-Cre, suggesting that p-Cre works as a mediator for the charge transfer.

DOI： 10.1021/jp9638292

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A highly active electrocatalytic system to oxidise water to dioxygen (O-2) has been established using electrodeposited platinum black with an adsorbed trinuclear ruthenium complex (Ru-red). The catalyst turnover number for O-2 evolution was 1500 h(-1), four orders of magnitude greater than that of neat Pt-black. This high activity was ascribed to efficient charge transport from the electrode to the catalyst. The amount of O-2 evolved increased almost linearly with the amount of Ru-red for low loadings on Pt-black but decreased after passing an optimum loaded amount. This decrease was ascribed to bimolecular decomposition of the catalysts. The catalyst activity was analysed in terms of critical decomposition distance (r(d)/nm) by a surface adsorption model (SAM) and a void-space adsorption model (VAM); r(d) was estimated to be 1.37 nm for the SAM and 1.21 nm for the VAM.

DOI： 10.1039/ft9969203431

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A highly active electrocatalytic system to oxidise water to dioxygen (O-2) has been established using electrodeposited platinum black with an adsorbed trinuclear ruthenium complex (Ru-red). The catalyst turnover number for O-2 evolution was 1500 h(-1), four orders of magnitude greater than that of neat Pt-black. This high activity was ascribed to efficient charge transport from the electrode to the catalyst. The amount of O-2 evolved increased almost linearly with the amount of Ru-red for low loadings on Pt-black but decreased after passing an optimum loaded amount. This decrease was ascribed to bimolecular decomposition of the catalysts. The catalyst activity was analysed in terms of critical decomposition distance (r(d)/nm) by a surface adsorption model (SAM) and a void-space adsorption model (VAM); r(d) was estimated to be 1.37 nm for the SAM and 1.21 nm for the VAM.

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New potential-step chronoamperospectrometry (PSCAS) was employed to investigate the charge transport distance for Ru(bpy)(3)(2+) (bpy = 2,2'-bipyridine) complex dispersed in a Nafion(R) film coated on an ITO electrode by a mixture casting method. It was found that the charge transfer distance was independent of the concentration of the redox species in the polymer film at a given sample time under the PSCAS measurement if it is assumed that the distribution of the redox centers in the polymer follows Poisson statistics. Meanwhile, the sample time for the measurement was an important factor in determining the charge transfer distance between the redox molecules within the polymer film. The charge transfer distance increased with prolonged sample time, At the beginning of the PSCAS measurement at 1.3 V (SCE), the charge transport in the polymer film was ascribed to charge hopping. On a longer time scale, the slow increase of the charge transfer distance was ascribed to charge hopping involving bounded motion. From the different response time of the charge hopping and the bounded motion, the charge hopping distance between the adjacent redox complexes was estimated at 1.3 nm. The saturated charge transfer distance on a longer time scale was 1.6 nm, indicating that the bounded motion distance is about 0.3 nm. The estimated diffusion-limited charge hopping rate constant for the Ru(bpy)(3)(2+) complex in the Nafion(R) film was about 2.5 x 10(5) M(-1) s(-1) when the longest charge transfer distance was employed.

DOI： 10.1016/0022-0728(96)04592-5

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA LAUSANNE  

New potential-step chronoamperospectrometry (PSCAS) was employed to investigate the charge transport distance for Ru(bpy)(3)(2+) (bpy = 2,2'-bipyridine) complex dispersed in a Nafion(R) film coated on an ITO electrode by a mixture casting method. It was found that the charge transfer distance was independent of the concentration of the redox species in the polymer film at a given sample time under the PSCAS measurement if it is assumed that the distribution of the redox centers in the polymer follows Poisson statistics. Meanwhile, the sample time for the measurement was an important factor in determining the charge transfer distance between the redox molecules within the polymer film. The charge transfer distance increased with prolonged sample time, At the beginning of the PSCAS measurement at 1.3 V (SCE), the charge transport in the polymer film was ascribed to charge hopping. On a longer time scale, the slow increase of the charge transfer distance was ascribed to charge hopping involving bounded motion. From the different response time of the charge hopping and the bounded motion, the charge hopping distance between the adjacent redox complexes was estimated at 1.3 nm. The saturated charge transfer distance on a longer time scale was 1.6 nm, indicating that the bounded motion distance is about 0.3 nm. The estimated diffusion-limited charge hopping rate constant for the Ru(bpy)(3)(2+) complex in the Nafion(R) film was about 2.5 x 10(5) M(-1) s(-1) when the longest charge transfer distance was employed.

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The activity of a water oxidation catalyst based on a trinuclear Ru complex, Ruthenium Red (Ru-red) {[(NH3)(5)Ru-O-Ru(NH3)(4)-O-Ru(NH3)(5)](6+)} has been investigated both in a homogeneous aqueous solution (AS) and in a heterogeneous Nafion membrane (HM) using Ce-IV oxidant. In the AS, at higher concentrations, the oxygen (O-2) evolution rate V-o2 (mol s(-1)) decreases with increasing concentrations of Ru-red, but nitrogen (N-2) evolves. The N-2 evolution shows a bimolecular decomposition of the catalyst at high concentrations. In the HM, the V-o2 does not decrease even when the complex concentration in the membrane is ca. 30 times as high as the AS. A pseudo-first-order rate constant for oxidation of water by the catalyst (k(o2)/s(-1)) and a second-order rate constant for deactivation (k(deact)/dm(3) mol(-1) s(-1)) were obtained. The k(o2) values are close for both the AS and HM systems, indicating no significant loss of the activity in the membrane. The k(deact) value decreases by an order of two in the membrane, which is ascribed to the suppression of bimolecular decomposition of the catalyst. The apparent activity (k(app)/s(-1)) in the membrane increases upon decreasing the concentration of Ru-red due to suppression of the bimolecular decomposition. The effect of intermolecular distance distribution of the catalyst in the membrane on the catalytic activity has been analysed based on statistical calculations of the distribution. The critical decomposition distance between two adjacent complexes has been determined as 1.23 nm.

DOI： 10.1039/ft9969202457

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The activity of the electrochemical water oxidation catalyst based on Ru-red incorporated in an electrodecoated Nafion membrane was studied. The complex worked as an active catalyst, and an optimum concentration for the catalyst turnover number (TN) was exhibited. The TN increased with the concentration in low concentrations because of facilitated charge transfer between the catalysts, and the increase in the concentration brought about decreased TN due to bimolecular decomposition of the catalyst. An activity model for the electrochemical catalyst in a membrane was proposed based on intermolecular distance distribution, and the activity was analyzed in terms of a charge transfer distance (r(0)/nm) and a critical decomposition distance (r(d)/nm). Their values were obtained as 1.25 and 1.21 nm, respectively.

DOI： 10.1021/jp960402m

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：HUTHIG & WEPF VERLAG  

An ITO electrode was coated by a Nafion film incorporating Ru(bpy)(3)(2+) complex as redox centers either by mixture casting method, adsorption method, or swelling method and the electrochemical reactivity of the modified electrode was determined by the in-situ spectrocyclic voltammogram (SCV) in a sodium perchlorate aqueous solution at pa 1.2. A modified Poisson statistics equation was used to estimate the charge transfer distance (Re) between the Ru(bpy)(3)(2+) complexes. The estimated charge transfer distances for the electrodes prepared by swelling method (Ro = 1.63 nm for the electrode modified in M/W 1:10, and 1.69 nm in M/W 1:2) and adsorption method (Ro = 1.61 nm) were longer thant that for mixture casting method (Ro = 1.5 nm). Based on the different procedure of Ru(bpy)(3)(2+) complex incorporation in the Nafion film, the reasons that affect the apparent charge transfer distance were discussed.

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In an aqueous acid solution, the Ru(bpy)(3)(2+) photosensitized reduction of a macrocyclic Co-III complex, Co(N-4)(OH2)(2)(3+) (N-4 = 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-ditraazacyclotetradeca-4,11-diene), has been found to proceed in the presence of phenol. In Ru(bpy)(3)(2+)-Co(N-4)(OH2)(2)(3+)-phenol, the photosensitized reaction proceeds by electron transfer from the excited state Ru(bpy)(3)(2+) to the Co-III complex. Net charge separation is achieved owing to rapid reduction of the oxidized species of Ru(bpy)(3)(2+) by phenol molecules. The pH dependence of the charge-separation efficiency in the presence of phenol is quite different from that in the corresponding photosensitized system using teoa as a sacrificial donor. A partially reversible redox reaction such as slow reduction of the oxidized species of phenol and the oxidation of the Co-II generated takes place simultaneously with repetitive irradiations. The present results reveal that phenol is an excellent sacrificial donor, preferential to the usual ones such as teoa and EDTA for the photosensitized reaction in an aqueous acidic solution.

DOI： 10.1039/ft9969200969

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：HUTHIG & WEPF VERLAG  

An ITO electrode was coated by a Nafion film incorporating Ru(bpy)(3)(2+) complex as redox centers either by mixture casting method, adsorption method, or swelling method and the electrochemical reactivity of the modified electrode was determined by the in-situ spectrocyclic voltammogram (SCV) in a sodium perchlorate aqueous solution at pa 1.2. A modified Poisson statistics equation was used to estimate the charge transfer distance (Re) between the Ru(bpy)(3)(2+) complexes. The estimated charge transfer distances for the electrodes prepared by swelling method (Ro = 1.63 nm for the electrode modified in M/W 1:10, and 1.69 nm in M/W 1:2) and adsorption method (Ro = 1.61 nm) were longer thant that for mixture casting method (Ro = 1.5 nm). Based on the different procedure of Ru(bpy)(3)(2+) complex incorporation in the Nafion film, the reasons that affect the apparent charge transfer distance were discussed.

DOI： 10.1002/masy.19961050109

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

Trinuclear Ruthenium complex, Ru-red ([(NH3)(5)Ru-ORU(NH3)(4)-O-RU(NH3)(5)](6+)) is adsorbed well onto the electrodeposited Pt-black, and the adsorbed Ru-red works as a highly active catalyst for electrochemical water oxidation.

DOI： 10.1246/cl.1995.863

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA LAUSANNE  

Charge transfer between Ru(bpy):(2+)(3) (where bpy is 2,2'-bipyridine) complexes incorporated into a Nafion(R) membrane has been investigated using in situ spectrocyclic voltammetry and statistical calculation of the intermolecular distance between the complexes. The membrane was prepared either by a mixture casting method in which an alcoholic mixture solution of Nafion and the complex was cast to form a membrane, or by an adsorption method in which the complex was adsorbed from its aqueous solution into a precoated Nafion(R) membrane. It has been found that the electrochemical reactivity of the complex in a membrane prepared by the adsorption method is much higher than that prepared by the mixture casting method. The charge transfer distance between the complexes (R(0)) in the membrane prepared by the adsorption method was 1.6 nm (scan rate, 2 mV s(-1); pH 5.5), when assuming a random dispersion of the complex, which is significantly longer than that (1.1 nm) in the membrane prepared by the mixture casting method. The emission lifetime of the photoexcited Ru(bpy):(2+)(3) in the membrane suggests that the complex is localized in the membrane when it is prepared by an adsorption method; such localization would make the calculated R(0) value greater than the real value. The fraction of the volume in the membrane where the complex is adsorbed was estimated as 20 +/- 3%, by comparing the real local complex concentration in the membrane obtained from the R(0) value (1.1 nm) for the mixture casting system with the apparent average complex concentration.

DOI： 10.1016/0022-0728(95)03982-M

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Charge transport through a Nafion(R) membrane incorporating dispersed Ru(bpy)(3)(2+) (bpy = 2,2'-bipyridine) complex has been investigated by in-situ spectrocyclic voltammetry (SCV) measurements. The ratio R(CT) of the electrochemically active complexes was obtained from the visible absorption spectral change; it increased with increasing the complex concentration c in the membrane. The distribution of the intermolecular distance was taken into account using a statistical calculation. The relationship between R(CT) and c was derived on the basis of the center-to-center distance distribution between the nearest-neighbor molecules, and the value of the charge transfer distance R(0) was obtained from this relation using a charge-hopping model. The R(0) value depended on the scan rate of the potential. At high scan rates, at which bounded motion of the complex is almost negligible, R(0) = 0.93 nm was taken as the charge-hopping distance between adjacent redox centers. The R(0) value at slow scan rates (e.g. R(0) = 1.5 nm at 2 mV s(-1)) includes charge hopping between adjacent redox centers as well as the bounded motion of the complex.

DOI： 10.1016/0022-0728(94)03681-R

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The Ru(bpy)3(2+) photosensitized reduction of a macrocyclic Co(III) complex, Co(N4)(OH2)23+ (N4 = 5, 7, 7, 12, 14, 14-hexamethyl-1, 4, 8, 11-tetraazacyclotetradeca-4, 11-diene), has been investigated in the networks of gelatin hydrogel and hydrosol. In these systems, a net charge separation proceeds due to reduction of the Co(III) complex by the excited state of Ru(bpy)3(2+) and the scavenging of the oxidized species of Ru(bpy)3(2+) by a gelatin molecule. The photochemically generated Co(II) complex species reacts slowly with the oxidized species of gelatin. Then a reversible photo-induced redox reaction of Co(III) takes place repeatedly in these systems. The results indicate that the tyrosine residue in gelatin and the corresponding oxidized species in the oxidized form of gelatin act as a reducing agent for the oxidized form of the photosensitizer and an oxidizing agent for the reduced Co(III) species, respectively.

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Artificial photosynthesis is one of the promising clean-energy-providing systems of the future. Development of an efficient catalyst for water oxidation to evolve O-2 is indispensable for the construction of artificial photosynthetic devices. The photosynthetic oxygen evolving complex (OEC) composed of a tetranuclear manganese cluster serves as an excellent example of an efficient catalyst for water oxidation. Recently, significant progress has been reported in the development of manganese complexes as OEC models. The molecular aspects and activities of these manganese complexes toward water oxidation catalysis were reviewed in terms of homogeneous and heterogeneous catalysis systems. These could provide hints to design an efficient catalyst, as well as a key model reaction to understand the O-2 evolution mechanism in photosynthesis.

DOI： 10.1002/ejic.201300683

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Artificial photosynthesis is expected as one of promising clean energy-providing systems in future. Development of an efficient catalyst for water oxidation to evolve O<SUB>2</SUB> is a key task to yield a breakthrough for construction of an artificial photosynthetic device. Recently, significant progress has been reported in development of the molecular catalysts for water oxidation based on manganese, ruthenium and iridium complexes. The molecular aspects of the catalysts in chemical, electrochemical, and photo- or photoelectro-driven water oxidation were reviewed to provide hints to design an efficient catalyst. This review will mainly cover the related progress in the last 5 or 6 years.

DOI： 10.4019/bjscc.57.67

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DOI： 10.5796/electrochemistry.75.890

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DOI： 10.1295/kobunshi.52.333

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