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Geometric isomers of mononuclear ruthenium(II) complexes

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.

Facile and scalable fabrication of α-Fe2O3 photoanodes using a precursor solution containing FeIII ions and 1-ethylimidazole (EIm) in methanol was demonstrated to afford a rigidly adhered α-Fe2O3 film with a controllable thickness on a fluorine-doped tin oxide (FTO) substrate. EIm ligation to FeIII ions in the precursor solution brought about high crystallinity of three-dimensionally well-interconnected nanoparticles of α-Fe2O3 upon sintering. This is responsible for the 13.6 times higher photocurrent density (at 1.23 V vs reference hydrogen electrode (RHE)) for photoelectrochemical (PEC) water oxidation on the α-Fe2O3 (w-α-Fe2O3) photoanode prepared with EIm compared with that (w/o-α-Fe2O3) prepared without EIm. The w-α-Fe2O3 photoanode provided the highest charge separation efficiency (ηsep) value of 27% among the state-of-the-art pristine α-Fe2O3 photoanodes, providing incident photon-to-current conversion efficiency (IPCE) of 13% at 420 nm and 1.23 V vs RHE. The superior ηsep for the w-α-Fe2O3 photoanode is attributed to the decreased recombination of the photogenerated charge carriers at the grain boundary between nanoparticles, in addition to the higher number of the catalytically active sites and the efficient bulk charge transport in the film, compared with w/o-α-Fe2O3.

Electrocatalytic splitting of water to oxygen and hydrogen is one of the most promising approaches for sustainable production of hydrogen as a carbon-neutral fuel. To establish efficient electrocatalytic water splitting, the overall overpotential for this reaction must be minimized via developing efficient catalysts to promote oxygen and hydrogen evolution at the anode and the cathode, respectively. However, the overpotentials for oxygen evolution are insufficiently low (162–300 mV for a current density of 10 mA cm−2), and the value less than 100 mV still remains untracked. Here, we report the unprecedentedly low of 32 mV for oxygen evolution attained by the formation of a unique motif of nickel sulfide nanowires stuffed into carbon nitride scabbards (NiSx/C3N4), demonstrating electrocatalytic water splitting at the lowest overall overpotential of 72 mV using the NiSx/C3N4 anode. This motif provides a key to guided thought for the development of efficient catalysts for oxygen evolution.

Oxygen-evolution-reaction (OER) and oxygen-reduction-reaction (ORR) catalysts on a gas-diffusion carbon paper (CP) electrode have been explored as a current hot topic. Low-cost and earth-abundant F...

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.

A ruthenium complex showing multi-stimuli-responsive isomerization was synthesized. The catalytic activity of this complex toward water oxidation showed responses to visible-light irradiation and heat due to photoisomerization and thermal back-isomerization, respectively. DFT calculations suggested that a pendant moiety in the complex was key to controlling the catalytic activity.

Nanorod architecture of a N2-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 so...

The development of efficient catalyst materials for water oxidation is bottleneck to construct artificial photosynthesis that is a promising future energy-providing system. We review the recent progress on development of IrOx electrocatalyst films for water oxidation based on our latest research works. A controlled fabrication approach of an efficient IrOx electrocatalyst films is introduced by a facile spin-coating of a homogenous solution of Ir precursor complexes followed by simple annealing at different temperature. The composition and crystallinity of the IrOx film are tunable by a simple annealing treatment. The electrocatalytic properties of the IrOx film dramatically depended on annealing temperature are characterized to give the noticeably high performance at 300 °C annealing. A soft-template-assisted technique using different polymer surfactants as structure directing agents (SDAs) is illustrated in the spin-coating procedure to reveal impacts of SDAs on nanostructures and electrocatalytic water oxidation performances of the IrOx films. The characterization of the first accessible channel-like open pore architecture of the ordered 2D-hexagonal mesoporous IrOx film is described by a facile one-pot strategy using Pluronic F127 as SDA. The novel controlled nanostructures including mesoporous architecture of IrOx improves electrocatalytic performance for water oxidation relative to a conventional nanoparticulate structure of IrOx coating.

Post-fermented tea (dark tea) is produced from enzyme-inactivated fresh tea leaves by microbial fermentation. Batabata tea and Awaban tea are two major dark teas fermented under aerobic and anaerobic conditions, respectively. However, how their chemical compositions and functionalities change during different post-fermentation processes remains unclear. Nuclear magnetic resonance (NMR)-based analyses showed that (-)-epigallocatechin gallate (EGCG), (-)-epigallocatechin (EGC) and (-)-epicatechin (EC) decreased in Batabata tea during post-fermentation with aerobic molds. In contrast, EGC and EC increased, and pyrogallol was produced in Awaban tea during post-fermentation with lactic acid bacteria (LAB). The anti-glycation activities of two dark teas were investigated using an in vitro assay system with human serum albumin (HSA). The anti-glycation activity decreased in Batabata tea, but it was retained in Awaban tea during post-fermentation. Our results showed that post-fermentation with LAB was an efficient way to enhance phenol content and that pyrogallol contributed to anti-glycation activity of Awaban tea.

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 K 2 SO 4 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 Na 2 B 4 O 7 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 K 2 SO 4 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.

The passage number of cells refers to the number of subculturing processes that the cells have undergone. The effect of passage number on morphological and phenotypical characteristics of cells is of great importance. Advanced glycation end products have also been associated with cell functionality and characteristics. Murine monocyte RAW 264.7 cells differentiate into osteoclasts upon receptor activation caused by nuclear factor-kappa-Β ligand (RANKL) treatment. This study aims to identify the role of passage number on intracellular advanced glycation end products (AGEs) formation and osteoclastogenic differentiation of RAW 264.7 cells. Western blotting was performed to check intracellular AGE formation along with fluorometric analysis using a microplate reader. Tartrate-resistant acid phosphatase (TRAP) staining was performed to check osteoclastogenic differentiation, and qPCR was realized to check the responsible mRNA expression. Immunofluorescence was used to check the morphological changes. Intracellular AGE formation was increased with passaging, and the higher passage number inhibited multinucleated osteoclastogenic differentiation. Osteoclastogenic gene expression also showed a reducing trend in higher passages, along with a significant reduction in F-actin ring size and number. Lower passages should be used to avoid the effects of cell subculturing in in vitro osteoclastogenesis study using RAW 264.7 cells.

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.

proximal,proximal-(p,p)-[RuII2(tpy)2LXY]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 RuII(μ-OH)RuII 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-[Ru2(tpy)2L(μ-Cl)]3+ (Ru2(μ-Cl)), p,p-[Ru2(tpy)2L(μ-OH)]3+ (Ru2(μ-OH)), p,p-[Ru2(tpy)2L(OH)(OH2)]3+ (Ru2(OH)(OH2)), and p,p-[Ru2(tpy)2L(OH)2]2+ (Ru2(OH)2) in aqueous solution. Ru2(μ-Cl) converted slowly (10–4 s–1) to Ru2(μ-OH), and further Ru2(μ-OH) converted very slowly (10–6 s–1) to Ru2(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, Ru2(OH)(OH2) was predicted to be thermodynamically stable by 13.3 kJ mol–1 in water compared to Ru2(μ-OH) because of the specially stabilized core structure by multiple hydrog...

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. ≤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 EO-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 IrOx 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.

A novel type of trimethylanilinium-substituted pyrene derivative, 1,6-di(N,N,N-trimethylanilinium-4-yl)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 (Φf), and lifetime (τ) 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.

Pigmentation in the dermis is known to be caused by melanophages, defined as melanosome-laden macrophages. In this study, we show that dermal fibroblasts also have an ability to uptake melanosomes and apoptotic melanocytes. We have previously demonstrated that normal human melanocytes constantly secrete melanosome clusters from various sites of their dendrites. After adding secreted melanosome clusters collected from the culture medium of melanocytes, time-lapse imaging showed that fibroblasts actively attached to the secreted melanosome clusters and incorporated them. Annexin V staining revealed that phosphatidylserine (PtdSer), which is known as an &lsquo, eat-me&rsquo, signal that triggers the internalization of apoptotic cells by macrophages, is exposed on the surface of secreted melanosome clusters. Dermal fibroblasts were able to uptake secreted melanosome clusters as did macrophages, and those fibroblasts express TIM4, a receptor for PtdSer-mediated endocytosis. Further, co-cultures of fibroblasts and melanocytes demonstrated that dermal fibroblasts internalize PtdSer-exposed apoptotic melanocytes. These results suggest that not only macrophages, but also dermal fibroblasts contribute to the collection of potentially toxic substances in the dermis, such as secreted melanosome clusters and apoptotic melanocytes, that have been occasionally observed to drop down into the dermis from the epidermis.

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 (∼2 μm 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 λmax (the extinction band maximum) = 683 nm. The spectral shapes and λmax 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.

distal-[Ru(Cl-tpy)(pynp)Cl]+ (d-2Cl) (Cl-tpy = 4′-chloro-2,2′;6′,2″-terpyridine, pynp = 2-(2-pyridyl)-1,8-naphthyridine), and distal- and proximal-[Ru(Cl-tpy)(pynp)OH2]2+ (d- and p-2H2O) 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-1H2O). The equilibrium turned out to be involved in the aquation reaction of d-2Cl to d-2H2O 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-2H2O to p-2H2O occurs by visible light irradiation as it is for d-1H2O, and Φ (2.1%) at 520 nm for photoisomerization of d-2H2O was higher than that (1.5%) observed for d-1H2O. d-2H2O undergoes the two-step reaction involving the successive one-proton-coupled one-electron reactions of the RuII OH2/RuIII OH and RuIII OH/RuIV O redox couples, whereas p-2H2O undergoes the one-step reaction involving the two-proton-coupled two-electron reaction of the RuII OH2/RuIV O redox couple. These redox potentials of d- and p-2H2O are higher than those for d- and p-1H2O at pH 7.0 by 10 ∼ 50 mV due to the electron-withdrawing chloro substitution. The turnover frequency ( k O 2 = 6.3 × 10 − 3 s − 1 ) of d-2H2O for water oxidation was higher than that (3.9 × 10−4 s−1) of p-2H2O by a factor of 16. kO2 for d-2H2O was also 1.6 times higher than that (3.8 × 10−3 s−1) for d-1H2O, whereas kO2 for p-2H2O was 1.2 times lower than that (4.8 × 10−4 s−1) for p-1H2O.

Electrochemical water oxidation by [Ru(EtOtpy)(bpy)OH 2 ] 2+ ( 1 ) (EtOtpy = 4′-ethoxy-2,2′:6#6°6#′-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 OH 2 / 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 1 (Ru II OH 2 ) 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 1.52 V to 0.22 V vs SCE exhibited that Ru II OH 2 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.

The quasi-stable excited states of distal - and proximal -[Ru(tpy)(pynp)OH 2 ] 2+ (tpy = 2,2′,6′,2″-terpyridine, pynp = 2-(2-pyridyl)-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 ( 3 MLCT) 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 OH 2 ligands in the proximal -isomer. The strong interaction between the low lying 3 MLCT 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 ( 3 MC) state from the high-lying 3 MLCT state in the case of the distal -isomer.

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-μ-oxo dinuclear manganese complex, [(OH2)(terpy)Mn(III)(μ-O)2Mn(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)(μ-O)2Mn(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 (1ads) adsorbed on mica for KMnO4- and Oxone-treated systems, indicating that 1' (1'ads) and 2 (2ads) adsorbed on mica do not work for the catalysis. The kinetic analysis suggested that 1ads works for the catalysis through cooperation with adjacent 1ads or 2ads, meaning that 2ads assists the cooperative catalysis by 1ads though 2ads is not able to work for the catalysis alone. For the Ce(IV)-treated system, O2 evolution was hardly observed although the sufficient amount of 1ads 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 Ce(3+) cations (generated in oxidative dimerization of 1') co-adsorbed with 1ads.

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 1H 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 (9.2 × 10–2 s–1 at 40 μM) of p-RuCl to form p-RuH2O is 1700 times higher than that (5.4 × 10–5 s–1 at 63 μM) 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 = 1.7 × 10–3 s–1) of p-RuH2O for catalytic water oxidation is 1.7 times greater than that (1.0 × 10–3 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.

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 film from the parent metal. The electrochemical reaction is driven by only a 1 V bias with respect to a Pt counter electrode in an aqueous solution. The solution contained an inexpensive, less toxic potassium hydroxide, and the reaction produced favorable byproducts, namely, recyclable K8Nb6O19 and H2.

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 (λ > 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.

The influencing factors on heterogeneous water oxidation catalysis (WOC) were investigated in a synthetic photosystem II model developed by adsorbing [(OH2)(terpy)MnIII(μ-O)2MnIV(terpy)(OH2)]3+ (terpy = 2,2′:6′,2″-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 °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 °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.