A Ru(II)-Re(I) supramolecular photocatalyst and a Ru(II) redox photosensitizer were both deposited successfully on a NiO electrode by using methyl phosphonic acid anchoring groups and the electrochemical polymerization of the ligand vinyl groups of the complexes. This new molecular photocathode, poly-RuRe/NiO, adsorbed a larger amount of the metal complexes compared to one using only methyl phosphonic acid anchor groups, and the stability of the complexes on the NiO electrode were much improved. The poly-RuRe/NiO acted as a photocathode for the photocatalytic reduction of CO at E = -0.7 V vs Ag/AgCl under visible-light irradiation in an aqueous solution. The poly-RuRe/NiO produced approximately 2.5 times more CO, and its total Faradaic efficiency of the reduction products improved from 57 to 85%.

Mixed-anion compounds (e.g., oxynitrides and oxysulfides) are potential candidates as photoanodes for visible-light water oxidation, but most of them suffer from oxidative degradation by photogenerated holes, leading to low stability. Here we show an exceptional example of a stable, mixed-anion water-oxidation photoanode that consists of an oxyfluoride, Pb 2 Ti 2 O 5.4 F 1.2 , having a band gap of ca. 2.4 eV. Pb 2 Ti 2 O 5.4 F 1.2 particles, which were coated on a transparent conductive glass (FTO) support and were subject to postdeposition of a TiO 2 overlayer, generated an anodic photocurrent upon band gap photoexcitation of Pb 2 Ti 2 O 5.4 F 1.2 (λ <520 nm) with a rather negative photocurrent onset potential of ca. −0.6 V vs NHE, which was independent of the pH of the electrolyte solution. Stable photoanodic current was observed even without loading a water oxidation promoter such as CoO x . Nevertheless, loading CoO x onto the TiO 2 /Pb 2 Ti 2 O 5.4 F 1.2 /FTO electrode further improved the anodic photoresponse by a factor of 2−3. Under AM1.5G simulated sunlight (100 mW cm −2 ), stable water oxidation to form O 2 was achieved using the optimized Pb 2 Ti 2 O 5.4 F 1.2 photoanode in the presence of an applied potential smaller than 1.23 V, giving a Faradaic efficiency of 93% and almost no sign of deactivation during 4 h of operation. This study presents the first example of photoelectrochemical water splitting driven by visible-light excitation of an oxyfluoride that stably works, even without a water oxidation promoter, which is distinct from ordinary mixed-anion photoanodes that usually require a water oxidation promoter.

A durable molecular photocathode driving CO2 reduction with over 1200 of turnover number was developed by electropolymerization of Ru(ii) complexes. The cell with a suitable photoanode enabled CO2 reduction with H2O oxidation with no bias for 24 h.

Non‐oxide materials such as oxynitrides are good candidates as photoanodes for visible‐light‐driven water oxidation, but most of them suffer from oxidative degradation by photogenerated holes, resulting in low stability. Herein we developed a photoanode using a visible‐light‐responsive TiO2 powder doped with tantalum and nitrogen (TiO2:Ta/N) for water oxidation. The Ta/N codoping enabled a stable anodic photocurrent response attributable to water oxidation under visible‐light irradiation. Surface modification of the TiO2:Ta/N anode with RuOx species further facilitated water oxidation catalysis, achieving stable O2 evolution over 5 h of operation with no sign of deactivation. Operando XAFS measurements revealed an important function of the RuOx species as a collector of photogenerated holes in TiO2:Ta/N, facilitating the photoelectrochemical water oxidation. Visible‐light‐driven H2 evolution and solar‐driven CO2 reduction into CO were both achieved by using water as an electron donor in photoelectrochemical cells with the TiO2:Ta/N photoanode coupled to a Pt cathode and a Ru(II)–Re(I) binuclear complex photocathode, respectively.

The development of systems for photocatalytic CO2 reduction with water as a reductant and solar light as an energy source is one of the most important milestones on the way...