Solar Water Oxidation by a Visible-Light-Responsive Tantalum/Nitrogen-Codoped Rutile Titania Anode for Photoelectrochemical Water Splitting and Carbon Dioxide Fixation

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 O-2 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 H-2 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.