Water reduction by a p-GaInP₂ photoelectrode stabilized by an amorphous TiO₂ coating and a molecular cobalt catalyst

Producing hydrogen through solar water splitting requires the coverage of large land areas. Abundant metal-based molecular catalysts offer scalability, but only if they match noble metal activities. We report on a highly active p-GaInP₂ photocathode protected through a 35-nm TiO₂ layer functionalized by a cobaloxime molecular catalyst (GaInP₂-TiO₂ -cobaloxime). This photoelectrode mediates H₂ production with a current density of ∼9 mA cm^-2 at a potential of 0 V versus RHE under 1-sun illumination at pH 13. The calculated turnover number for the catalyst during a 20-h period is 139,000, with an average turnover frequency of 1.9 s^-1. Bare GaInP₂ shows a rapid current decay, whereas the GaInP₂-TiO₂ -cobaloxime electrode shows ≤5% loss over 20 min, comparable to a GaInP₂-TiO₂-Pt catalyst particle-modified interface. The activity and corrosion resistance of the GaInP₂-TiO₂-cobaloxime photocathode in basic solution is made possible by an atomic layer-deposited TiO₂ and an attached cobaloxime catalyst.