Earth-Abundant Molecular Z-Scheme Photoelectrochemical Cell for Overall Water-Splitting

A push-pull organic dye and a cobaloxime catalyst were successfully cografted on NiO and CuGaO₂ to form efficient molecular photocathodes for H₂ production with >80% Faradaic efficiency. CuGaO₂ is emerging as a more effective p-type semiconductor in photoelectrochemical cells and yields a photocathode with 4-fold higher photocurrent densities and 400 mV more positive onset photocurrent potential compared to the one based on NiO. Such an optimized CuGaO₂ photocathode was combined with a TaON|CoO _x photoanode in a photoelectrochemical cell. Operated in this Z-scheme configuration, the two photoelectrodes produced H₂ and O₂ from water with 87% and 88% Faradaic efficiency, respectively, at pH 7 under visible light and in the absence of an applied bias, equating to a solar to hydrogen conversion efficiency of 5.4 × 10^-3%. This is, to the best of our knowledge, the highest efficiency reported so far for a molecular-based noble metal-free water splitting Z-scheme.