Recent progress of visible-light-driven heterogeneous photocatalysts for overall water splitting

TaON and MTaO2N (M: Ca, Sr, Ba), Ta5+-based (oxy)nitrides, were studied as visible-light-driven photocatalysts. Under visible light irradiation (λ≥420 nm), TaON oxidized water to O2 and reduced H+ to H2 in the presence of sacrificial reagents (Ag+ and methanol). TaON efficiently oxidized water into O2, with a maximum quantum yield of 34%. H2 evolution on TaON photocatalyst was found to be remarkably enhanced by adding Ru as a noble-metal cocatalyst. In contrast, MTaO2N did not oxidize water under photocatalytic reaction condition although the oxynitride evolved H2 in the presence of methanol under visible light irradiation.