Visible-light-driven nonsacrificial water oxidation over tungsten trioxide powder modified with two different cocatalysts

Tungsten trioxide (WO₃) powder was studied as a photocatalyst for water oxidation under visible light (λ > 420 nm). WO₃ modified with nanoparticulate Pt species (more specifically, PtO_x) as cocatalysts is capable of photocatalyzing water oxidation under visible light in the presence of iodate (IO₃^-) ions as an electron acceptor under near-neutral pH conditions (pH ≈ 5.9). When PtO _x/WO₃ was further modified with a very small amount (0.001 wt%) of a metal oxide (e.g., MnO_x, CoO_x, RuO₂ or IrO₂) as a secondary cocatalyst, the water oxidation activity was improved. Among the metal oxide cocatalysts examined, RuO₂ was found to give the highest performance, with an apparent quantum yield of 14.4% at 420 nm. The results of photocatalytic reactions and photoelectrochemical analyses suggest that the main roles of the loaded PtO_x and RuO₂ on WO₃ are to promote the reduction of IO₃^- and water oxidation, respectively.