(Invited) Role of Surface States in Photocatalytic Oxygen Evolution with CuWO 4  Particles

CuWO 4 is a medium bandgap (2.3 eV) n-type semiconductor capable of photoelectrochemical water oxidation under applied electrical bias. Here, we show for the first time that suspended microcrystals CuWO 4 evolve oxygen photocatalytically under visible illumination from solutions of 0.05 M AgNO 3 (10.8 μmol/hour; AQE of 0.561% at 400 nm) and 0.0002 M FeCl 3 (1.5 μmol/hour). No oxygen is detected with 0.002 M [Fe(CN) 6 ] 3- as sacrificial agent. The activity dependence on the redox potential of the acceptors is due to the presence of Cu 2+ based electron trap states in CuWO 4 . According to surface photovoltage spectroscopy and electrochemistry, these states are located on the particle surface, 1.8 eV above the valence band edge of the material. Controlling the chemistry of these states will be key to uses of CuWO 4 particles in tandem catalysts for overall water splitting. Figure 1