Photoelectrochemical oxidation of anions by WO3 in aqueous and nonaqueous electrolytes

The behavior of WO3 photoanodes has been investigated in contact with a combination of four anions Cl-, CH3SO3-, HSO4-, and ClO4-) and three solvents (water, acetonitrile, and propylene carbonate), to elucidate the role of the semiconductor surface, the electrolyte, and redox kinetics on the current density vs. potential properties of n-type WO3. In 1.0 M aqueous strong acids, although the flat-band potential (E-fb) of WO3 was dominated by electrochemical intercalation of protons into WO3, the nature of the electrolyte influenced the onset potential (E-on) of the anodic photocurrent. In aprotic solvents, the electrolyte anion shifted both E-fb and E-on, but did not significantly alter the overall profile of the voltammetric data. For 0.50 M tetra(n-butyl) ammonium perchlorate in propylene carbonate, the internal quantum yield exceeded unity at excitation wavelengths of 300-390 nm, indicative of current doubling. A regenerative photoelectrochemical cell based on the reversible redox couple B10Br10-/2- in acetonitrile, with a solution potential of similar to 1.7 V vs. the normal hydrogen electrode, exhibited an open-circuit photovoltage of 1.32 V under 100 mW cm(-2) of simulated Air Mass 1.5 global illumination.