C3ee40712h 2646..2653

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 (Efb) of WO3 was dominated by electrochemical intercalation of protons into WO3, the nature of the electrolyte influenced the onset potential (Eon) of the anodic photocurrent. In aprotic solvents, the electrolyte anion shifted both Efb and Eon, 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 1.7 V vs. the normal hydrogen electrode, exhibited an opencircuit photovoltage of 1.32 V under 100 mW cm 2 of simulated Air Mass 1.5 global illumination.