Photoelectrochemical oxidation of anions by WO3 in aqueous and nonaqueous electrolytes

By Mi, Qixi; Coridan, Robert H.; Brunschwig, Bruce S.; Gray, Harry B. & Lewis, Nathan S.
Published in Energy Environ. Sci. The Royal Society of Chemistry 2013

Abstract

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[radical dot]-/2- in acetonitrile, with a solution potential of [similar]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.

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