Photoelectrochemical oxidation of anions by WO_3 in aqueous and nonaqueous electrolytes

Abstract

The behavior of WO_3 photoanodes has been investigated in contact with a combination of four anions (Cl−, CH_3SO_3−, HSO_4−, and ClO_4−) 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 WO_3. In 1.0 M aqueous strong acids, although the flat-band potential (E_(fb)) of WO_3 was dominated by electrochemical intercalation of protons into WO_3, 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 B_(10)Br_(10)^(˙−/2−) in acetonitrile, with a solution potential of 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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