A quantitative assessment of the competition between water and anion oxidation at WO3 photoanodes in acidic aqueous electrolytes

Abstract

The faradaic efficiency for O₂(g) evolution at thin-film WO₃ photoanodes has been evaluated in a series of acidic aqueous electrolytes. In 1.0 M H₂SO₄, persulfate was the predominant photoelectrochemical oxidation product, and no O₂ was detected unless catalytic quantities of Ag⁺(aq) were added to the electrolyte. In contact with 1.0 M HClO₄, dissolved O₂ was observed with nearly unity faradaic efficiency, but addition of a hole scavenger, 4-cyanopyridine N-oxide, completely suppressed O₂ formation. In 1.0 M HCl, Cl₂(g) was the primary oxidation product. These results indicate that at WO₃ photoanodes, water oxidation is dominated by oxidation of the acid anions in 1.0 M HCl, H₂SO₄, and HClO₄, respectively.