A bifunctional lead–iron oxyfluoride, PbFeO2F, that functions as a visible-light-responsive photoanode and an electrocatalyst for water oxidation

Abstract

The oxyfluoride PbFeO₂F was investigated as a photoanode material and as an electrocatalyst for water oxidation. PbFeO₂F powder, which was synthesized by a high-pressure method and had an estimated bandgap of 2.1 eV, was deposited onto a fluorine-doped tin oxide (FTO) substrate. Mott–Schottky plot measurements for the PbFeO₂F/FTO electrode showed n-type semiconductivity of PbFeO₂F, with a flat-band potential of +0.53 ± 0.05 V vs. reversible hydrogen electrode (RHE). The PbFeO₂F/FTO electrode, which was modified with a conductive TiO₂ layer and a cobalt phosphate water-oxidation cocatalyst, showed a clear anodic photocurrent in aqueous K₃PO₄ solution under visible-light irradiation (λ < 600 nm). The PbFeO₂F/FTO electrode without any modification functioned as a stable water-oxidation electrocatalyst to form O₂ with a faradaic efficiency of close to unity. This study demonstrates that PbFeO₂F is a bifunctional material, serving as a water-oxidation photoanode under a wide range of visible-light wavelengths and as an electrocatalyst that operates at a relatively low overpotential for water oxidation.