WO₃-α-Fe₂O₃ composite photoelectrodes with low onset potential for solar water oxidation

The physical and photoelectrochemical properties of a composite oxide photoelectrode comprised of α-Fe₂O₃ and WO ₃ crystals is investigated. The composite films exhibit a water oxidation photocurrent onset potential as low as 0.43 V vs. RHE, a value considerably lower than that of pure α-Fe₂O₃ photoanodes prepared in comparable synthesis conditions. This result represents one of the lowest onset potentials measured for hematite-based PEC water oxidation systems. Compositional analysis by X-ray Photoelectron Spectroscopy and Energy Dispersive Spectroscopy indicates the composition of the films differs between the surfaces and bulk, with tungsten found to be concentrated in the surface region. Post-reaction Raman spectroscopy characterization demonstrates that water interacts with surface WO₃ crystals, an event that is associated with the formation of a hydrated form of the oxide.