Improving the stability and selectivity for the oxygen-evolution reaction on semiconducting WO3 photoelectrodes with a solid-state FeOOH catalyst

Abstract

WO₃ electrodes were synthesized via a sol–gel route followed by the photoelectrochemical deposition of a solid state FeOOH oxygen-evolution catalyst (OEC) to observe its effects on electrode stability and selectivity towards the oxygen evolution reaction (OER). WO₃ photoanodes have been reported to degrade in aqueous solutions with pH > 3 due to the material's Arrhenius acidity and the potential formation of reactive peroxide intermediates on the WO₃ surface during the course of photoelectrochemical water oxidation. The stability during photoelectrochemical OER of WO₃ and WO₃–FeOOH photoanodes was measured at 1.23 V vs. RHE at pH 4 and 7 in phosphate-buffered solutions. Additionally, the faradaic efficiencies of the electrodes for OER were measured at pH 4. WO₃–FeOOH electrodes demonstrate a 95.9 ± 1.6% faradaic efficiency for OER in pH 4 potassium phosphate buffer at current densities of ∼0.75 mA cm⁻² under 200 mW cm⁻² AM1.5G illumination and an applied bias of 1.43 V vs. RHE. These experiments demonstrate that adding an FeOOH co-catalyst dramatically improves the stability of the electrodes, selectivity, and rate of OER versus that observed on WO₃ films.