Ir-phosphate cocatalyst for photoelectrochemical water oxidation using α-Fe2O3

Abstract

α-Fe₂O₃ is an ideal photoanode for solar water oxidation owing to its visible light absorbing capability, suitable valence band position, low cost, high abundance, non-toxicity and eco-friendliness. However, the reported efficiencies are very low due to the poor kinetics of water oxidation by photogenerated holes on α-Fe₂O₃. In the present study, an α-Fe₂O₃ electrode is obtained by heating a film of Fe which is prepared by the electrochemical reduction of Fe²⁺ ions. Film thickness and calcination temperature are carefully optimized to get a maximum photoresponse in neutral phosphate solution. In order to improve the water oxidation kinetics and reduce the charge carrier recombination, an iridium-phosphate (Ir-Pi) catalyst is electrodeposited on the surface of α-Fe₂O₃. Ir-Pi is found to reduce the OER onset potential by 350 mV, and enhances the photocurrent density by 3 times at 1.23 V vs. RHE.