Photoelectrochemical Behavior of WO₃ in an Aqueous Methanesulfonic Acid Electrolyte

N-type semiconducting WO₃ is widely investigated as a photoanode operating in water and seawater splitting devices. Because of the propensity of WO₃ to favor photo-oxidation of acidic electrolyte anions and, in parallel, the formation on the electrode surface of the peroxo species, the choice of the appropriate electrolyte to allow stable operation of the photoanode is of critical importance. Our results from structural and photoelectrochemical tests performed using mesoporous WO₃ photoanodes exposed to 80 h long photoelectrolysis in a 1 M aq. methanesulfonic acid supporting electrolyte demonstrate the photostability of both the WO₃ photomaterial and the CH₃SO₃H electrolyte. The reasons for the stability of aqueous solutions of CH₃SO₃H are discussed on the basis of earlier literature reports.