Photoelectrochemical Behavior of WO 3 in an Aqueous Methanesulfonic Acid Electrolyte.

N-type semiconducting WO 3 is widely investigated as a photoanode operating in water and seawater splitting devices. Because of the propensity of WO 3 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 WO 3 photoanodes exposed to 80 h long photoelectrolysis in a 1 M aq. methanesulfonic acid supporting electrolyte demonstrate the photostability of both the WO 3 photomaterial and the CH 3 SO 3 H electrolyte. The reasons for the stability of aqueous solutions of CH 3 SO 3 H are discussed on the basis of earlier literature reports.