Photocorrosion of WO 3 Photoanodes in Different Electrolytes.

Photocorrosion of an n-type semiconductor is anticipated to be unfavorable if its decomposition potential is situated below its valence band-edge position. Tungsten trioxide (WO 3 ) is generally considered as a stable photoanode for different photoelectrochemical (PEC) applications. Such oversimplified considerations ignore reactions with electrolytes added to the solvent. Moreover, kinetic effects are neglected. The fallacy of such approaches has been demonstrated in our previous study dealing with WO 3 instability in H 2 SO 4 . In this work, in order to understand parameters influencing WO 3 photocorrosion and to identify more suitable reaction environments, H 2 SO 4 , HClO 4 , HNO 3 , CH 3 O 3 SH, as electrolytes are considered. Model WO 3 thin films are fabricated with a spray-coating process. Photoactivity of the samples is determined with a photoelectrochemical scanning flow cell. Photostability is measured in real time by coupling an inductively coupled plasma mass spectrometer to the scanning flow cell to determine the photoanode dissolution products. It is found that the photoactivity of the WO 3 films increases as HNO 3 < HClO 4 ≈ H 2 SO 4 < CH 3 O 3 SH, whereas the photostability exhibits the opposite trend. The differences observed in photocorrosion are explained considering stability of the electrolytes toward decomposition. This work demonstrates that electrolytes and their reactive intermediates clearly influence the photostability of photoelectrodes. Thus, the careful selection of the photoelectrode/electrolyte combination is of crucial importance in the design of a stable photoelectrochemical water-splitting device.