Insights on the surface chemistry of BiVO4 photoelectrodes and the role of Al overlayers on its water oxidation activity

Bismuth vanadate (BiVO4) has surface states that give rise to defect levels that mediate electron-hole recombination. In order to minimize the inefficiencies, an ultrathin Al overlayer was deposited on the BiVO4electrodes. A 54 % improvement on the photocurrent density was obtained using the Al-modified BiVO4electrode, accompanied by a 15 % increase in stability over 7.5 h of continuous irradiation. Moreover, surface capacitance measurements showed that the Al overlayer was indeed passivating the surface states. We also shed light on the deposition of an Al overlayer on the surface of BiVO4, by investigating the process on model BiVO4powders. This study presents useful, previously unreported information about the surface chemistry of BiVO4based on experimental methods and gives unique insights on the characterization of the BiVO4surface. The existence of surface reactive sites on BiVO4was confirmed and quantified (1.5 reactive sites/nm2) via chemical titration