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

Bismuth vanadate (BiVO4) have 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 BiVO4 electrodes. A 54% improvement on the photocurrent density was obtained using the Al- modified BiVO4 electrode, accompanied by a 15% increase in stability over 7.5 hours 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 BiVO4 powders. This study presents useful, previously unreported information about the surface chemistry of BiVO4 based on experimental methods and gives unique insights on the characterization of the BiVO4 surface. The existence of surface reactive sites on BiVO4 was confirmed and quantified (1.5 reactive sites/nm2) via chemical titration.