Experimental Evidence for Photoactivated BiVO4 Anodes with Enhanced Photoelectrochemical Water Oxidation

Photoactivated bismuth vanadate (BiVO4) anodes are highly promising candidates for solar-driven water splitting. Extant research has shown that prolonged light exposure results in the formation of a borate cocatalyst junction layer on the BiVO4 anode surface, which is attributable to the photocorrosion of BiVO4 and etching modification in a borate electrolyte; consequently, the photocurrent is significantly increased. This study analyzes the effects of light alone on photoactivated BiVO4 anodes in the absence of the borate cocatalyst. We utilized photocorrosion- and etching-resistant BiVO4 to prevent formation of the borate cocatalyst overlayer and investigated the effects of short-duration light irradiation on the photoelectrochemical (PEC) properties. Remarkably, we observed that pretreatment with a mere 20 min of light exposure in both air and electrolyte resulted in a notable increase in the photocurrent. In addition, this photoactivation effect recurred via repeated light irradiation and dark storage. The PEC technique was used to show that the intraband gap states reduced after photoactivation, and hole accumulation increased on the photoactivated BiVO4 surface during the subsequent water oxidation reaction. Furthermore, the spectroelectrochemical spectra revealed that the hole-trapping absorbance of photoactivated BiVO4 decreased. Photoincident absorption spectroscopy and transient absorption spectroscopy further showed an increased population of the photogenerated holes and an extended lifetime on the microsecond time scale, respectively, which contributed to improved PEC water-splitting activity with the photoactivated BiVO4. These findings are expected to offer deeper insights into the trap-filling mechanism underlying BiVO4 photoactivation and its effect on PEC water splitting.