An In-Air Illumination Induced Surface Transformation for Mitigating Charge Recombination at BiVO4 Photoanodes.

Illumination treatment is frequently employed to modify the surface and/or bulk properties of photoelectrodes. This strategy has been demonstrated to be particularly effective in improving the photoelectrochemical performance of bismuth vanadate (BiVO4), a promising photoanode material. However, the mechanistic role of this treatment remains elusive. Here we show that in-air illumination induces surface transformation in BiVO4 photoanodes, doubling the photocurrent for water oxidation. Through spectroscopic and photoelectrochemical techniques, we find that the illumination process suppresses surface-state-mediated charge recombination and is accompanied by the formation of oxygen-vacancy-related paramagnetic centers and increased surface hydroxylation. The increased surface hydroxylation is associated with longer-lived surface holes and accelerated oxygen-evolution kinetics, leading to overall performance gains. These findings offer new insight into the longstanding ambiguities surrounding the effects of illumination treatment on tailoring surface charge dynamics and enhancing light conversion efficiency of BiVO4 photoanodes.