Improving BiVO4 photoanodes for solar water splitting through surface passivation

Abstract

BiVO₄ has shown great potential as a semiconductor photoanode for solar water splitting. Significant improvements made during recent years allowed researchers to obtain a photocurrent density of up to 4.0 mA cm⁻² (AM1.5 sunlight illumination, 1.23 V_RHE bias). For further improvements of the BiVO₄ photoelectrodes, a deep understanding of the processes occurring at the BiVO₄–H₂O interface is crucial. Employing an electrochemical loading and removal process of NiO_x, we show here that carrier recombination at this interface strongly affects the photocurrents. The removal of NiO_x species by electrochemical treatment in a phosphate electrolyte leads to significantly increased photocurrents for BiVO₄ photoelectrodes. At a bias of 1.23 V_RHE, the Incident Photon-to-Current Efficiency (IPCE) at 450 nm reaches 43% for the passivated BiVO₄ electrode under back side illumination. A model incorporating heterogeneity of NiO_x centers on the BiVO₄ surface (OER catalytic centers, recombination centers, and passivation centers) is proposed to explain this improved performance.