BiVO 4 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 À2 (AM1.5 sunlight illumination, 1.23 V RHE bias). For further improvements of the BiVO 4 photoelectrodes, a deep understanding of the processes occurring at the BiVO 4 -H 2 O interface is crucial. Employing an electrochemical loading and removal process of NiO x , we show here that

more »

... ier 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 BiVO 4 photoelectrodes. At a bias of 1.23 V RHE , the Incident Photon-to-Current Efficiency (IPCE) at 450 nm reaches 43% for the passivated BiVO 4 electrode under back side illumination. A model incorporating heterogeneity of NiO x centers on the BiVO 4 surface (OER catalytic centers, recombination centers, and passivation centers) is proposed to explain this improved performance. † Electronic supplementary information (ESI) available: The reflection spectrum of the mirror for the illumination setup, the CVs for the characterization of BiVO 4 films in NaPi and NaBi, the light transmission spectrum of the BiVO 4 film, the CVs for NiO x loading and removal onto the FTO substrate, the XPS spectra of BiVO 4 films, and comparison of the photoresponse of BiVO 4 with/without the sulfite hole scavenger. See