Promoting effect of interfacial hole accumulation on photoelectrochemical water oxidation in BiVO4 and Mo-doped BiVO4

Hole transfer at the semiconductor-electrolyte interface is a key elementary process in (photo)electrochemical (PEC) water oxidation. However, up to now, a detailed understanding of the hole transfer and the influence of surface hole density on PEC water oxidation kinetics is lacking. In this work, we propose a model for the first time in which the surface accumulated hole density in BiVO 4 and Mo-doped BiVO 4 samples during water oxidation can be acquired via employing illumination-dependent Mott-Schottky measurements. Based on this model, some results are demonstrated as below: (1) Although the surface hole density increases when increasing light intensity and applied potential, the hole transfer rate remains linearly proportional to surface hole density on a log-log scale. (2) Both water oxidation on BiVO 4 and Mo-doped BiVO 4 follow first-order reaction kinetics at low surface hole densities, which is in good agreement with literature. (3) We find that water oxidation active sites in both BiVO 4 and Mo-doped BiVO 4 are very likely to be Bi 5+ , which are produced by photoexcited or/and electro-induced surface holes, rather than VO x species or Mo 6+ due to their insufficient redox potential for water oxidation. (4) Introduction of Mo doping brings about higher OER activity of BiVO 4 , as it suppresses the recombination rate of surface holes and increases formation of Bi 5+ . This surface hole model offers a general approach for the quantification of surface hole density in the field of semiconductor photoelectrocatalysis. A surface hole model is proposed to determine the surface hole density in BiVO 4 photoanodes. Besides, the higher OER activity of Mo-doped BiVO 4 originates from its lower surface hole recombination rate. • A model is proposed to determine the surface accumulated hole density in BiVO 4 and Mo-doped BiVO 4 samples during water oxidation. • Water oxidation on BiVO 4 and Mo-doped BiVO 4 follow first-order reaction kinetics. • The higher OER activity of Mo-doped BiVO 4 originates from its lower surface hole recombination rate.