Photoelectrodes Based upon Mo:BiVO₄ Inverse Opals for Photoelectrochemical Water Splitting

D rawing inspiration from nature, photoelectrochemical (PEC) water splitting based on Fujishima Honda effect has been demonstrated as a feasible and cost-effective realization of an artificial analogy to photosynthesis. 7 With the goal of solar energy harvesting and storage, semiconductor photoelectrodes hold great promise to be an attractive alternative to the naturally occurring photosystems. In spite of intense research efforts, progress in this domain seems relatively slow because it is hard to find an ideal material that originates from the competing nature of its intrinsic properties. Among all the widely investigated photocatalysts, monoclinic scheelite BiVO4 is a promising candidate after striking a balance among various intrinsic features due to its suitable band gap, proper band location, great stability, and environment friendliness. Despite these attractive characteristics, BiVO4 still suffers from several challenging technical points for large-scale implementations. The primary one is a relatively low mobility of photogenerated charges, which would naturally hinder the separation of electron hole pairs and consume some solar conversion efficiency. Accordingly, even from the viewpoint of a perfect bulk singlecrystalline BiVO4, both calculated and experimental 13 results indicate that alleviating chargemigration problems, including surface charge transfer and bulk charge transport, shows a significant scope for improving the performance of PEC water splitting. In general, charge migration is strongly affected by the crystal structural features and themorphology of a photoelectrode. To meet the challenge of low charge migration in BiVO4 photoelectrodes, first, we can regulate the composition by doping to increase the electronic conductivity intrinsically. For example, incorporation of Mo6þ into the partial sites of V5þ in BiVO4 can change the crystal symmetry of BiVO4 and introduce some polarons, both of which would benefit for higher charge carrier concentration. 20 Second, another efficient way to improve charge migration is to reduce the charge recombination during drift, diffusion, and surface transfer processes. * Address correspondence to [email protected], [email protected].