Different Crystal Facet Coupling Effects on the Photocatalytic Properties of BiOX/BiVO₄ (X = Cl, Br, I) Heterostructures: A First-Principles Study

Different crystal facet combinations could greatly influence the type and photocatalytic performance of heterojunctions, but the impacts on BiOX/BiVO 4 (in this study, X = Cl, Br, I) remain unclear. Therefore, in this paper, the more easily exposed BiOX(001) and (010) crystal facets are combined with the more easily exposed BiVO 4 (001) crystal facet to explore the gap in theory. The accurate electronic structure calculations indicate that BiOCl(001)/BiVO 4 (001) and BiOBr(001)/BiVO 4 (001) form the undesired type-I heterojunctions, while BiOI(001)/BiVO 4 (001) forms a favorable direct Z-scheme heterojunction, exhibits a stronger ability to separate photogenerated electrons and holes, and has better photocatalytic performance. However, BiOX(001)/BiVO 4 (001) suffers from an insufficient reduction capacity. Contrastively and excitedly, all BiOX(010)/BiVO 4 (001) combinations are direct Z-scheme heterojunctions and possess higher separation efficiency for photogenerated electrons and holes, stronger reduction abilities, and smaller band gaps (meaning better visible light absorption). Therefore, the static electronic structure calculations clearly illustrate that BiOX(010)/BiVO 4 (001) combinations’ photocatalytic performances are obviously superior to the corresponding ones of BiOX(001)/BiVO 4 (001) combinations. However, among all heterojunctions, the BiOI(010)/BiVO 4 (001) heterojunction has larger lattice mismatch rates, reducing the photocatalytic activity and complicating the experimental preparation. Further, the actual photocatalytic performances of the direct Z-scheme BiOI(001)/BiVO 4 (001), BiOCl(010)/BiVO 4 (001), and BiOBr(010)/BiVO 4 (001) heterojunctions surpass that of BiOI(010)/BiVO 4 (001), while BiOBr(010)/BiVO 4 (001) presents the best photocatalytic activity. These theoretical results excellently explain the related experiments. Undoubtedly, the effects of different crystal facet combinations on the photocatalytic performance of BiOX/BiVO 4 heterostructures must be carefully considered to clarify experimental controversies and guide the preparation of high-performance BiOX/BiVO 4 heterostructure photocatalysts.