Van der Waals Epitaxial Growth of Two-Dimensional BiOBr Flakes with Dendritic Structures for the Hydrogen Evolution Reaction

Two-dimensional (2D) layered ternary compounds have attracted tremendous interest in recent years, owing to their intriguing physical and chemical properties. However, the controllable synthesis of 2D ternary crystals with various structures remains a great challenge. Here, we report the successful synthesis of 2D bismuth oxybromide (BiOBr) flakes with compact square shapes and dendritic structures via van der Waals epitaxy. By tuning the growth parameters, the shapes of the 2D BiOBr flakes can be tuned from compact squares to dendritic structures. The branch length of the dendritic structure can reach ∼200 μm, about 10 times larger than that of the compact square BiOBr flakes with a typical size of 10-20 μm. Owing to their abundant edges, the photocurrent density of the dendritic BiOBr flakes in the hydrogen evolution reaction increases 0.077 mA/cm2 (coverage of ∼12%) compared to that in the dark condition at -0.3 V versus the reversible hydrogen electrode in an acid environment, which is about 3 times higher than that of the compact counterpart (0.022 mA/cm2, coverage of ∼13%). Our work sheds light on the preparation of 2D ternary materials with dendritic structures in application of high-performance catalysts.