Core−shell structured Bi/BiOBR photoelectrodes for efficient photoelectrochemical water splitting

Two-dimensional ternary compounds bismuth oxyhalides (BiO_xBr_y) with suitable band gap and high surface bulk ratio have great potentials for photoelectrochemical water splitting. Although intensive efforts were devoted to the design of well-defined nanostructures to optimize the photoreactivity, it remains a great challenge to improve the light absorption capacity and charge carrier transfer of the materials. In this work, we developed a controllable synthesis route to prepare core−shell structured Bi/ BiOBr complexes with abundant conduction channels and active edges as photoelectrodes. The structure and morphology of the Bi/BiOBr complexes could be modulated by tuning the thickness of Bi thin film and/or the oxygen gas flow during the annealing process. Photoelectrochemical analyses indicated that the photocurrent density of the Bi/BiOBr electrodes reached up to 0.36 mA cm⁻² at −0.4 V versus reversible hydrogen electrode (RHE) in acid environments, which was 1 order large than that based on pure BiOBr thin film electrodes (0.08 mA cm⁻²). Our study demonstrates that the controllable synthesis of Bi/BiOBr core−shell structures may open a new way for engineering 2D layered ternary compounds materials to develop novel catalyst devices.