Stabilizing Layered BiOBr Photoelectrocatalyst by Van Der Waals Heterojunction Strategy

BiOBr is a 2D layered material studied as photoelectrocatalyst for its suitable band gap for light absorption. However, its application in HER is not commonly reported, for unstable cathodic behavior, driven by a tendency to reduction to metallic bismuth. To solve this problem, 2D MoS2 is used to induce the formation of a van der Waals layered heterojunction to stabilize the lattice of BiOBr during HER. By performing PEC HER with the HJs containing different ratios of MoS2, it is found that the HJ with 1% MoS2 can increase the stability of BiOBr, while the one with 50% MoS2 can even accelerate the reduction of BiOBr to metallic bismuth. DFT calculations reveal the BioBr and MoS2 interface in the HJ with 1% MoS2 tends to push electrons on sulfur atoms, thus favoring HER. On the other hand, in the 50% HJ, active electrons are prone to react with BiOBr to induce reduction. In situ wide-angle X-ray diffraction (WAXD) allows to track the phase change and the phase transfer speed of BiOBr during PEC HER: under UV, a lower amount of BiOBr is reduced to Bi under negative potential, due to the presence of photogenerated holes reacting with the extra electrons.