Photocatalytic Nitrogen Reduction Reaction over Two-Dimensional Cs₃Bi₂Br₉–CdS Van der Waals Heterostructures by External Control Strategies

The green and sustainable photocatalytic nitrogen reduction reaction (NRR) for ammonia generation under ambient conditions holds great promise. One of the most serious challenges is to improve the efficiency of catalysts. In this study, an effective photocatalytic NRR has been developed by using density functional theory (DFT) calculations, in which a two-dimensional Cs₃Bi₂Br₉–CdS van der Waals heterostructure is applied as the photocatalyst and functioned under external control strategies. The calculated results show that the heterojunction has a type-II band alignment, and the unique built-in electric field lowers the band gap, enhances the light absorption, and decreases the effective mass compared to those of a single component. In addition, when applying an external electric field up to 0.27 V/Å, the normal type-II band alignment is transformed into type-Z band alignment, thus improving carrier separation and maintaining high redox potential. From the exploration of surface catalytic performance, it was found that the nitrogen–nitrogen bond is activated by the strong nitrogen adsorption and electron transfer, and the lower overpotential theoretically indicates an excellent catalytic performance. This work not only provides a feasible strategy for improving the NRR performance of photocatalysts, but also interprets the reaction mechanism at the electronic level.