Macroporous Carbon-Nitride-Supported Transition-Metal Single-Atom Catalysts for Photocatalytic Hydrogen Production from Ammonia Splitting

Ammonia (NH3) splitting to hydrogen (H2) is a promising route for on-site production of green hydrogen energy; however, the application is limited due to high-cost noble-metal-based catalysts and high operating temperature of the endothermic nature. Herein, we develop a series of macroporous carbon nitride-supported single-atom transition metal (TMs-MCN, TMs: Co, Mn, Fe, Ni, Cu) catalyst panels for solar light-driven photocatalytic gaseous NH3 splitting. Under ambient reaction conditions, the optimized Ni-MCN shows an H2 production rate of 35.6 μmol g–1 h–1, much superior to that of MCN and other TMs-MCN. Such enhanced photoactivity is attributed to the presence of Ni–N4 sites, which improve the optical properties, accelerate charge carrier separation/transfer, and boost NH3 splitting kinetics of the catalysts. Density functional theory calculations further reveal that the Ni–N4 sites can effectively modify the electronic structure of the carbon nitride. Compared with other metal sites, the Ni–N4 site possesses moderate NH3 binding strength and the lowest energy barrier to facilitate the formation of key intermediates *NH + *H. These findings provide valuable guidelines for the rational design of single-atom catalysts toward energy- and cost-effective photocatalytic NH3 splitting for H2 production.