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

Ammonia (NH3) splitting to hydrogen (H-2)is a promising route for on-site production of green hydrogen energy;however, the application is limited due to high-cost noble-metal-basedcatalysts and high operating temperature of the endothermic nature.Herein, we develop a series of macroporous carbon nitride-supportedsingle-atom transition metal (TMs-MCN, TMs: Co, Mn, Fe, Ni, Cu) catalystpanels for solar light-driven photocatalytic gaseous NH3 splitting. Under ambient reaction conditions, the optimized Ni-MCNshows an H-2 production rate of 35.6 & mu;mol g(-1) h(-1), much superior to that of MCN and other TMs-MCN.Such enhanced photoactivity is attributed to the presence of Ni-N-4 sites, which improve the optical properties, accelerate chargecarrier separation/transfer, and boost NH3 splitting kineticsof the catalysts. Density functional theory calculations further revealthat the Ni-N-4 sites can effectively modify theelectronic structure of the carbon nitride. Compared with other metalsites, the Ni-N-4 site possesses moderate NH3 binding strength and the lowest energy barrier to facilitatethe formation of key intermediates *NH + *H. These findings providevaluable guidelines for the rational design of single-atom catalyststoward energy- and cost-effective photocatalytic NH3 splittingfor H-2 production.