Theoretical Investigation of Electrocatalytic Reduction of Nitrates to Ammonia on Highly Efficient and Selective g-C 2 N Monolayer-Supported Single Transition-Metal Atoms.

Electrocatalytic reduction of nitrate (NO 3 RR) to synthesize ammonia (NH 3 ) can effectively degrade nitrate while producing a valuable product. By utilizing density functional theory calculations, we investigate the potential catalytic performance of a range of single transition-metal (TM) atoms supported on nitrogenated holey doped graphene (g-C 2 N) (TM/g-C 2 N) for the reduction of nitrates to NH 3 . Based on the screening procedure, Zr/g-C 2 N and Hf/g-C 2 N are predicted as potential electrocatalysts for the NO 3 RR with limiting potential ( U L ) values of -0.28 and -0.27 V, respectively. The generation of byproducts such as dioxide (NO 2 ), nitric oxide (NO), and nitrogen (N 2 ) is hindered on Zr/g-C 2 N and Hf/g-C 2 N due to the high energy cost. The NO 3 RR activity of TM/g-C 2 N is closely related to the adsorption free energy of NO 3 - . The study not only proposes a competent electrocatalyst for enhancing NO 3 RR in ammonia synthesis but also provides a comprehensive understanding of the NO 3 RR mechanism.