Theoretical Investigation of Electrocatalytic Reduction of Nitrates to Ammonia on Highly Efficient and Selective g-C2N Monolayer-Supported Single Transition-Metal Atoms

Electrocatalytic reduction of nitrate (NO3RR) to synthesize ammonia (NH3) 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-C2N) (TM/g-C2N) for the reduction of nitrates to NH3. Based on the screening procedure, Zr/g-C2N and Hf/g-C2N are predicted as potential electrocatalysts for the NO3RR with limiting potential (UL) values of -0.28 and -0.27 V, respectively. The generation of byproducts such as dioxide (NO2), nitric oxide (NO), and nitrogen (N2) is hindered on Zr/g-C2N and Hf/g-C2N due to the high energy cost. The NO3RR activity of TM/g-C2N is closely related to the adsorption free energy of NO3-. The study not only proposes a competent electrocatalyst for enhancing NO3RR in ammonia synthesis but also provides a comprehensive understanding of the NO3RR mechanism.