Theoretical Insights into Electrocatalytic Reduction of Nitrates to Ammonia on g-C ₂ N Monolayer-Supported Single Nonmetal Atoms

Electrochemical reduction of nitrate to ammonia is not only an effective strategy for dealing with nitrate pollution but also presents a promising alternative in the field of ammonia synthesis at low temperatures. Nevertheless, current research on nitrate reduction reactions (NO₃RR) has predominantly centered on metal catalyst systems, and owing to an incomplete understanding of the catalytic mechanism, the development of this field still faces significant challenges. This research employs density functional theory (DFT) computations to systematically explore the catalytic capability of single-atom nonmetallic catalysts (NM/g-C₂N) embedded in nitrogen-doped porous graphene (g-C₂N) for the reduction of nitrate to ammonia (NO₃RR-to-NH₃). Findings reveal that Si/g-C₂N and As/g-C₂N systems showcase remarkable electrocatalytic activity for NO₃RR, with limiting potentials for ammonia synthesis as low as -0.23 V and -0.31 V, respectively. Crucially, higher energy barriers effectively inhibit the formation of byproducts (NO₂⁻, NO, N₂), thereby boosting ammonia synthesis selectivity. Additionally, the hydrogen evolution reaction (HER) is thermodynamically suppressed due to weak hydrogen adsorption on the catalyst surface. This study not only discovers a new type of NO₃RR catalyst but also provides new ideas and methods for designing novel NO₃RR catalysts.