Theoretical Insights into the Mechanism of Selective Nitrate-to-Ammonia Electroreduction on Single-Atom Catalysts

Selective nitrate-to-ammonia electrochemical conversion is an efficient pathway to solve the pollution of nitrate and an attractive strategy for low-temperature ammonia synthesis. However, current studies for nitrate electroreduction (NO₃RR) mainly focus on metal-based catalysts, which remains challenging because of the poor understanding of the catalytic mechanism. Herein, taking single transition metal atom supported on graphitic carbon nitrides (g-CN) as an example, the NO₃RR feasibility of single-atom catalysts (SACs) is first demonstrated by using density functional theory calculations. The results reveal that highly efficient NO₃RR toward NH₃ can be achieved on Ti/g-CN and Zr/g-CN with low limiting potentials of −0.39 and −0.41 V, respectively. Furthermore, the considerable energy barriers are observed during the formation of byproducts NO₂, NO, N₂O, and N₂ on Ti/g-CN and Zr/g-CN, guaranteeing their high selectivity. This work provides a new route for the application of SACs and paves the way to the development of NO₃RR.