Mechanistic exploring the catalytic activity of single-atom catalysts anchored in graphitic carbon nitride toward electroreduction of nitrate-to-ammonia

Electroreduction of water-pollutant nitrate to valuable ammonia provides a green and efficient route for low-temperature NH3 production instead of the convention Haber-Bosch process. However, finding robust catalysts for achieving nitrate to ammonia conversion remains a challenge due to the lack of a mechanistic view on the highly complex nitrate reduction and NH3 selectivity. Herein, we systematically investigate electrocatalytic activity and NH3 selectivity of a single-atom catalyst supported on graphitic carbon nitride (TM/g-C3N4) for nitrate reduction reaction (NO3RR) using first-principles calculations. Our results reveal that Ti/g-C3N4, V/g-C3N4, and Nb/g-C3N4 serve as the most promising NO3RR catalysts, as they exhibit stability, excellent activity, high selectivity (Faradaic efficiency of ∼ 100%), and low limiting potential (−0.42, −0.25, and −0.40 V for Ti/g-C3N4, V/g-C3N4, and Nb/g-C3N4, respectively). In addition, considerable potential energy barriers are found in the formation of byproducts NO2, NO, and N2O, validating their high selectivity. Nitrate to ammonia conversion is more competitive than hydrogen evolution reaction on TM/g-C3N4 owning to a lower limiting potential. This work reveals the structure dependence of NO3RR reaction pathways in single-atom catalysts and opens a new avenue for designing more efficient catalysts for NO3RR under ambient conditions.