Theoretical insights into the electroreduction of nitrate to ammonia on graphene-based single-atom catalysts

Electrocatalytic reduction of harmful nitrate (NO 3 − ) to valuable ammonia (eNO 3 RR) is critical and attractive for both environmental remediation and energy transformation. A single atom catalyst (SAC) based on graphene represents one of the most promising eNO 3 RR catalysts. However, the underlying catalytic mechanism and the intrinsic factors dictating the catalytic activity trend remain unclear. Herein, using first-principles calculations, eNO 3 RR on TMN 3 and TMN 4 (TM = Ti-Ni) doped graphene was thoroughly investigated. Our results reveal that FeN 4 doped graphene exhibits excellent eNO 3 RR performance with a low limiting potential of −0.38 V, agreeing with the experimental finding, which can be ascribed to the effective adsorption and activation of NO 3 − via the charge "acceptance-donation" mechanism and its moderate binding due to the occupation of the d-p antibonding orbital. In particular, we found that eNO 3 RR activities are well correlated with the intrinsic properties of TM centers and their local environments. With the established activity descriptor, several other graphene-based SACs were efficiently screened out with excellent eNO 3 RR performance. Our studies could not only provide an atomic insight into the catalytic mechanism and activity origin of eNO 3 RR on graphene-based SACs, but also open an avenue for the rational design of SACs for eNO 3 RR towards ammonia by regulating the metal center and its local coordination environment. The catalytic mechanism, activity trend, and activity origin of electroreduction of nitrate to ammonia on graphene-based single-atom catalysts was systematically studied and unrevealed.