Computational Screening of High Activity and Selectivity TM/g-C3N4 Single-Atom Catalysts for Electrocatalytic Reduction of Nitrates to Ammonia.

Electrocatalytic reduction of nitrates (NO3RR) selectively generating ammonia (NH3) opens up a new idea for treating nitrates in wastewater, which not only reduces nitrates but also obtains the valuable product ammonia. By first-principles calculations, we explore the activity and selectivity for NO3RR to NH3 of TM/g-C3N4 single-atom catalysts. Six TM/g-C3N4 catalysts (TM = Ti, Os, Ru, Cr, Mn, and Pt) are selected by a four-step screening method. Ru/g-C3N4 is the most promising of these six TM/g-C3N4 catalysts because of its lowest energy barrier and extraordinary selectivity. The origin of the NO3RR activity of Ru/g-C3N4 is explained from the viewpoint of NO3- adsorption. In addition, the hydrogen evolution reaction has also been implied to be uncompetitive for the poor adsorption on H atoms. This work provides a screening mechanism for finding new catalysts for NO3RR to NH3, promotes the development of NO3RR, and provides a stimulating impetus for further experimental exploration.