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.