Nitrate reduction reaction on single-atom catalysts supported on 3N-coordinated nitrogen-doped graphene

Utilizing nitrate (NO3−) as the nitrogen source to produce ammonia can effectively remove NO3− pollutant while obtaining valuable ammonia, and the understanding of the mechanisms is essential for the design of new catalysts. In this work, by using density functional theory calculations, the electroreduction mechanisms of nitrate reduction reaction (NO3RR) on transition metal single atom supported on 3N-coordinated N-doped graphene (TM/N3-G) are systematically investigated. It is found that the protonation of *OH acts as the potential determing steps except for the traditionally considered *NO3/*NO/*NO2 protonation step and the desorption of water may play an important role for NO3RR on some TM/N3-G. By considering the stability of single-atom catalyst (SAC), the preferential adsorption of NO3− larger than H and H2O, the limiting potential of whole NO3RR, the selectivity toward NH3, V (Mn, Os)/pyrrolic-N3-G and Mn (Ru, Ir)/pyridinic-N3-G are screened out as potential SACs for NO3RR. This work provides an understanding of the NO3RR mechanism and highlights several promising NO3RR catalysts based on the TM/N3-G system.