Theoretical insights into the performance of single and double transition metal atoms doped on N-graphenes for N2 electroreduction

Single- and double-atom catalysts are normally with high activity and selectivity in N2 electroreduction. However, the properties of impacting their catalytic performances in N2 reduction are still unclear. In order to gain insights into the factors that influence their performances, we have theoretically studied N2 activation and reduction on eight catalysts, including two single-atom catalysts with Mn/Fe supported on nitrogen doped graphenes (N-graphenes), and six double-atom catalysts in which Mn and Fe atoms form three non-bonded centers (Mn⋯Mn, Fe⋯Fe and Mn⋯Fe) and three bonded centers (Mn-Mn, Fe-Fe and Mn-Fe) on N-graphenes. Our calculational results indicate that the two single-atom catalysts and the three non-bonded double-atom catalysts can’t efficiently activate N2 or convert it into NH3, whereas the bonded double-atom catalysts can not only efficiently activate but also convert N2 at low overpotentials. Especially, the bonded Mn-Fe catalyst is found to be the most efficient catalyst due to its very lower overpotential (0.08 V) for N2 reduction reaction among the eight catalysts. Moreover, the charge analysis revealed that the electron-donating capacities and the synergistic effects of the two bonded metal atoms are both responsible for the enhanced catalytic performances.