Theoretical study on single-atom catalysts for N2 electroreduction

Abstract

In this study, we studied nitrogen reduction reaction (NRR) on single atom catalyst (SAC) theoretically. Four SACs at defected graphene were modelled, metal atom on carbon defect sites $(M@C_3, M@C_4)$ and nitrogen defect sites $(M@C_3, M@C_4)$. We calculate reaction free energies of NRR on SACs by using DFT calculations and compared with those on metal surfaces. Many SACs show higher NRR selectivity than metal surfaces. Hydrogen evolution reaction (HER) is highly suppressed on SACs. Several SACs show lower limiting potential than Ru (0001) stepped surface. In particular $La@N_3$ (-0.72V) and $Ti@N_4$ (-0.80V) show significantly low limiting potential. To understand the origin of suppressed HER, we found that lack of atomic ensemble for $\ast H$ can highly destabilize $\ast H$ on SACs. Several SACs including $Ti@N_4$ show enhanced $\ast N_2$ adsorption. The different electronic structure of SAC from that of metal surface can play an important role in orbital interactions between metal and $\ast N_2$.