A coordination environment effect of single-atom catalysts on their nitrogen reduction reaction performance

Understanding the structure-activity relationship of an active site is of great significance toward the rational design of highly active catalysts. In this study, we have performed density functional theory calculations to investigate the coordination environment effect of Fe-, N-, and O-doped carbon on their nitrogen reduction reaction (NRR) properties. Our results indicate that the presence of O atoms in the coordination environment favors the activation of N-2 molecules but is unfavorable to the stability, while the existence of N will weaken the adsorption of N-2 and increase the reaction barrier of the first hydrogenation step. Fe-C-4-C has the lowest potential for activating N-2. A compromise is Fe-NxC4-x-C, where the interaction of C and N in coordination regulates the spin polarization of Fe and thus the 3d states around the Fermi level. Fe-N2C2-C was found to be the best one and NRR can proceed via the distal and alternative reaction pathways with the first hydrogenation step of N-2 being the potential-limiting step and the Gibbs free energy change (Delta G) being 0.75 eV.