Revealing a power-law relationship between dopant-metal distance and adsorption free energy change for precise optimization of the ORR on TM1N4 single-atom catalysts

Abstract

Studying the influence of the distance between dopant and transition metal (TM) atom (d_TM–N) on the local atomic/electronic structures of the active centers is beneficial for fine-tuning the catalytic performance toward optimal efficiency. In this work, the oxygen reduction reaction (ORR) activity and selectivity of TM₁N₄@carbon single-atom catalysts (TM = Fe, Co and Ni) were systematically modulated by adjusting the d_TM–N values using density functional theory simulations. The results show that nitrogen doping at any position lowers the d-band center, thereby enhancing d–p orbital hybridization, reducing chemical activity, and increasing adsorption free energy. The difference in adsorption free energy (ΔG_doped − ΔG_pristine) is mainly determined by both the nature of the adsorbed species and the type of TM atom, with clear power-law relationships identified between these factors. The catalytic performance of TM₁N₄@carbon is primarily governed by the intrinsic chemical activity of the TM atoms and can be further optimized through precise control of d_TM–N. With appropriate nitrogen doping, Co₁N₄@carbon exhibits exceptionally low ORR overpotentials for the two-electron path (η^2e = 0.018 V and 0.026 V when nitrogen is doped at positions 1 and 2, respectively). This approach offers a promising strategy for the rational design of high-activity and selectivity single-atom catalysts.