Synergistic effect of multi-metal site provided by Ni-N₄, adjacent single metal atom, and Fe₆ nanoparticle to boost...

Single transition metal (TM) atom embedded in nitrogen-doped carbon materials with M-N_x-C configuration have emerged as a promising class of electrocatalysts for electrochemical CO₂ reduction (CO₂RR). However, at high TM atom densities, a comprehensive understanding of the active site structure and reaction mechanisms remains a significant challenge, yet it is crucial for enhancing CO₂RR performance. In this work, we use first-principles calculations to investigate the electrocatalytic performance of Ni-N₄ sites for CO2 reduction to CO, co-assisted by neighboring TM atoms and a Fe₆ nanoparticle. Unlike many previously studied Ni-N₄ catalysts that maintain a linear CO₂ structure, the combination of adjacent TM atoms and Fe₆ induces bending and activation of CO₂ at the Ni site, enhancing its protonation to form key *COOH intermediate while maintaining efficient *CO desorption. The newly designed hybrid electrocatalyst demonstrates a synergistic effect of multi-metal sites in boosting CO₂ reduction to CO. Specifically, the TM atom facilitates C-Ni bond formation between the Ni site and *CO₂/*COOH species, while Fe₆ forms an Fe…O coordination bond. Detailed analysis of reaction mechanisms and energetics show that Ni-N₄, co-assisted by a single TM atom and Fe₆ (especially TM = Ni, Cu, or Ag), exhibits enhanced catalytic activity for CO production with a low limiting potential of -0.5 V. This work presents an effective strategy for improving the catalytic activity of single-atom catalysts (SACs) at high metal content.