Single-Atom Catalysts for CO₂ Reduction to Oxalate: Theoretical Design and Reaction Condition Prediction

The electrochemical conversion of carbon dioxide (CO₂) into high-value-added products under mild conditions is crucial for achieving carbon neutrality. Oxalate (C₂O₄^2-) is one of the most important industrial raw materials and is widely used as a reducing agent in the fields of medicine, dyeing, and plastics yet faces challenges in efficient C-C bond formation under mild conditions. In this study, we investigate the reduction of CO₂ to C₂O₄^2- using single-atom catalysts (SACs) with M-N_x-C configurations, employing density functional theory (DFT) to assess their catalytic performance under varying reaction conditions. Our findings demonstrate that the catalytic activity of Ti-N₃-C is highly sensitive to the choice of solvent and electrode potential. Lower solvent dielectric constants and more negative electrode potentials promote oxalate formation with Ti-N₃-C, exhibiting a remarkably low-energy barrier (0.31 eV) for the rate-determining step at -0.7 V in acetonitrile, alongside high selectivity. By systematically tuning the coordination environment of single metal atoms, we identify Ti-N₂C-C, Cr-N₂C-C, and Cr-N₃-C as promising catalysts, operating efficiently at potentials of -0.7, -0.7, and -0.6 V, respectively. This work not only offers theoretical guidance for designing high-performance SACs for CO₂ conversion but also deepens the mechanistic understanding of the electrochemical CO₂ reduction pathways.