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

The electrochemical conversion of carbon dioxide (CO 2 ) into high-value-added products under mild conditions is crucial for achieving carbon neutrality. Oxalate (C 2 O 4 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 CO 2 to C 2 O 4 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–N 3 –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–N 3 –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–N 2 C–C, Cr–N 2 C–C, and Cr–N 3 –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 CO 2 conversion but also deepens the mechanistic understanding of the electrochemical CO 2 reduction pathways.