<p>Electrochemical reduction of CO₂ to valuable C1 products is a promising strategy for carbon mitigation and renewable energy storage. Copper-based single-atom catalysts have garnered significant attention due to their exceptional catalytic performance for CO₂ reduction reactions. In this study, we used density functional theory to systematically investigate the effect of heteroatom (B, O, S) doping on Cu–N–C SACs. By adjusting the coordination environment of Cu active sites, we aimed to enhance the catalytic efficiency and selectivity for C1 products, such as CO, HCOOH, CH₃OH, and CH₄. Our results reveal that doping with heteroatoms significantly modulates the electronic structure of the Cu active sites, thereby influencing CO₂ adsorption, intermediate stabilization, and reaction pathways. The S-doped Cu-N₂S₂-1 and Cu-N₂S₂-2 catalysts exhibit superior CO selectivity, while B-doped Cu-N₂B₂-2 and Cu-N₁B₃ catalysts demonstrate high HCOOH production efficiency. The Cu-N₂B₂-1 catalyst shows optimal activity for multi-electron products (CH₃OH and CH₄), while Cu-N₁B₃ and Cu-N₀O₄ display superior selectivity for CH₃OH and CH₄, respectively. Stability analyses confirm the structural and electrochemical robustness of these catalysts under operating conditions. This work provides critical insights into the coordination engineering of Cu SACs and establishes a rational design strategy for high-performance catalysts in sustainable CO₂ conversion.</p>