Revisiting the role of foreign atoms in CO2 reduction on CuSn single-atom surface alloys

The electrochemical ${\mathrm{CO}}_2$ reduction is a promising process for capturing the emitted carbon dioxide by converting ${\mathrm{CO}}_2$ into value-added chemicals. Although copper-based catalysts have a unique ability to produce multi-carbon products, they suffer from poor selectivity. Copper-based alloys and, in particular, single atom alloys, hold promise for fine-tuning the selectivity of ${\mathrm{CO}}_2$ reduction reaction. In this study, we applied the grand canonical density functional theory in combination with the implicit solvent to model ${\mathrm{CO}}_2$ electroreduction with the formation of CO and ${\mathrm{HCOO}}^{-}$ on copper and highly diluted copper-tin alloys. We demonstrate that the insertion of a substitutional Sn atom introduces a destabilization effect for all intermediates and completely disrupts the adsorption positions of the CO, H, and H/${\mathrm{CO}}_2$ co-adsorption. However, the influence of Sn on intermediate adsorption energies is primarily localized in its immediate vicinity. We demonstrate that sparsely distributed single Sn atoms do not account for the experimentally observed significant reduction in formate and hydrogen generation across the entire Sn-substituted Cu surface. This discrepancy underscores the need to reevaluate the proposed surface structure and the nature of the active sites on CuSn single-atom surface alloys.