Stepped copper sites coupling voltage-induced surfactant assembly to achieve efficient CO2 electroreduction to formate†

The electrochemical reduction of carbon dioxide (CO₂) into formate holds great promise. However, the ongoing competition of parallel reactions, including the generation of hydrogen (H₂), carbon monoxide (CO), and multi-carbon products, continues to be a significant factor influencing the formate selectivity. Here, we report a copper-based heterojunction (Cu₂O@Cu) precatalyst, which undergoes significant structural reconstruction, resulting in the formation of stepped Cu sites on a hierarchical dendritic array. The formate selectivity of reconstructed Cu₂O@Cu can achieve up to 95.9% at a low potential of −0.6 V versus the reversible hydrogen electrode when quaternary ammonium cationic surfactants are introduced. Meticulous in situ spectroscopic and theoretical analyses reveal that the electrically driven alignment of surfactants not only repels hydrated ions, thereby inhibiting proton delivery in H₂ evolution, but also interacts with stepped Cu sites to deactivate CO and C–C coupling pathways. The electrified modulation of interfacial microenvironment ultimately suppresses the evolution of H₂, CO, and multi-carbon products, ensuring the high-selectivity conversion of CO₂ to formate. This study highlights the crucial synergistic effect of structural reconstruction and ligand modification in enhancing electrocatalysis.