Regulation of H⁺ transfer pathways promotes C-C coupling in acidic CO₂ electroreduction

Electrochemical CO₂ reduction reaction in acidic media is fundamentally limited by competitive hydrogen evolution and poor selectivity toward multi-carbon products. Here we report a cooperative catalytic strategy that enables highly selective multi-carbon formation under strongly acidic conditions by regulating proton activation and interfacial solvation. By exploiting the copper oxide nanosheets and integrating an immobilized cobalt tetra(4-carboxyphenyl)porphyrin, a dual-functional interface is constructed that steers abundant protons toward productive C-C bond formation. This synergy sustains C-C coupling at high current densities and suppresses parasitic hydrogen evolution. As a result, the hybrid catalyst delivers a multi-carbon Faradaic efficiency of up to 89.5% with partial current densities exceeding 1 A cm^-2 in pH 2 ± 0.1 electrolyte, and maintains high selectivity even at pH 0.7 ± 0.05. Operando spectroscopic analyses and theoretical calculations reveal that regulated proton activation enables efficient formation of key C-C coupling intermediates and stabilizes the catalytic interface under acidic conditions. These results demonstrate a viable route to achieve efficient CO₂ electroreduction to multi-carbon products in acidic environments through molecular control of proton utilization.