Isomerization-Guided Trace Sulfur Doping Enables Selective CO₂-to-Ethanol Conversion

Directing the CO₂ reduction reaction (CO₂RR) toward ethanol offers a promising route to sustainable liquid fuels. However, achieving high ethanol selectivity under industrially relevant current densities still remains a major challenge. Here, we introduce trace sulfur doping via thiourea isomerization, which enables precise sulfur incorporation to weakly bind bridge-adsorbed OH species, thereby suppressing OH⁻ adsorption on active sites and preventing their attack on defect sites. In situ Raman spectroscopy further reveals that suppressed OH⁻ adsorption promotes the exposure of undercoordinated Cu active sites, enabling robust *CO atop-binding configurations to be sustained, particularly under strongly cathodic current densities. Additionally, the tailored surface microenvironment boosts *CO dimerization kinetics, and its synergistic interplay with *OH modulation channels the reaction pathway toward ethanol generation. Consequently, the catalyst delivers a current density of −0.9 A cm⁻² with a Faradaic efficiency of nearly 79.6% for C₂₊ products, including 40% toward ethanol. This work highlights trace heteroatom-driven surface reconstruction as an effective strategy to engineer catalytic CO₂ utilization.