Molecular-Fence Confinement Enabling Efficient Acidic CO₂ Electroreduction to Multi-carbon Products

Acidic CO₂ electroreduction (CO₂ER) enhances carbon utilization but faces significant challenges: intense hydrogen evolution reaction competition and poor multicarbon (C₂₊) product selectivity. We identify that this stems primarily from acid-induced destabilization of the critical *CO intermediate, exacerbated by adsorbed hydrogen. Here, we propose a dual-modification "molecular-fence" strategy to reconfigure the catalyst-electrolyte interface. We first engineer atomically dispersed Lewis acid Zr sites on Cu to electronically accelerate *CO formation. Subsequently, we anchor π-conjugated benzo-2,1,3-thiadiazole (BTD) molecules, which form a physical fence that spatially confines *CO intermediates and electrogenerated OH^-. This synergy creates and sustains a localized, highly alkaline microenvironment in bulk acidic media, which concentrates *CO coverage and strengthens *CO binding to accelerate C-C coupling kinetics for acidic CO₂ER. As a result, we achieve Faradaic efficiencies of 57.0% for ethylene (C₂H₄) and 74.9% for total C₂₊ products at 600 mA cm^-2. Single-pass carbon efficiencies reach 64.2% for C₂H₄ and 79.9% for C₂₊. Remarkably, a high C₂H₄ selectivity (>52.0%) is sustained across a wide current density range of 400 to 700 mA cm^-2. This work establishes the molecular-fence strategy as a broadly applicable paradigm for regulating interfacial microenvironments to enable efficient and selective CO₂ER in challenging acidic media.