• • F doping into La2CuO4 increases C2+ Faradaic efficiency from 41.7% (undoped LC) to 73.0% at −1.2 V vs. RHE, a 31.3 percentage point gain that directly improves carbon utilization and product value in CO2 electrolyzers.
• • The F-LC catalyst achieves this selectivity by lowering the energy barrier for asymmetric *CO–*CHO coupling, as evidenced by the preferential formation of *CHO intermediates detected via in situ spectroscopy, enabling a more efficient PCET pathway.
• • Interfacial H2O dissociation is accelerated through hydrogen bonding interactions at F sites, generating abundant *H species that drive *CO hydrogenation while suppressing HER, as reflected by a 1.8-fold increase in C2+ partial current density relative to LC.
• • The dense hydrogen-bond network on F-LC reorganizes interfacial water and enhances proton transfer, reducing the overpotential for C2+ formation by approximately 150 mV compared to undoped LC, which translates to lower energy input per ton of product.