Anion surfactant-tailored electric double-layer: Toward higher faradaic efficiency in acidic CO2 electrolysis

Electric double-layer (EDL) structure critically influences electrocatalytic kinetics and performance, yet mechanistic understanding of anion-mediated EDL modulation remains limited, particularly in acidic CO 2 electrolysis. Here, we demonstrate that the prototypical anionic surfactant sodium dodecyl sulfate (SDS) induces EDL expansion and reconstruct interfacial hydrogen-bonding (H-bond) networks, thereby suppressing the competitive hydrogen evolution reaction (HER) in acidic electrolytes, while achieving 94.1% CO Faradaic efficiency at 250 mA cm –2 . Electrochemical kinetics analysis identifies that SDS-induced disruption of interfacial H-bond networks impedes proton transport kinetics, thereby suppressing HER in acid. Integrative electrolyte characterizations combined with in situ spectroscopic analysis revealed that the widening of the EDL stems from Lewis acid-base interactions between SDS and K + . Further, the introduction of SDS modulates interfacial water dissociation activity, thereby facilitating the hydrogenation pathway from CO 2 to *COOH. These findings establish a rational electrolyte design strategy for manipulating EDL to enhance acidic CO 2 electrolysis performance.