Previous studies have demonstrated that oxidized Cuδ+ species as real active sites can significantly enhance C2+ selectivity. However, at high current densities, active Cuδ+ species are readily reduced to metallic Cu, resulting in a loss of activity. Thus, stabilizing active Cuδ+ species in industrial-scale ECR reactions poses significant challenges. In this study, we use activated carbon black with various functional groups to modulate the interface microenvironment of Cu NPs, aiming to increase CO coverage and inhibit HER. Various in situ characterizations reveal that in situ generated strongly oxidative hydroxyl species create a locally oxidative microenvironment on the catalyst surface, stabilizing oxidized Cuδ+ species and promoting the evolution of morphology and valence state of high-curvature nanowhiskers. Consequently, we achieve 55.6% ± 2.8 ethylene selectivity at a current density of 316 mA cm−2.