Membrane electrode assembly (MEA) electrolyzers offer a means to scale up CO -to-ethylene electroconversion using renewable electricity and close the anthropogenic carbon cycle. To date, excessive CO coverage at the catalyst surface with limited active sites in MEA systems interferes with the carbon-carbon coupling reaction, diminishing ethylene production. With the aid of density functional theory calculations and spectroscopic analysis, here we report an oxide modulation strategy in which we introduce silica on Cu to create active Cu-SiO interface sites, decreasing the formation energies of OCOH* and OCCOH*-key intermediates along the pathway to ethylene formation. We then synthesize the Cu-SiO catalysts using one-pot coprecipitation and integrate the catalyst in a MEA electrolyzer. By tuning the CO concentration, the Cu-SiO catalyst based MEA electrolyzer shows high ethylene Faradaic efficiencies of up to 65% at high ethylene current densities of up to 215 mA cm ; and features sustained operation over 50 h.