CO ₂ electroreduction offers a route to net-zero-emission production of C ₂H ₄—the most-produced organic compound. However, the formation of carbonate in this process causes loss of CO ₂ and a severe energy consumption/production penalty. Dividing the CO ₂-to-C ₂H ₄ process into two cascading steps—CO ₂ reduction to CO in a solid-oxide electrolysis cell (SOEC) and CO reduction to C ₂H ₄ in a membrane electrode assembly (MEA) electrolyser—would enable carbonate-free C ₂H ₄ electroproduction. However, this cascade approach requires CO-to-C ₂H ₄ with energy efficiency well beyond demonstrations to date. Here, we present a layered catalyst structure composed of a metallic Cu, N-tolyl-tetrahydro-bipyridine, and SSC ionomer that enables efficient CO-to-C ₂H ₄ in a MEA electrolyser. In the full SOEC-MEA cascade approach, we achieve CO ₂-to-C ₂H ₄ with no loss of CO ₂ to carbonate and a total energy requirement of ~138 GJ (ton C ₂H ₄) ⁻¹, representing a ~48% reduction in energy intensity compared with the direct route.

The electrochemical reduction of carbon monoxide is a promising approach for the renewable production of carbon-based fuels and chemicals. Copper shows activity toward multi-carbon products from CO reduction, with reaction selectivity favoring two-carbon products; however, efficient conversion of CO to higher carbon products such as n-propanol, a liquid fuel, has yet to be achieved. We hypothesize that copper adparticles, possessing a high density of under-coordinated atoms, could serve as preferential sites for n-propanol formation. Density functional theory calculations suggest that copper adparticles increase CO binding energy and stabilize two-carbon intermediates, facilitating coupling between adsorbed *CO and two-carbon intermediates to form three-carbon products. We form adparticle-covered catalysts in-situ by mediating catalyst growth with strong CO chemisorption. The new catalysts exhibit an n-propanol Faradaic efficiency of 23% from CO reduction at an n-propanol partial current density of 11 mA cm⁻².