Cascade CO₂ electroreduction enables efficient carbonate-free production of ethylene

CO₂ electroreduction offers a route to net-zero-emission production of C₂H₄—the most-produced organic compound. However, the formation of carbonate in this process causes loss of CO₂ and a severe energy consumption/production penalty. Dividing the CO₂-to-C₂H₄ process into two cascading steps—CO₂ reduction to CO in a solid-oxide electrolysis cell (SOEC) and CO reduction to C₂H₄ in a membrane electrode assembly (MEA) electrolyser—would enable carbonate-free C₂H₄ electroproduction. However, this cascade approach requires CO-to-C₂H₄ 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-C₂H₄ in a MEA electrolyser. In the full SOEC-MEA cascade approach, we achieve CO₂-to-C₂H₄ with no loss of CO₂ to carbonate and a total energy requirement of ~138 GJ (ton C₂H₄)⁻¹, representing a ~48% reduction in energy intensity compared with the direct route.