Cascade CO₂ electroreduction enables efficient carbonate-free production of ethylene

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.