Carbon‐Efficient CO₂ Electrolysis to Ethylene with Nanoporous Hydrophobic Copper

Electrochemical carbon dioxide (CO 2 ) reduction offers a low‐carbon route to ethylene, when powered from renewable energy. Yet, the best‐performing CO 2 electrolysis systems employ neutral or alkaline electrolytes, resulting in low conversion efficiencies, which increases downstream separation costs. High conversion rates can be achieved with acidic electrolytes, albeit at the cost ethylene faradaic efficiency (FE < 45%). As a result, achieving high ethylene selectivity simultaneously with high conversion efficiency is an unmet challenge. Here, a 3D‐nanoporous catalyst is designed to modulate water and CO 2 concentration at the catalyst surface, reaching higher ethylene selectivity in a forward‐bias bipolar MEA that recovers unreacted CO 2 . An ethylene FE of 63% at 150 mA cm −2 is reported, and by optimizing for conversion efficiency, an ethylene FE of 58% along with an overall conversion efficiency of 82% is achieved. Stable performance for > 65 h at industrial current densities combined with a high ethylene concentration in the product stream showcases promising industrial viability.