Highly Tension-Strained Copper Concentrates Diluted Cations for Selective Proton-Exchange Membrane CO₂ Electrolysis

Electrolysis of carbon dioxide (CO₂) in acid offers a promising route to overcome CO₂ loss in alkaline and neutral electrolytes, but requires concentrated alkali cations (typical ≥3 M) to mitigate the trade-off between low pH and high hydrogen evolution reaction (HER) rate, causing salt precipitation. Here we report a strategy to resolve this problem by introducing tensile strain in a copper (Cu) catalyst, which can selectively reduce CO₂ to valuable multicarbon products, particularly ethylene, in a pH 1 electrolyte with 1 M potassium ions. We find that the tension-strained Cu creates an electron-rich surface that concentrates diluted potassium ions, contributing to CO₂ activation and HER suppression. With this catalyst, we show constant ethylene Faradaic efficiency (FE) of 44.3 % over 100 hours at 400 mA cm^-2 and a cell voltage of 3.1 volts in a proton-exchange membrane electrolyser. Moreover, selective electrosynthesis of ethylene oxide using the as-produced ethylene was demonstrated in an integrated system.