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.