Selective Ion Transport Regulation Enables High Current Density CO ₂ ‐to‐C ₂₊ Conversion in Acid

Abstract Electrochemical carbon dioxide reduction reaction (CO 2 RR) under acidic condition offers great promise to achieve carbon‐efficient CO 2 electrolysis. However, acidic CO 2 RR has been hindered by the severe competing hydrogen evolution reaction (HER) and sluggish carbon–carbon coupling efficiency. Herein, an ion‐transport regulation strategy has been developed to customize the microenvironment near cathode surface during high current density electrolysis in acidic electrolyte. A hybrid adlayer composed of (010) planes‐enclosed ZrO 2 nanosheets and Nafion preferentially allows K + transport toward cathode through proton trapping and Donnan effect, thus simultaneously enriching K + and raising pH near cathode surface during CO 2 RR. Such K + ‐rich and alkaline microenvironment suppresses HER and favors C 2+ products formation. Particularly, a remarkable C 2+ Faraday efficiency (FE) of nearly 81% has been achieved with a partial current density of 484 mA cm −2 for C 2+ products on modified Cu electrode. This work demonstrates an effective strategy to boost the CO 2 RR performance in acidic electrolyzers for efficient and sustainable CO 2 conversion.