Modulation of Local Environment for Selective Bicarbonate Conversion to Multi‐Carbon Products

ABSTRACT Renewable electricity‐powered direct electrosynthesis of multi‐carbon (C 2+ ) products such as ethylene (C 2 H 4 ) from bicarbonate offers a sustainable route for carbon dioxide (CO 2 ) utilization but is hindered by limited CO 2 availability and unfavorable reaction environments. Existing approaches, such as electrolyte engineering and buffering layers, often improve selectivity at the cost of higher full‐cell voltages, creating a trade‐off between selectivity and energy efficiency. Here, we introduce a new electrode design for direct bicarbonate (HCO 3 − ) conversion using highly porous copper electrodes coated with an ionomer/carbon layer. Multiphysics modeling results reveal that increasing HCO 3 − concentration enhances local in situ‐generated CO 2 ( i ‐CO 2 ) availability but suppresses the alkaline microenvironment required for C‐C coupling. We found that partially coating a large‐pore Cu electrode with the ionomer/carbon layer addresses the limitation by fine‐tuning the local reaction environment to favor C 2+ products while maintaining high CO 2 availability for high reaction rates. The optimized electrode achieves a C 2 H 4 Faradaic efficiency (FE) of 43% (total C 2+ FE of 60%) at 150 mA/cm 2 , with a low full‐cell voltage of 3.38 V. When coupled to a dilute CO 2 source (20% in argon) and pulsed operation, the system sustains > 30% C 2 H 4 FE for ∼150 h at 150 mA/cm 2 .