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 .