Organic Additive‐derived Films on Cu Electrodes Promote Electrochemical CO₂ Reduction to C₂₊ Products Under Strongly Acidic Conditions

Electrochemical CO₂ reduction (CO₂ R) at low pH is desired for high CO₂ utilization; the competing hydrogen evolution reaction (HER) remains a challenge. High alkali cation concentration at a high operating current density has recently been used to promote electrochemical CO₂ R at low pH. Herein we report an alternative approach to selective CO₂ R (>70 % Faradaic efficiency for C₂₊ products, FEC2+ ) at low pH (pH 2; H₃ PO₄ /KH₂ PO₄ ) and low potassium concentration ([K⁺ ]=0.1 M) using organic film-modified polycrystalline copper (Modified-Cu). Such an electrode effectively mitigates HER due to attenuated proton transport. Modified-Cu still achieves high FEC2+ (45 % with Cu foil /55 % with Cu GDE) under 1.0 M H₃ PO₄ (pH≈1) at low [K⁺ ] (0.1 M), even at low operating current, conditions where HER can otherwise dominate.