Abstract: Electrochemical CO₂ reduction (CO₂) 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 CO₂R at low pH. Herein we report an alternative approach to selective CO₂R (>70 % Faradaic efficiency for C2+ products, FEC2+) at low pH (pH=2; H3PO4/KH2PO4) 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 H3PO4 (pH≈1) at low [K+] (0.1 M), even at low operating current, conditions where HER can otherwise dominate.
