Acidic CO₂ electroreduction (CO₂R) offers a promising pathway for efficient liquid chemical production using renewable energy. However, the competing hydrogen evolution reaction (HER) hinders selectivity and energy efficiency, especially at high current densities. This study demonstrates that enhancing CO₂R intermediate coverage on catalysts improves CO₂R while suppressing HER. Robust Cu₆Sn₅ catalysts, engineered for strong OCHO affinity and weak H binding, achieved 91% Faradaic efficiency for formic acid (FA) at 1.2 A cm⁻² and pH 1, with a record 77.4% single-pass carbon efficiency at 0.5 A cm⁻² over 300 hours. In situ ATR-FTIR spectroscopy confirmed a 2.8x increase in OCHO coverage on Cu₆Sn₅ compared to Sn. A cation-free, solid-state-electrolyte MEA produced 0.36 M pure FA at 88% FE and 37% full-cell energy efficiency over 130 hours.

Xiaohan Yu, Yuting Xu, Le Li, Mingzhe Zhang, Wenhao Qin, Fanglin Che, Miao Zhong