Engineering the Local Microenvironment on Cu ₂ O with CTAB to Suppress Hydrogen Evolution and Promote C–C Coupling in CO ₂ Electroreduction

Electrochemical CO₂ reduction reaction (CO₂RR) to C₂₊ products is limited by the competing hydrogen evolution reaction (HER), particularly at industrially high current densities. Herein, we show that modifying cuprous oxide (Cu₂O) with the cationic surfactant cetyltrimethylammonium bromide (CTAB) efficiently mitigates this issue, achieving a C₂₊ Faradaic efficiency (FE) of 63% and a partial current density (<i>j</i>_C2+) of -244 mA cm^-2 at -1.776 V vs RHE, with the FE of H₂ suppressed to ∼10% over a wide potential window and an impressive 11-h stability. This performance represents a 2-fold increase in selectivity and a 2.5-fold increase in partial current density compared to unmodified Cu₂O under identical conditions. Our mechanistic investigations, including inductively coupled plasma mass spectrometry (ICP-MS), CO-adsorption measurements, <i>in situ</i> Raman spectroscopy, cyclic voltammetry, etc., reveal that CTAB integrates into both the surface and the bulk of the catalyst, concurrently limiting proton availability and stabilizing key *CO intermediates. We postulate that the enhanced selectivity toward C₂₊ products is attributed to the strengthened *CO adsorption on the catalyst and increased surface hydrophobicity, which collectively facilitate the dimerization of adsorbed *CO intermediates while suppressing HER.