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

Electrochemical CO 2 reduction reaction (CO 2 RR) to C 2+ products is limited by the competing hydrogen evolution reaction (HER), particularly at industrially high current densities. Herein, we show that modifying cuprous oxide (Cu 2 O) with the cationic surfactant cetyltrimethylammonium bromide (CTAB) efficiently mitigates this issue, achieving a C 2+ Faradaic efficiency (FE) of 63% and a partial current density ( j C2+ ) of −244 mA cm –2 at −1.776 V vs RHE, with the FE of H 2 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 Cu 2 O under identical conditions. Our mechanistic investigations, including inductively coupled plasma mass spectrometry (ICP-MS), CO-adsorption measurements, in situ 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 C 2+ 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.