Surfactant Chain Length Driven Selectivity Switch between C ₁ and C ₂₊ Products in CO ₂ Electroreduction on Copper

Electrochemical CO 2 reduction (ECR) on copper offers a promising route to convert CO 2 into value-added chemicals, yet the product selectivity is difficult to control. Here, we develop a surfactant modification strategy to systematically tune the electrode/electrolyte interface using a series of alkyltrimethylammonium bromides (Cx-TAB, x = 4, 6, 8, 12, 16, and 18) on Cu 2 O-derived Cu electrodes. ECR performance shows a selectivity switch controlled by the surfactant chain length. The Faradaic efficiency (FE) of C 2+ products follows a volcano-type trend with an optimum at C8-TAB, increasing from 41.0% on unmodified Cu to 55.5% on C8-TAB-Cu, whereas the FE of C 1 products increases with chain length and reaches 78.6% for C18-TAB-Cu in comparison to 31.5% over Cu. In situ investigation and electrochemical analysis indicate that Cx-TAB functionalization accelerates interfacial kinetics of ECR and regulates interfacial hydration, which suppresses hydrogen evolution and shifts the key adsorbed intermediates, thus exhibiting the chain-length-dependent selectivity relationship.