Switching CO2 electroreduction on copper between C2 products and HCOOH by ionic surfactants

Abstract

Electrochemical CO₂ reduction (CO₂RR) represents a promising route to sustainable fuels and chemicals, yet controlling product selectivity remains challenging. Here, we demonstrate that ionic surfactants added to the electrolyte can effectively modulate the interfacial microenvironment and direct the reaction pathway on copper catalysts. By introducing anionic sodium hexadecyl sulfate (SDS₁₆) or cationic cetyltrimethylammonium bromide (CTAB), we achieve high selectivity toward C₂ products (Faradaic efficiency of 70.1%) or formate (HCOOH) (FE of 71.31%), respectively. In situ Raman spectroscopy reveals that SDS₁₆ enhances *CO adsorption and restructures interfacial water to promote C–C coupling, whereas CTAB facilitates *OCHO desorption toward formate. Molecular dynamics simulations (MD) and density functional theory calculations (DFT) further elucidate that the two surfactants adopt distinct adsorption configurations on Cu, with CTAB stabilizing key intermediates via hydrogen bonding. This work provides a versatile electrolyte-engineering strategy for precisely controlling CO₂RR selectivity through interfacial hydrophobicity tuning.