Scalable Synthesis of Chloride-Mediated Copper Nanocatalysts for Selective Ethylene Production in Large-Area CO2 Electrolyzers

Abstract

Copper-based electrocatalysts are essential for the electrochemical reduction of CO₂ to ethylene; however, preventing the rapid reduction of active Cu⁺ species and suppressing the competing hydrogen evolution reaction remain key challenges. Herein, we demonstrate that precursor engineering is a decisive strategy for modulating the electronic structure and catalytic selectivity of Cu nanoparticles (NPs). Using a scalable wet-chemical reduction method, we synthesized chloride-incorporated Cu NPs (Cu-Cl NPs) on a gram scale. In a large-area (25 cm²) membrane electrode assembly electrolyzer, the Cu-Cl NPs achieved a peak ethylene Faradaic efficiency of 31% at 400 mA cm⁻², markedly outperforming sulfate-derived counterparts. Operando X-ray absorption fine structure analysis and in situ Raman spectroscopy revealed that chloride dictates the unique surface reconstruction, maintaining the Cu⁰/Cu¹⁺ interface even at high current densities. These persistent Cl-stabilized Cu⁺ sites improved catalytic performance. This structural evolution steers the reaction pathway toward selective C₂H₄ formation by promoting C–C coupling over competing hydrogen evolution reaction, highlighting the overlooked potential of precursor anions as functional dopants and offering a facile route to design robust electrocatalysts for industrial-scale CO₂ valorization.