Tuning Cu Nanocluster Size for Methane Production in a Bipolar Membrane CO2 Electrolyzer

Abstract

The acidic electrochemical CO₂ reduction reaction (CO₂RR) offer potential for enhanced carbon utilization efficiency in hydrocarbon production, but its selectivity is constrained by the competing hydrogen evolution reaction (HER) and the poor C₂/C₁ product control. Herein, we demonstrate that precise tailoring of copper nanoclusters enables exceptional HER suppression while promoting selective CO₂-to-CH₄ conversion under acidic conditions (pH 2). Cu₃₆ nanoclusters achieve superior methane selectivity across a wide current density range (300–700 mA cm^–2), achieving a CH₄ partial current density (j_CH4) of 288 mA cm^–2. By analyzing the correlation between post-activation CO₂RR performance and crystal structure, we reveal that the structural evolution of Cu nanoclusters significantly influences their product distribution under electrochemical conditions, and confirm that ligands stabilize the Cu₃₆ cluster to avoid significant aggregation. Ligand-stabilized Cu exhibits enhanced stability in acidic media, maintaining operation for 70 h at 300 mA cm^–2. Our approach addresses key acidic CO₂RR challenges by simultaneously delivering high selectivity, activity, and stability─critical metrics for practical electrochemical carbon conversion.