UC Berkeley

Direct conversion of carbon dioxide to multicarbon products remains as a grand challenge in electrochemical CO₂ reduction. Various forms of oxidized copper have been demonstrated as electrocatalysts that still require large overpotentials. Here, we show that an ensemble of Cu nanoparticles (NPs) enables selective formation of C₂-C₃ products at low overpotentials. Densely packed Cu NP ensembles underwent structural transformation during electrolysis into electrocatalytically active cube-like particles intermixed with smaller nanoparticles. Ethylene, ethanol, and n-propanol are the major C₂-C₃ products with onset potential at -0.53 V (vs. reversible hydrogen electrode, RHE) and C₂-C₃ faradaic efficiency (FE) reaching 50% at only -0.75 V. Thus, the catalyst exhibits selective generation of C₂-C₃ hydrocarbons and oxygenates at considerably lowered overpotentials in neutral pH aqueous media. In addition, this approach suggests new opportunities in realizing multicarbon product formation from CO₂, where the majority of efforts has been to use oxidized copper-based materials. Robust catalytic performance is demonstrated by 10 h of stable operation with C₂-C₃ current density 10 mA/cm² (at -0.75 V), rendering it attractive for solar-to-fuel applications. Tafel analysis suggests reductive CO coupling as a rate determining step for C₂ products, while n-propanol (C₃) production seems to have a discrete pathway.