Copper nanoparticle ensembles for selective electroreduction of CO2 to C2–C3 products

Significance Electrochemical conversion of CO2 to carbon-based products, which can be used directly as fuels or indirectly as fuel precursors, is suggested as one of the promising solutions for sustainability. Not only does this process allow using renewables such as solar electricity as energy input, but CO2 emitted from the consumption process can be recycled back into fuels. The success of this technology depends on the value added to the product that forms from CO2, and therefore it is important to facilitate multicarbon product generation. This work presents a copper-based catalyst, formed in situ from an ensemble of nanoparticles, that is able to selectively generate C2–C3 products at low overpotentials with good stability, where their efficient formation has been difficult to achieve. 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.