Nickel–Gallium-Catalyzed Electrochemical Reduction of CO2 to Highly Reduced Products at Low Overpotentials

We report the electrocatalytic reduction of CO₂ to the highly reduced C₂ products, ethylene and ethane, as well as to the fully reduced C₁ product, methane, on three different phases of nickel–gallium (NiGa, Ni₃Ga, and Ni₅Ga₃) films prepared by drop-casting. In aqueous bicarbonate electrolytes at neutral pH, the onset potential for methane, ethylene, and ethane production on all three phases was found to be −0. 48 V versus the reversible hydrogen electrode (RHE), among the lowest onset potentials reported to date for the production of C₂ products from CO₂. Similar product distributions and onset potentials were observed for all three nickel–gallium stoichiometries tested. The onset potential for the reduction of CO₂ to C₂ products at low current densities catalyzed by nickel–gallium was >250 mV more positive than that of polycrystalline copper, and approximately equal to that of single crystals of copper, which have some of the lowest overpotentials to date for the reduction of CO₂ to C₂ products and methane. The nickel–gallium films also reduced CO to ethylene, ethane, and methane, consistent with a CO₂ reduction mechanism that first involves the reduction of CO2 to CO. Isotopic labeling experiments with ^ (13) CO₂ confirmed that the detected products were produced exclusively by the reduction of CO₂.