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 C-2 products, ethylene and ethane, as well as to the fully reduced C-1 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 C-2 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 C-2 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 C-2 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 (CO2)-C-13 confirmed that the detected products were produced exclusively by the reduction of CO2.