Electrochemical Carbon Dioxide Reduction to Hydrocarbons with a Nickel-Gallium Thin Film Catalyst at Low Overpotentials

We present bimetallic Ni-Ga thin films as new electro-catalysts for the conversion of carbon dioxide into methane, ethylene and ethane at low overpotentials in aqueous media. Three different phases of Ni-Ga (NiGa, Ni 3 Ga and Ni 5 Ga 3 ) were prepared by drop casting, and tested for CO 2 reduction activity in aqueous carbonate electrolytes acidified to pH 6.8 with 1 atm CO 2 . CH 4 , C 2 H 4 and C 2 H 6 are detected at potentials as anodic as -0.48V vs RHE, representing some of the lowest onset potentials for C 2 -product formation reported to date. Carbon monoxide reduction over the Ni-Ga thin films also resulted in the formation of CH 4 , C 2 H 4 and C 2 H 6 with similar Faradaic efficiencies, consistent with a CO 2 reduction mechanism that involves a CO intermediate. Theoretically, hydrocarbon formation over single element transition metal surfaces is governed by scaling relations, where the binding energy of intermediates like adsorbed CO and adsorbed CHO are coupled. This coupling typically manifests experimentally in high overpotentials for CO 2 reduction on the transition metals. The low overpotentials we observe for CO 2 reduction on the bimetallic Ni-Ga are suggested to arise from the material not being governed by such scaling relations.