Electroreduction of Carbon Dioxide into Selective Hydrocarbons at Low Overpotential Using Isomorphic Atomic Substitution in Copper Oxide

The conversion of carbon dioxide into selective hydrocarbons is vital for green energy generation. Due to the chemical instability and lower activity, environmentally stable transition metal oxides (e.g., CuO) are unpopular for CO₂ electroreduction catalysis. Here, we demonstrate substitution of Cu with an isomorphic atom, i.e., Ni, in CuO and utilize it for improving the hydrocarbon selectivity by 4 times as compared to that of pristine CuO. Hydrocarbon formation is achieved at the lowest possible applied potential (-0.2 V, reversible hydrogen electrode). This gives the overpotential of about 0.37 V for methane and 0.28 V for ethylene, the lowest ever reported. Employing the ionic interaction between Ni and Cu, this catalyst suppresses the hydrogen evolution reaction to improve the hydrocarbon selectivity prominently. It is observed that current normalized by the Brunauer-Emmett-Teller surface area gives 15-20 times enhancement in the case of Ni-substituted CuO compared to undoped CuO. The in situ experiments indicate that Ni-doped CuO prefers CO pathways compared to formate, resulting into high hydrocarbon selectivity. The experimental observation is further supported by density functional theory studies, which reveal that the Ni-doped CuO catalyst has a higher limiting potential for CO₂ electroreduction to CH₄ due to the stabilization of the CH₂O intermediate on the Cu_0.9375Ni_0.0625O surface rather than the CHO intermediate, in comparison to the pristine CuO surface.