Stabilizing Cu2+ Ions by Solid Solutions to Promote CO2 Electroreduction to Methane.

Copper is the only metal catalyst that can perform the electrocatalytic CO2 reduction reaction (CRR) to produce hydrocarbons and oxygenates. Its surface oxidation state determines the reaction pathway to various products. However, under the cathodic potential of CRR conditions, the chemical composition of most Cu-based catalysts inevitably undergoes electroreduction from Cu2+ to Cu0 or Cu1+ species, which is generally coupled with phase reconstruction and the formation of new active sites. Since the initial Cu2+ active sites are hard to retain, there have been few studies about Cu2+ catalysts for CRR. Herein we propose a solid-solution strategy to stabilize Cu2+ ions by incorporating them into a CeO2 matrix, which works as a self-sacrificing ingredient to protect Cu2+ active species. In situ spectroscopic characterization and density functional theory calculations reveal that compared with the conventionally derived Cu catalysts with Cu0 or Cu1+ active sites, the Cu2+ species in the solid solution (Cu-Ce-Ox) can significantly strengthen adsorption of the *CO intermediate, facilitating its further hydrogenation to produce CH4 instead of dimerization to give C2 products. As a result, different from most of the other Cu-based catalysts, Cu-Ce-Ox delivered a high Faradaic efficiency of 67.8% for CH4 and a low value of 3.6% for C2H4.