Facile Synthesis of Sub‐Nanometric Copper Clusters by Double Confinement Enables Selective Reduction of Carbon Dioxide to Methane

Previous density‐functional theory (DFT) calculations show that sub‐nanometric Cu clusters (i.e., 13 atoms) favorably generate CH 4 from the CO 2 reduction reaction (CO 2 RR), but experimental evidence is lacking. Herein, a facile impregnation‐calcination route towards Cu clusters, having a diameter of about 1.0 nm with about 10 atoms, was developed by double confinement of carbon defects and micropores. These Cu clusters enable high selectivity for the CO 2 RR with a maximum Faraday efficiency of 81.7 % for CH 4 . Calculations and experimental results show that the Cu clusters enhance the adsorption of *H and *CO intermediates, thus promoting generation of CH 4 rather than H 2 and CO. The strong interactions between the Cu clusters and defective carbon optimize the electronic structure of the Cu clusters for selectivity and stability towards generation of CH 4 . Provided here is the first experimental evidence that sub‐nanometric Cu clusters facilitate the production of CH 4 from the CO 2 RR.