Atomic‐Scale Spacing between Copper Facets for the Electrochemical Reduction of Carbon Dioxide

Copper (Cu) offers a means for producing value‐added fuels through the electrochemical reduction of carbon dioxide (CO₂), i.e., the CO₂ reduction reaction (CO₂RR), but designing Cu catalysts with significant Faradaic efficiency to C₂₊ products remains as a great challenge. This work demonstrates that the high activity and selectivity of Cu to C₂₊ products can be achieved by atomic‐scale spacings between two facets of Cu particles. These spacings are created by lithiating CuO_x particles, removing lithium oxides formed, and electrochemically reducing CuO_x to metallic Cu. Also, the range of spacing (d_s) is confirmed via the 3D tomographs using the Cs‐corrected scanning transmission electron microscopy (3D tomo‐STEM), and the operando X‐ray absorption spectra show that oxidized Cu reduces to the metallic state during the CO₂RR. Moreover, control of d_s to 5–6 Å allows a current density exceeding that of unmodified CuO_x nanoparticles by about 12 folds and a Faradaic efficiency of ≈80% to C₂₊. Density functional theory calculations support that d_s of 5–6 Å maximizes the binding energies of CO₂ reduction intermediates and promotes C–C coupling reactions. Consequently, this study suggests that control of d_s can be used to realize the high activity and C₂₊ product selectivity for the CO₂RR.