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 CuOx particles, removing lithium oxides formed, and electrochemically reducing CuOx 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 angstrom allows a current density exceeding that of unmodified CuOx nanoparticles by about 12 folds and a Faradaic efficiency of approximate to 80% to C2+. Density functional theory calculations support that d(s) of 5-6 angstrom 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.