Among all CO2 electroreduction products, methane (CH4) and ethylene (C2H4) are two typical and valuable hydrocarbon products which are formed in two different pathways: hydrogenation and dimerization reactions of the same CO intermediate. Theoretical studies show that the adsorption configurations of CO intermediate determine the reaction pathways towards CH4/C2H4. However, it is challenging to experimentally control the CO adsorption configurations at the catalyst surface, and thus the hydrocarbon selectivity is still limited. Herein, we seek to synthesize two well-defined copper nanocatalysts with controllable surface structures. The two model catalysts exhibit a high hydrocarbon selectivity toward either CH4 (83%) or C2H4 (93%) under identical reduction conditions. Scanning transmission electron microscopy and X-ray absorption spectroscopy characterizations reveal the low-coordination Cu-0 sites and local Cu-0/Cu+ sites of the two catalysts, respectively. CO-temperature programed desorption, in-situ attenuated total reflection Fourier transform infrared spectroscopy and density functional theory studies unveil that the bridge-adsorbed CO (COB) on the low-coordination Cu-0 sites is apt to be hydrogenated to CH4, whereas the bridge-adsorbed CO plus linear-adsorbed CO (COB + COL) on the local Cu-0/Cu+ sites are apt to be coupled to C2H4. Our findings pave a new way to design catalysts with controllable CO adsorption configurations for high hydrocarbon product selectivity. (C) 2020 Science China Press. Published by Elsevier B.V. and Science China Press. All rights reserved.