The existing Cu-based electrocatalysts for electrochemical reduction of CO2 to chemical commodities suffer instability and large reaction overpotentials. Here we report a novel Cu nanoflower (NF) catalyst with a unique 3D chrysanthemum-like structure. Derived from CuO NFs, the Cu NFs were found to efficiently catalyze the CO2 reduction with 400 mV lower overpotential than polycrystalline Cu. Besides, H-2 production was suppressed to be below 25% in terms of Faradaic efficiency in a wide potential window, implying an excellent catalytic selectivity. Prolonged electrolysis showed that the Cu NFs kept a high catalytic activity towards CO2 reduction for over 9 h. In addition, for the first time, the deposition of amorphous carbon on the electrodes after catalysis was directly observed in this study. The reaction pathways of electrocatalytic CO2 reduction and the involvement of the surface carbon in this process were elucidated. (C) 2014 Elsevier Ltd. All rights reserved.