Novel hierarchical copper oxide (CuXO) nanosphere particles are synthesized, and then coated onto gas diffusion layer (carbon) to form a working electrode for catalyzing CO2 electroreduction. When applying a negative voltage to the working electrode, the metal Cu nanoparticles which are induced by the CuXO nanospheres appear. CuXO and metal Cu together form the CuXO/Cu nanocatalysts which show high catalytic activity for CO2 electroreduction. The morphology, composition, crystal structure and surface area of the CuXO/Cu electrocatalysts are characterized using scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The CuXO/Cu nanoparticles are tested as the catalysts for CO2 electroreduction using cyclic voltammetry and linear sweep voltammetry in CO2-saturated 0.5 M KHCO3 aqueous electrolyte. It is found that the CO2 electroreduction activity is highly improved using this CuXO/Cu nanocatalyst, which remains stable during 20 h of electrolysis, along with the high selectivity with a similar to 62% of Faradaic efficiency for formate production. Detailed kinetic information relevant to the catalysis is also discussed. (C) 2014 Published by Elsevier Ltd.