Inspired by grain refinement in the traditional metal processing, we develop a top-down approach by facile multiple-redox treatment to obtain the downsized Cu crystals over the self-supported copper electrodes for the enhanced selective CO2 electroreduction. Specifically, the treated copper meshes exhibit an increased activity and selectivity for CO production with high Faradaic efficiency of 78% and partial current density of 13.2 mA cm(-2) at the potential of -0.8 V (vs. RHE). This investigation intends to ascribe the enhanced properties to the surface downsized crystals of Cu electrode induced by the multiple-redox treatments. Moreover, the molecular reaction mechanism of the elementary reaction of CO2 conversion to CO is also discussed. This work offers a new top-down strategy to design and preparation of nanosized catalytic catalysts on a self-supported electrode and valuable insights in selective CO2 conversion toward valuable fuels over Cu-based electrodes. (C) 2019 Elsevier Inc. All rights reserved.