Electrocatalytic conversion of CO2 to valuable chemicals is a highly promising route to close the carbon cycle. Herein, Zn catalysts derived from electrochemical reconstruction of ZnO materials are presented as efficient CO2-to-CO catalysts. We found that ZnO precursors with different morphologies (nanowires, nanoflowers, and nanoparticles) underwent deep electro-reconstruction and formed porous structures composed of hexagonal Zn crystals, regardless of their initial properties. Using ex-situ and in operando techniques, we revealed that metallic Zn is the active phase for CO2-to-CO. Because of the large surface area and stable crystal structure resulted from the reconstruction, ZnO-derived catalysts are highly selective and stable, showing >90% selectivity to CO and more than 18 h stability. The great potential of ZnO-derived catalysts for industrial applications was demonstrated in a flow reactor, where 91.6% Faradaic efficiency for CO at a current density of 200 mA cm−2 can be achieved at –0.62 V vs. RHE.