Zn-CO batteries are excellent candidates for both electrical energy output and CO utilization, whereas the main challenge is to design electrocatalysts for electrocatalytic CO reduction reactions with high selectivity and low cost. Herein, the three-phase heterojunction Cu-based electrocatalyst (Cu/CuO-SbO-15) is synthesized and evaluated for highly selective CO reduction to CO, which shows the highest faradaic efficiency of 96.3% at -1.3 V versus reversible hydrogen electrode, exceeding the previously reported best values for Cu-based materials. In situ spectroscopy and theoretical analysis indicate that the Sb incorporation into the three-phase heterojunction Cu/CuO-SbO-15 nanomaterial promotes the formation of key COOH intermediates compared with the normal Cu/CuO composites. Furthermore, the rechargeable aqueous Zn-CO battery assembled with Cu/CuO-SbO-15 as the cathode harvests a peak power density of 3.01 mW cm as well as outstanding cycling stability of 417 cycles. This research provides fresh perspectives for designing advanced cathodic electrocatalysts for rechargeable Zn-CO batteries with high-efficient electricity output together with CO utilization.