Cu(OH)₂/CuO nanocomposite-derived Cu₂O/Cu was highly efficient for CO₂ electroreduction to C2 products. The highest faradaic efficiency and current density could reach 64.5% and 26.2 mA cm⁻², respectively. By changing the calcination time, moderate grain boundary density and the Cu⁺/Cu⁰ ratio in catalysts can be controlled, leading to a large number of active sites and low interfacial charge transfer resistance.