The fcc/hcp (face centered cubic/hexagonal close-packed) noble metal nanomaterials have demonstrated excellent catalytic performance towards hydrogen evolution reaction and CO₂ reduction reaction. Among all the monometallic catalysts, copper has drawn great attention because of its unique ability to convert CO₂ into hydrocarbon products with an appreciable selectivity. However, the wet-chemistry synthesis of fcc/hcp Cu heterophase nanostructures still remains a great challenge. Herein, we reported a high temperature solution reduction method to synthesize heterophase Cu nanosheets with a thickness of 28 nm and a diameter of 85.6 nm. The heterophase Cu nanosheets exhibited high selectivity towards CO₂ reduction reaction and high faradaic efficiency for methane production (60.2%) at -1.25 V vs RHE. Atomic-level structural investigation revealed the existence of side surface fcc/2H and fcc/4H heterophase (face centered cubic; 2H: hexagonal close-packed with stacking sequence of “BC”; 4H: hexagonal close-packed with stacking sequence of “ACB”). First-principles calculations suggest that the existence of fcc/2H and fcc/4H heterophase interface possess lower ΔG_*CHO compared to a fcc Cu surface, indicating a lower kinetic barrier for CO₂ reduction reaction.