Transformation of carbon dioxide to useful fuels or chemicals is desirable to build up a sustainable society. In this study, we demonstrate that Cu2S has great potential for electrochemical CO2 reduction. They enable the selective CO2 reduction to formate starting at a low overpotential (∼ 120 mV), with high current density (over -20 mA/cm2 at -0.89 VRHE), and good Faradaic efficiency (>75%) over a broad potential window (-0.7 VRHE to -0.9 VRHE). X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and in-situ Raman spectroscopy studies reveal that Cu2S catalysts are electrochemically stable under the reaction conditions. Further-more, Cu2S catalysts show excellent durability without deactivation following more than 15 cycles (1.0 h per cycle) of operation.