The electrochemical reactions highly rely on the chemical environments, however, this phenomenon remains poorly understood in nonaqueous electrolyte. Herein, we study the effect of the electrode chemical environments on the electrochemical reduction of CO2 in molten carbonate. Using a Cu foam electrode, an acidic (CO2-rich) environment is created to achieve the efficient direct reduction of CO2 rather than the indirect reduction of CO32–. The acidic environment promotes a selective CO production thermodynamically, achieving a high CO current efficiency of 99 % at a current density of 779–1039 mA cm−2 at 700 °C. The Cu foam electrode works stably over 100 h at 260 mA cm−2 with an overpotential of 304 mV. This work reveals the role of the local chemical environment at the electrode/molten salt interface in governing the product selectivity and energy consumption, which is helpful for designing efficient high-temperature CO2 electrolyzers.