were used as catalysts for cathode and anode, respectively. Titanium plate was used as current collector for both electrodes. An EPDM plate with the thickness of 1.5 mm was used as the chamber of electrolyte solution. The effective window for electrolysis was a circle with the diameter of 1.13 cm (area = 1 cm 2 ). Kapton tapes with circular windows with the same size was pasted on both electrodes to control the effective area exposed to the electrolyte. No membrane was used between cathode and anode and two electrodes shared the same electrolyte. CO2 and He streams were supplied behind cathode and anode, respectively. The volume of electrolyte solution was 10 mL, which was circulated with the flow rate of 1 mL/min. For each kind of electrolyte, chronopotentiometry test at 200 mA/cm 2 was conducted for 15000 seconds. No IR compensation was used when recording the cell voltage. The flow rates of CO2 and He were 100 sccm and 6 sccm, respectively. CO was detected by online GC analysis. The Linear sweeping voltammetry curves were collected with a scan rate of 5 mV/s. The resistance of electrolyte was determined by high-frequency impedance measurements and IR compensation was done after experiment.