**2.3 Electrochemical characterizations**

Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were operated on Chenhua® CHI600 electrochemical workstation. These measurements used a traditional three-electrode system, its working electrode was a 5-mm-diameter glassy carbon electrode, a platinum electrode was used as counter electrode, and the reference electrode was a saturated calomel electrode together with a salt bridge which was filled with the saturated potassium chloride solution. Before each test, polish the glassy carbon electrode on the deerskin with the 0.2-mm aluminum powder, then place the polished electrode in deionized water, and clean it with ultrasonic waves. The CV scan was performed in the range of −0.7–0.9 V for the electrolyte in the case of with and without CO2. Before the measurement, purge the electrolyte with nitrogen for 15 minutes in order to remove oxygen which dissolved

in the electrolyte. The CVs were measured at 25, 35, and 45°C, respectively, and at each temperature the CV was tested three times. Simultaneously, in the electrochemical impedance spectroscopy measurements, the sinusoidal excitation voltage suitable for the cells was 5 mV. The frequency was in the range of 0.01 Hz–100 kHz. The potential was settled at 0.15 V in order to ensure similar polarization.
