The KHCO3 or K2SO4 solutions that had been pre-saturated with CO2 or N2 were introduced into the electrochemical cell at a flow rate of 10 µL/min to minimize the time it took to exchange CuSO4 to KHCO3 or K2SO4 in the electrochemical cell. Once the pre-saturated KHCO3 or K2SO4 electrolyte reached the cell, the CO2 ER protocol was initiated by fixing EWE at the desired value. EWE was maintained constant during the entire experiment.