The maximum allowable charge for operating membrane capacitive deionization without electrode reactions

We have studied a new method to operate a membrane capacitive deionization (MCDI) without electrode reactions by controlling the total charge (TC) supplied to the MCDI cell. The MCDI experiments were carried out by varying the TC (45-90 C/g) at a high cell potential. When approximately 59 C/g of charge was supplied to the carbon electrode, the electrode reaction began. Thus the MAC value, which is the maximum charge supplied to the carbon electrode at the point where the electrode reactions begin, was determined to be 59 C/g. The carbon oxidation reaction occurred when 59-83 C/g of charge was supplied. At 83 C/g or more, the water oxidation reaction proceeded at a rapid rate, resulting in a drastic decrease in the charge efficiency. No electrode reactions were found during the MCDI operation at a TC value lower than the MAC value. When the MCDI system was operated at a TC higher than the MAC, however, the effluent pH and concentration changed as the adsorption and desorption process was repeated, resulting in deterioration of the desalination performance. It was verified that the electrode reactions can be easily controlled by adjusting the TC supplied to the MCDI cell.