Suppression of electrode reactions and enhancement of the desalination performance of capacitive deionization using a composite carbon electrode coated with an ion-exchange polymer

Abstract

The suppression of electrode reactions at the composite carbon electrode (IEP-CCE) coated with an ion-exchange polymer (IEP) was studied. IEP-CCEs coated with a cation- and anion-exchange polymer on a carbon electrode (CE) were prepared. To compare the electrode reactions of coated and uncoated CEs, a capacitive deionization cell using the IEP-CCEs and a membrane capacitive deionization (MCDI) cell using uncoated CEs were manufactured. For each cell, the maximum allowable charge (MAC), which is the charge accumulated at the start of the electrode reactions, was measured. The MAC values of the uncoated CE and IEP-CCE were 58.8 and 79.8 C/g, respectively. It is thought that the IEP coating suppresses carbon oxidation, resulting in an increase in the MAC. Desalination experiments were conducted while varying the total charge (TCAd) during the adsorption process. When the TCAd was above the MAC, electrode reactions occurred in both cells, but adsorption–desorption proceeded stably without reaction below the MAC. In this case, the amount of adsorption in the IEP-CCE cell was 20.3 mg/g, which was approximately 47% higher than that in the MCDI cell (13.8 mg/g). The results showed that the IEP-CCE is very effective in improving the adsorption performance by suppressing electrode reactions.