Improvement of desalination efficiency in capacitive deionization using a carbon electrode coated with an ion-exchange polymer

A composite carbon electrode coated with a cation-exchange polymer, crosslinked poly(vinyl alcohol) with sulfosuccinic acid, was fabricated to enhance the desalination performance of a capacitive deionization (CDI) system. The electrochemical properties of the prepared electrode were characterized by impedance spectroscopy, and desalination experiments were carried out at various operating conditions using a CDI cell with carbon electrodes only, and a membrane-capacitive-deionization (MCDI) cell including a coated-carbon electrode, to evaluate the effect of the coated-carbon electrode on desalination performance. The electrical resistance of the coated electrode was increased by a small amount over the uncoated electrode, but the capacitance was improved by the coating. In the CDI cell, the salt-removal efficiencies were in the range of 50–67%, while the efficiencies increased to 75–85% for the MCDI cell. Depending on the operating conditions, the salt-removal and current efficiencies of the MCDI cell were enhanced by 27–56% and 69–95%, respectively, compared to the CDI cell. The enhanced efficiency for the MCDI cell was attributed to the selective transport of cations between the electrode surface and bulk solution due to the cation-exchange coating layer.