Influence of Metal Oxide Coatings, Carbon Materials and Potentials on Ion Removal in Capacitive Deionization

Abstract

© 2018 The Electrochemical Society. Metal oxide coated carbon materials were shown to have increased ion removal over many of the uncoated carbons when used in capacitive deionization; however, the influence of the coating was dependent on the carbon material used as the substrate. Specifically, four different carbon materials, coated and uncoated, were tested. During removal, the negative electrode was coated with SiO 2 and the positive with γ-Al 2 O 3 . The SiO 2 coatings improved Ca 2+ removal for 3 of the 4 carbon materials tested and the γ-Al 2 O 3 coatings improved Cl− removal for 2. The mechanism for this increase in removal appeared to be carbon dependent, and could be associated with the addition of new surface groups, improved wettability, or for the low surface area carbon, an increase in specific surface area of the composite material. Moreover, it was also shown that the surface area of the carbon material was not the only factor that determined the electrosorption capacities of the electrode. In addition, certain electrodes had large improvements in ion removal with increases in the applied potential. However, the stability of the electrodes, as well as faradaic reactions that may evolve at high potentials, must be considered when increasing the potential to improve ion removal.