Membrane Capacitive Deionization (MCDI) is a low-cost desalination technology that utilizes ion-exchange polymer coated electrodes to reversibly adsorb and desorb ions. Ion-exchange membranes serve to improve charge efficiency by excluding co-ions near the surface of the electrode. Modification of the ion-exchange coatings provide opportunities to improve energy efficiency, capacities, and incorporate selectivity towards ions and contaminants of interest. Here, we report the design, fabrication, and testing of high capacity ion-exchange polymer coated electrodes for MCDI. Electrodes are first prepared by flow coating an aqueous slurry of activated carbon, water-soluble polymer, and crosslinker. After annealing and crosslinking, electrodes are subsequently flow-coated with a thin layer of cation- or anion-exchange polymer. Ion-exchange coatings based on modified polyvinyl alcohol produce salt adsorption capacities in excess of 15 mg/g and overall charge efficiencies higher than 98%. Partially sulfonated pentablock copolymer (sPBC) can serve as an effective anion-exchange coating for MCDI and produce charge efficiencies up to 85%. The performance of block copolymer coatings is strongly dependent on ion-exchange capacity and processing conditions, specifically the polarity of the casting solvent. We correlate changes in performance with morphological changes in the self-assembled ion-exchange layer and achieve optimal performance for inverted micellar morphology of the ion-exchange layer. Finally, we demonstrate an approach to achieve selective uptake of divalent ions through functionalization of the ion-exchange coating layer or deposition of crosslinked ion-exchange particles. The selective MCDI process demonstrated can uptake Ca2+ over Na+ with a selectivity of 10:1 and SO4- over Cl- with a selectivity of 4:1. This work demonstrates advances in the design of ion-exchange polymer coatings for capacitive deionization.

Functionalized and self-assembled ion exchange coatings for capacitive deionization

2019 Spring National Meeting

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