Membrane Capacitive Deionization (MCDI) is a low-cost desalination technology that utilizes ion-exchange polymer coated electrodes to reversibly adsorb and desorb ions. MCDI outperforms reverse osmosis and conventional desalination methods in energy efficiency, but only at low salinities due to a limited ion uptake capacity of electrodes. MCDI electrodes are also typically prepared using organic polymers and solvents, and a fully aqueous processing and fabrication route would be desirable. Here, we report a scalable, aqueous processing approach to prepare 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. These electrodes exhibit salt adsorption capacities in excess of 15 mg/g and overall charge efficiencies higher than 98%, much higher than typically achieved for activated carbon electrodes with organic polymer binders. We attribute the increased capacity and charge efficiency to the use of a hydrophilic polymer binder and ion exchange polymer coating respectively, and our overall approach demonstrates a simple, environmentally friendly, and cost-effective method for high capacity MCDI systems. We furthermore 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.

Ion-selective and high capacity electrodes for membrane capacitive deionization

255th National Meeting (2018)

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