(71b) Speeding up Electrochemical Separations with Energy Impunity Using Ionomer Binder Resin-Wafers

Authors: 
Arges, C. G., Louisiana State University
Lin, Y. J., Argonne National Laboratory
Valentino, L., Argonne National Laboratory
Palakkal, V. M., Louisiana State University
Lei, Q., Lousiana State University
Jordan, M., Louisiana State University
Resin wafer electrodeionization (RW-EDI) is an ionic separations technology implemented for various applications that includes ultrapure water production and remediating industrial process waste streams. The process works on the principle of using an applied electric field across two electrodes that are separated by a stack of alternating concentrated and dilute liquid compartments partitioned by ion-exchange membranes. At the heart of RW-EDI, the dilute liquid chamber features a porous resin wafer bed that augments the chamber’s ionic conductivity overcoming large electrical resistances that hinder energy efficiency. Current resin wafer materials feature a non-conductive polyethylene binder that immobilizes anion-exchange and cation-exchange resins.

This talk will present a new class of resin wafer materials featuring an ion conducing polymer binder. These ionomer binders are similar to the membrane chemistries used in proton exchange and anion exchange membrane fuel cells. The ionomer binder substantially enhances the resin wafer’s ionic conductivity by a factor of 3 to 6 for dilute NaCl solutions while also maintaining porosity for liquid flow. As a result, the ionomer-based resin wafers were shown to remove ions from liquid streams faster and with less energy. Inspection of the macrostructure of the resin wafer by electron microscopy and x-ray tomography revealed that the ionomer binder is a better utilized for adhering particles together when compared to polyethylene (i.e., the ionomer binder doesn’t cover the particles’ surfaces completely). Additionally, water-splitting measurements have been carried out in the resin wafers using a homemade 4-point electrochemical cell. Water-splitting occurs in resin wafers when anion-exchange and cation-exchange resin particles come in close proximity to each other leading to an abrupt bipolar junction region. The water-splitting forms hydronium and hydroxide ion carriers that supplement the ionic conductivity and regenerate the ion-exchange resin particles. Compared to bipolar membranes, water splitting in the resin wafer is quite poor when compared to bipolar membranes. The poor water splitting is attributed to the resin-wafer not containing a water dissociation catalyst and having a poor bipolar junction interface. These insights provide new directions for the design of resin wafers that are effective at splitting water.