Electrodialysis is an industrial-scale technique used to purify water. Here the application of a DC electric field drives dissolved ions across ion-selective membranes to decrease the salt concentration and create a purified water stream. Due to the large electricity costs for operating such a facility, only a fraction of water purification plants are based on electrodialysis techniques, with the majority employing reverse osmosis. One of the key factors influencing the cost of electrodialysis is the conductivity of the ion-selective membranes. Here we present recent results from studies leveraging layer by layer (LbL) deposition of polyelectrolytes of poly(ethyleneimine) and poly(acrylic acid) onto nanoporous polymer support layers in order to increase their ionic conductivity and ionic selectivity. Use of crosslinking agents creates mechanically stable polyelectrolyte films on and in the nanopores, though choice of various crosslinking agents is shown to either enhance or hinder ionic selectivity. Variation of LbL polyelectrolyte deposition parameters and starting nanoporous supporting polymer support is demonstrated to control the ionic selectivity and conductivity, adhesion, and durability of the coated membranes. The performance of these membranes is compared to commercial electrodialysis membranes using a small-scale electrodialysis test bed.
Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.