(401g) Development of Electrically Reversible Ion Exchange (ERIE) Electrodes for Desalination and Aqueous Deionization

Growing demand is straining existing supplies of fresh water, and more efficient and robust methods are needed for removal of mineral or ionic contaminants from other water sources. A new technology employing p-doped conducting polymer electrodes which reversibly electrosorb aqueous ionic contaminants when a small voltage is applied, and regenerate when the potential is removed or reversed has been developed and demonstrated. By electrodepositing doped polypyrrole (PPy) or poly(3,4) ethylenedioxythiophene (PEDOT) onto the porous carbon substrates, we create electrodes with both Faradaic (ion exchange) and non-Faradaic (electrical double layer) charging mechanisms (see Figure 1). Their performance was evaluated electrochemically via Dual Electrode Cyclic Voltametry (DECV) to discern the ion insertion and removal behavior, and via Cyclic Step Chronoamperometry (CSCA) to determine the specific ionic capacities, and the charge/discharge rates of the electrodes. The voltage requirement is only 1.0 and 1.5 volts, and an electrochemical efficiency of up to 90% is achievable. Batch and continuous ion absorption/desorption tests using both symmetric and asymmetric electrode pairs were conducted on saltwater and other aqueous ion solutions to confirm the ionic removal, electrode efficiency and cycling rates, and electrode durability during repeated cycling. These new electrode materials demonstrate ionic capacities (50 to over 100 milliequivalents/gram polymer) that are comparable to or better than ion exchange resins, and greater than the best current Capacitive DeIonization (CDI) electrodes. Our measurements indicate that the ERIE energy requirements are lower than existing CDI or reverse osmosis technologies and offers an attractive alternative for deionization of seawater or brackish waters, and to ion exchange resins for water softening or removal of harmful ionic contaminants.