MCDI, an electrochemical technology, offers the enticing prospect of low energy water desalination as it can recover energy (demonstrated up to 83%)2 when discharging the saturated electrodes as a supercapacitor. Most research today has focused on porous carbon electrodes to increase MCDI capacity. However, material innovation with regard to the ion-exchange membranes used in MCDI has been neglected. Today’s MCDI currently uses electrodialysis (ED) membranes – not originally designed for MCDI. The ion-exchange membranes for ED tend to be thick as they serve as a separator in addition to an ion-conducting electrolyte in electrodialysis. In MCDI, the ion-exchange membranes do not serve as separator and they are employed to prevent co-ion adsorption to the porous carbon electrodes.
This talk will demonstrate how thinner ion-exchange membranes with higher ionic conductivity substantially reduces the energy footprint for MCDI - approximately 35 kT per ion removed with ED membranes to 15 kT per ion removed with new ion-exchange membranes. Additionally, the new ion-exchange membranes displayed a significantly higher Coulombic efficiency. The talk will showcase how ex-situ properties of ion-exchange membranes, such as ionic conductivity, thickness, and permselectivity, are instrumental for lowering the energy footprint of MCDI.
Note: Figure represents single-cell MCDI operation under constant current with newly prepared ion-exchange membranes. Green line corresponds to cell voltage, while the purple line corresponds to the salt effluent stream.
 D. Bauer, M. Philbrick, B. Vallario in The Water-Energy Nexus: Challenges and Opportunities, 2014.