Capacitive Deionization Using Organic Mixed Ion Electron Conductors

The increasing demand for freshwater, coupled with the retreat of mountain glaciers, has elevated water scarcity to a global concern. To address this issue, numerous desalination technologies, including Reverse Osmosis, Multi-Stage Flash, Multi-Effect Distillation, and Electrodialysis, have been developed. Capacitive Deionization (CDI) stands out as a promising and relatively underutilized water treatment method with the potential for low energy consumption and cost-effectiveness. Over the past two decades, materials with improved durability, high salt absorption capacity, hydrophilicity, and sufficient conductivity for efficient operation have been developed.
Here, we demonstrate the effectiveness of a hybrid CDI system that utilizes poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) and poly(3,4-propylenedioxythiophene(oligo(ether))-2,2-dimethyl) (ProDOT(OE)-DMP) as the redox active electrode materials. Both PEDOT:PSS and ProDOT(OE)-DMP can conduct ions and electronic charge carriers, enabling more efficient salt sequestration from aqueous solution than conventional impermeable materials like activated carbon. In this device, PEDOT:PSS film functions as a cation transporter, while ProDOT(OE)-DMP film acts as an anion transporter. The device exhibits high charge storage capacity and strong cycle stability with salt adsorption capacities on par with leading CDI materials, outperforming activated carbon at higher feed stream concentrations. This study reveals distinct differences in ion transport mechanisms between these conducting polymers and activated carbon, demonstrating the potential of organic electrochemical materials for water desalination.