Enhanced salt removal in flow-electrode capacitive deionization using PEDOT:PSS as an electron mediator

Capacitive deionization (CDI) is an energy-efficient and environment-friendly water desalination technology that removes salt ions via electrosorption on porous electrodes. Specifically, CDI using flowable electrodes (FCDI) enables continuous desalination without needing discharging, due to the continuous flow of suspended activated carbon (AC) particles. However, its salt removal performance is limited by the insufficient interparticle electrical connectivity between AC particles. To overcome this drawback, we introduce poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), a well-known conducting polymer with excellent electrical conductivity, high stability, and good compatibility with aqueous environments, into the aqueous slurry electrode to form efficient electrical bridges among AC particles. Rather than serving as a primary ion-sorbing material, PEDOT:PSS functions as an electron mediator, enhancing charge transfer and ion electrosorption within the flow electrode. Furthermore, a conductivity-optimized doping strategy was employed to maximize the electron mediation capability of PEDOT:PSS. This simple and scalable approach significantly improved salt removal efficiency from 18.05 % (pristine AC) to 61.57 %-an enhancement of over 3.4 times-while the average salt removal rate (ASRR) increased by 3.6 times with high energy efficiency. These results demonstrate a novel application of PEDOT:PSS as an electron mediator in FCDI, offering a low-complexity yet highly effective strategy to overcome conductivity limitations of conventional flow electrodes.