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

Nguyen Anh Thu Tran; Tran Minh Khoi; Jingoo Kim; Kimin Chae; Yuna Shin; Wook Ahn; Young-Woo Lee; Huu Thang Nguyen; Thi Ngoc Tram Le; Yun Ho Kim; Seung Woo Lee; Younghyun Cho

doi:10.1016/j.watres.2025.123940

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

Water Res. 2025 May 31:284:123940. doi: 10.1016/j.watres.2025.123940. Online ahead of print.

Authors

Affiliations

¹ Department of Energy Engineering, Soonchunhyang University, Asan-si 31538, Republic of Korea; Department of Future Convergence Technology, Soonchunhyang University, Asan-si 31538, Republic of Korea.
² Department of Energy Engineering, Soonchunhyang University, Asan-si 31538, Republic of Korea; Department of Future Convergence Technology, Soonchunhyang University, Asan-si 31538, Republic of Korea; Advanced Energy Research Center, Asan 31538, Republic of Korea.
³ Department of Chemistry, North Carolina State University, Raleigh, NC 27695-79055, USA.
⁴ The George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, 30332, USA.
⁵ Department of Energy Engineering, Soonchunhyang University, Asan-si 31538, Republic of Korea; Department of Future Convergence Technology, Soonchunhyang University, Asan-si 31538, Republic of Korea; Advanced Energy Research Center, Asan 31538, Republic of Korea. Electronic address: yhcho@sch.ac.kr.

PMID: 40513459
DOI: 10.1016/j.watres.2025.123940

Abstract

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.

Keywords: Conducting polymer; Electron mediator; Flow-electrode capacitive deionization; Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate; Pseudocapacitance.