P-phenylenediamine-mediated activated carbon slurry electrode for enhanced flow-electrode capacitive deionization

초록

Over the past two decades, capacitive deionization (CDI) has garnered significant attention in water treatment owing to its energy efficiency and cost-effectiveness. Flow-electrode CDI (FCDI) enables continuous operation using a flowable carbon slurry electrode; however, its performance is often limited by poor electronic percolation and low charge-transfer efficiency within the slurry. Herein, we incorporated para-phenylenediamine (pPD) as a soluble organic redox-active mediator into an activated carbon (AC) slurry flow electrode to overcome these limitations. The results demonstrate that pPD undergoes reversible proton-coupled redox reactions (two-proton and two-electron transfer) and facilitates electron transport within the slurry by acting as a molecular electron shuttle and conductive bridge between isolated carbon particles, thereby enhancing charge storage and interfacial charge transfer. The FCDI system, utilizing an optimized pPD concentration of 0.15 M under short-circuited closed-cycle (SCC) operation at 1.2 V with a 35 g/L NaCl feed, achieved a 46% increase in salt removal efficiency and a 48% increase in salt removal rate compared with the pristine AC electrode. Electrochemical characterization confirmed the pseudocapacitive contribution and reduced charge transfer resistance. Furthermore, system performance was systematically evaluated under various operating conditions, including electrode flow rate, feed concentration, and applied voltage. This study provides a cost-effective strategy for upgrading conventional carbon slurries for high-efficiency desalination in FCDI. © 2026 Elsevier B.V.

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