Chemical-Free Regeneration of Scaled Capacitive Deionization Electrodes Using Alternating Polarization

Mineral scaling on carbon electrodes remains a critical limitation to the long-term performance of capacitive deionization (CDI) systems treating hard and alkaline waters. In this study, alternating polarization (AP) is investigated as an in situ electrochemical regeneration strategy to reverse cathodic scaling in flow-through CDI treating a feed containing 5 mM NaCl, 5 mM NaHCO3, and 2.5 mM CaCl2 under three modes: conventional cycling (control), delayed AP introduced after fouling developed, and immediate AP implemented from the first cycle. Under conventional operation, cathodic scaling reduced the salt adsorption capacity (SAC) to 5.9 ± 0.2 mg/g, increased cathode mass from 0.208 ± 0.004 g (pristine) to 0.353 ± 0.054 g, and decreased specific capacitance to 28 ± 2 F/g, accompanied by extensive pore blockage and carbonate deposition observed by SEM and BET measurements. Application of delayed AP restored electrode functionality, increasing SAC to 8.9 ± 0.6 mg/g and specific capacitance to 56 ± 2 F/g while reducing the cathode mass to 0.212 ± 0.007 g and removing surface precipitates. The immediate AP operation reduced the extent of scale formation from cycle 1, maintaining SAC at 8.4 ± 0.2 mg/g throughout operation, with stable physical and electrochemical properties. These improvements are attributed to periodic polarity reversal, which induces alternating alkaline and acidic microenvironments at the electrode surface and promotes the electrochemical dissolution of carbonate phases during anodic polarization. Overall, this work establishes AP as a simple, chemical-free operational strategy for both preventing and reversing cathodic mineral scaling, thereby enabling sustained CDI performance and mitigating capacity loss over the tested operational periods in complex water matrices.