Stability engineering of capacitive deionization for water treatment: Degradation mechanisms, material innovations, regeneration strategies, and cell architectures

Abstract

Capacitive deionization (CDI) has emerged as a promising electrochemical technology for low- and moderatesalinity water treatment, polishing, decentralized desalination, selective ion removal, water reuse, and resource recovery. Its mild operating conditions, modular design, and tunable ion-storage mechanisms make CDI attractive when moderate salt removal, flexible operation, or ion-selective treatment is required. However, practical deployment remains limited by long-term performance instability under repeated cycling and realistic feedwater conditions. This review develops a stability-engineering framework for understanding and advancing CDI systems, in which material design, operating conditions, regeneration protocols, and cell configurations are
treated as interrelated factors that determine durability. First, key degradation mechanisms in classical CDI
are analyzed, including asymmetric Faradaic reactions, electrostatic ion trapping, current-collector passivation,
inorganic scaling, and synergistic organic fouling. These coupled processes narrow the effective operating window, increase resistance, block ion-transport pathways, and accelerate capacity decay. Second, recent material innovations are reviewed according to structural architectures, including one-dimensional, two-dimensional, three-dimensional, and hybrid electrode systems, with emphasis on their effects on salt adsorption capacity, salt adsorption rate, conductivity, ion accessibility, selectivity, cycling durability, and regeneration tolerance. Third, operational, antifouling, and regeneration strategies are critically evaluated in relation to voltage-window control, polarity reversal, hydrodynamic optimization, pretreatment, physical flushing, chemical cleaning, thermal treatment, and electrochemical regeneration. Finally, CDI cell architectures are discussed from the perspectives of charge efficiency, mass transfer, fouling distribution, scalability, energy use, regeneration compatibility, and long-term stability. By linking degradation mechanisms with material design, operational control, regeneration strategies, and cell architecture selection, this review identifies stability engineering as a key route toward durable and practically viable CDI systems for water treatment.