Membrane-Free Polymer-Based Faradaic Deionization System for Enhanced Desalination

The development of cost-effective and energy-efficient water desalination technologies remains a critical challenge, particularly for treating brackish water. Herein, we present a membrane-free, dual-polymer electrochemical deionization system that leverages the complementary ion selectivities of polyaniline chloride (PAni-Cl) and poly(naphthalene diimide-ethylenediamine) (PNDIE) to achieve simultaneous sodium and chloride ion removal. By eliminating ion-exchange membranes and utilizing a simple separator, the proposed system minimizes operational complexity and cost while maintaining efficient ionic transport. Initially, the electropolymerized PAni-Cl buckypaper electrode exhibited enhanced electronic conductivity and remarkable cycling stability, retaining 84% of its initial performance after 800 cycles (15 days of operation). Comparative evaluation of three cell architectures, a symmetric CDI cell, a hybrid YP80F//PNDIE cell, and a full polymer-based cell, revealed that the dual-polymer configuration outperforms conventional setups, attaining a salt removal capacity of up to 64 mg·g^-1 after 80 cycles in 50 mM NaCl (50 h test). Moreover, the system demonstrated promising desalination performance in simulated brackish water containing mixed cations, highlighting its practical applicability. These findings establish dual-polymer, membrane-free deionization cells as a promising platform for next-generation, selective, and sustainable water treatment technologies.