High-Efficiency Electrochemical Desalination: The Role of a Rigid Pseudocapacitive Polymer Electrode with Diverse Active Sites

Hybrid capacitive deionization (HCDI) emerges as a burgeoning electrochemical desalination technology due to the utilization of profitable pseudocapacitive reactions. Although tunable organic compounds are potential faradaic electrode materials, their insufficient active sites and high water-solubility restrict practical HCDI applications. Herein, a pseudocapacitive organic polymer (PNDS) is proposed with diverse redox-active sites for electrochemical deionization. The pronounced molecular aromaticity and strong π-electron delocalization not only endow PNDS polymer with framework rigidity, but refine its electronic structure to bolster redox activity and electron affinity. As an electrode material, the PNDS polymer demonstrates a substantial pseudocapacitive capacitance of 390 F g⁻¹ and sustains long-term stability at 96.3% after 5000 cycles, surpassing reported Na⁺-capturing organic electrodes. In-operando monitoring techniques and theoretical calculations reveal efficient Na⁺ capture at the C═N and C═O redox-active sites within the PNDS electrode during repeated electrosorption processes. As a conceptual demonstration, a high-performance HCDI device equipped with the PNDS electrode exhibits an impressive salt removal capacity (66.4 mg g⁻¹), a rapid removal rate (2.2 mg g⁻¹ min⁻¹) and stable regeneration property. More importantly, an integrated desalination system is engineered to rapidly and repeatedly treat saltwater resources for human consumption and agricultural irrigation, highlighting its promising prospects for high-efficiency desalination applications.