Designing a dual-functional redox-active polymer electrode for high-efficiency electrochemical desalination

The emergence of hybrid capacitive deionization (HCDI), utilizing faradaic electrodes with pseudocapacitive properties, offers a promising electrochemical solution for water desalination and purification. Despite the increasing interest in organic materials for faradaic electrodes, their widespread use in HCDI devices is still hindered by obstacles about insufficient redox-active sites and low stability in aqueous environments. To address these challenges, we introduce a novel dual-functional redox-active polymer, named PZPS, which features a rigid conjugated backbone with dual-redox centers (CN and SO bonds). This unique molecular design, along with extensive π-electron delocalization across the strong polymeric structure, significantly improves pseudocapacitive Na⁺ coordination and ensures remarkable stability in aqueous solution. As an electrode, the PZPS polymer exhibits an impressive specific capacitance and excellent cyclability, maintaining 98.04 % of its initial capacitance after 10,000 cycles. Consequently, a high-performance HCDI device with the PZPS electrode demonstrates impressive electrochemical desalination capabilities. It achieves a substantial salt removal capacity of 58.82 mg g⁻¹ at 1.2 V, a rapid average removal rate of 1.96 mg g⁻¹ min⁻¹, and remarkable regeneration stability (∼93.15 % after 50 cycles). These results highlight the electrochemical advantages of the PZPS-based HCDI device and underscore its significant potential for highly efficient desalination applications.