Highly Efficient and Stable Capacitive Deionization Based on a Flower-Like Conjugated Polymer with Double Active-Sites

Abstract

Hybrid capacitive deionization (HCDI) shows promise for desalinating brackish and saline water by utilizing the pseudocapacitive properties of faradaic electrodes. Organic materials, with their low environmental impact and adaptable structures, are attractive for this application. However, their scarcity of active sites and tendency to dissolve in water-based solutions remain significant challenges. Herein, we synthesized a polynaphthalenequinoneimine (PCON) polymer with stable long-range ordered framework and rough three-dimensional floral surface morphology, along with high-density active sites provided by C=O and C=N functional groups, enabling efficient redox reactions and achieving a high Na⁺ capture capability. The synthesized PCON polymer showcases outstanding electroadsorption characteristics and notable structural robustness, attaining an impressive specific capacitance of 500.45 F g⁻¹ at 1 A g⁻¹ and maintaining 86.1% of its original capacitance following 5000 charge–discharge cycles. Benefiting from the superior pseudocapacitive properties of the PCON polymer, we have developed an HCDI system that not only exhibits exceptional salt removal capacity of 100.8 mg g⁻¹ and a remarkable rapid average removal rate of 3.36 mg g⁻¹ min⁻¹ but also maintains 97% of its initial desalination capacity after 50 cycles, thereby distinguishing itself in the field of state-of-the-art desalination technologies with its comprehensive performance that significantly surpasses reported organic capacitive deionization materials. Prospectively, the synthesis paradigm of the double active-sites PCON polymer may be extrapolated to other organic electrodes, heralding new avenues for the design of high-performance desalination systems.