A redox-mediated polymer with extended π-delocalization for efficient Cr3+ elimination via capacitive deionization

• A redox-active polymer with stable molecular structure and electron affinity is designed. • The fast, stable and efficient Cr 3+ capture can be achieved for the polymer electrode. • A capacitive deionization device is constructed to possess high electro-adsorption capability. • An integrated desalination system achieves water treatment, dye removal , and energy recovery. The removal of chromium ions (Cr 3+ ) from wastewater is crucial for mitigating heavy metal pollution and ensuring environmental safety, as excessive Cr 3+ concentrations act as hazardous pollutants. Capacitive deionization (CDI) technology, recognized for its environmental friendliness, low energy consumption, and high efficiency, offers a promising solution for heavy metal ion removal. However, developing stable and efficient CDI electrodes for Cr 3+ removal remains a significant challenge. This study introduces a novel redox-active organic polymer material, denoted as PND, featuring an extended π-conjugated plane, abundant redox-active sites, and enhanced electron delocalization. The C O and C N redox-active sites on the polymer chain further improve its electrosorption capacity for Cr 3+ . The PND-based CDI device achieves an exceptional Cr 3+ removal capacity of 1143.8 mg g −1 with a rapid time-average removal rate of 170.4 mg g −1 min −1 , outperforming most existing heavy metal ion removal technologies while maintaining consistent efficiency over multiple cycles. Ex situ XPS analysis and kinetic studies reveal the reversible electro-adsorption mechanism of Cr 3+ . Additionally, a three-stage CDI system demonstrates practical applications in solar-driven multi-stage chromium removal and cationic dye elimination, highlighting its potential for real-world environmental remediation. This work provides a sustainable strategy for Cr 3+ removal and advances electrochemical water treatment technologies.