Conductive bismuth-based metal-organic frameworks with dual redox sites for efficient capacitive deionization

Abstract

Bismuth (Bi), possessing intrinsic faradaic properties, has garnered significant attention as a highly promising anode material for capacitive deionization (CDI) due to its superior capacity and strong Cl⁻ affinity. However, the substantial volume expansion and pronounced pulverization of the Bi electrode during the chlorination/dechlorination conversion process significantly compromise its cycling stability. Herein, conductive porous Bi-based metal–organic framework (Bi-Fc-MOF) nanoflowers with dual redox active sites were strategically designed and fabricated as CDI anodes, leveraging the organic linker coordination effect. The organic linker strategically disperses Bi centers at the molecular level within the framework, effectively preventing the agglomeration and fragmentation of Bi particles and thus ensuring long-term cycling performance. The synergistic mechanism involving Bi node conversion reactions and the Fe²⁺/Fe³⁺ redox couple charge compensation effect from the ferrocene center enhances the Cl⁻ capture. Owing to these unique and advantageous features, Bi-Fc-MOF exhibits exceptional dechlorination capacity (107.21 mg g⁻¹), high charge efficiency (0.93), and outstanding long-term cycling stability (92.26 % after 50 cycles). Impressively, the systematic ex-situ characterization revealed the synergistic Cl⁻ storage mechanism of the conversion reaction-coupled charge compensation effect in Bi-Fc-MOF. This study offers innovative insights into the design and development of advanced high-performance CDI anode materials