Bismuth Nanoparticles Encapsulated in Nitrogen-Doped Carbon Hierarchical Porous Spheres as a Chloride Ion Capturing Electrode for Capacitive Deionization

Capacitive deionization (CDI) has emerged as an energy-efficient and environmentally sustainable technology for water desalination. While bismuth-based materials show exceptional chloride selectivity and high theoretical capacity, their practical application is limited by inadequate cycling stability. Herein, we report a hierarchically porous Bi/N-doped carbon composite (Bi/NCs-0.6) synthesized through a scalable ultrasonic spray pyrolysis approach using low-cost coal as the precursor. This composite exhibits strong interfacial coupling, which facilitates abundant chloride adsorption sites, efficient electron/ion transport, and markedly improved cycling durability. The electrode delivers a high salt adsorption capacity of 69.14 mg g–1 and a rapid salt adsorption rate of 10.54 mg g–1 min–1 and retains 90% of its capacity over 50 cycles. This study provides valuable insights into the design of robust Bi-based CDI electrodes and demonstrates a feasible route for their large-scale production.