Constructing interconnected hierarchical porous structures and nitrogen-doped carbon nanofibers for superior capacitive deionization

Abstract

Capacitive Deionization (CDI) has emerged as a sustainable and efficient method for desalinating low-salinity water sources. However, CDI materials are often limited by insufficient surface area, slow electron/ion transport, and suboptimal electrolyte wettability, which restrict desalination capacity and rate. Herein, we simultaneously construct interconnected hierarchical porous structures and nitrogen-doping in carbon nanofibers by pyrolyzing polymer nanofiber precursors embedded with Zeolite Imidazolate Framework-8 (ZIF-8) nanoparticles. ZIF-8 nanoparticles serve not only as precise pore-forming templates but also act as a rich source of nitrogen for doping the carbon nanofibers. We optimize the pore structure and nitrogen content of the carbon nanofibers by tuning the diameter of ZIF-8 nanoparticles within the polymer nanofiber precursor, thereby achieving superior CDI performance. This unique structure not only substantially increases the specific surface area and significantly enhances mass transfer processes, but also introduces abundant nitrogen into the porous carbon fibers. This improves their hydrophilicity, adjusts their electronic structure, increases active sites, and greatly boosts the electrodes’ adsorption capacity and desalination efficiency. An electrode constructed from the optimized porous nanofibers with a larger specific surface area (LPCNF) achieves a peak desalination capacity of 68.11 mg/g. Furthermore, the electrode maintains a high salt adsorption capacity (SAC) retention of 93.4 % after 50 cycles, significantly outperforming conventional materials such as activated carbon, graphene, and carbon nanotubes. Overall, the developed method optimizes both the pore structure and enhances the nitrogen content, providing a novel strategy for developing high-performance CDI electrode materials.