Flexible nitrogen-doped carbon nanofiber-reinforced hierarchical hollow iron oxide nanorods as a binder-free electrode for efficient capacitive deionization

Abundant endeavors have been undertaken to explore high-quality and inexpensive materials for capacitive deionization desalination. However, one major problem is the sluggish adsorption rate and inferior adsorption performance of these materials in practical applications. Herein, nitrogen-doped carbon nanofiber-reinforced hierarchical hollow iron oxide nanorods grown on electrospinning carbon nanofibers (denoted Fe2O3@CNFs) were rationally designed and synthesized for high-efficiency capacitive deionization. Such composition and distinctive hierarchical porous structure prevent agglomeration of Fe2O3 nanorods, boosting the ionic/electronic transport through the synergistic effect between the Fe2O3 nanorods and N-doped carbon nanofibers. When employed as a cathode for capacitive deionization without adding any polymeric binder or conductive additives, this material exhibits a high adsorption capacity of 114.97 mg/g and a rapid salt adsorption rate (7.79 mg/g min). Moreover, the sodium storage mechanism was revealed through ex situ XRD, EDX mapping and ex situ XPS. Density functional theory (DFT) calculations reveal that the electrons are redistributed at the heterojunction interface, refining the electrochemical activity. This work is anticipated to afford an innovative path for the development of porous transition metal oxide-based fibers with outstanding effectiveness and stability toward environmental research of high-performance capacitive deionization. [Display omitted] •A free-standing hierarchical hollow Fe2O3@CNFs hybrid electrode was fabricated.•A high electrosorption capacity and a rapid salt adsorption rate were achieved.•The hollow structure alleviates volume expansion and facilitates ion diffusion.•The faradic reaction and electroadsorption coupling removal mechanism was proven.•DFT were implemented to provide in-depth insights into the storage mechanism.