Carbon-incorporated Fe₃O₄nanoflakes: high-performance faradaic materials for hybrid capacitive deionization and supercapacitors

Here, we introduce a new strategy using urea for the synthesis of carbon-incorporated 2D Fe3O4 (2D-Fe3O4/C) nanoflakes under solvothermal conditions with the following pyrolysis process under an inert atmosphere. Thanks to the structural advantages of 2D-Fe3O4/C, including 2D flakes providing a larger accessible surface area and exposing more active sites, as well as carbon incorporation promoting electrical conductivity for faster charge transfer, the 2D-Fe3O4/C displays a high specific capacitance of 386 F g-1 at 1 A g-1 in a three-electrode system. More importantly, when further assembled into a hybrid supercapacitor with pre-synthesized NiCo-layered double hydroxides as positive electrodes, the assembled supercapacitor device delivers a high-energy density of 32.5 W h kg-1 at 400 W kg-1 and little capacitance loss with bending angles ranging from 0° to 180°. As another capacitive application in desalination, 2D-Fe3O4/C also shows a high desalination capacity of 28.5 mg g-1 over 7.5 min, which suggests a very high mean desalination rate of 3.8 mg g-1 min-1. Our results not only highlight the significance of 2D metal oxide nanosheets/nanoflakes, but also hold great potential for high-performance capacitive applications in supercapacitors and desalination.