Carbon-incorporated Fe3O4 nanoflakes: high-performance faradaic materials for hybrid capacitive deionization and supercapacitors

Abstract

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.