Bioinspired Reduced Graphene Oxide/Polyacrylonitrile‐Based Carbon Fibers/CoFe2O4 Nanocomposite for Flexible Supercapacitors with High Strength and Capacitance

Abstract For the first time, zero‐dimensional (0D) CoFe 2 O 4 nanoparticles, one‐dimensional (1D) polyacrylonitrile‐based carbon fibers (PBCF), and two‐dimensional (2D) reduced graphene oxide (RGO) nanosheets were used as building blocks to create an integrated ternary nanocomposite paper with a nacre‐like microstructure for flexible supercapacitors. Inspired by the “mortar‐brick” toughening mechanism of nacre, hydrogen and covalent bonding were further introduced into the bioinspired paper with 0D CoFe 2 O 4 , 1D PBCF, and 2D RGO to realize increased mechanical properties through the synergistic toughening effects of the interfacial interactions of hydrogen and covalent bonding. These collaboratively lead to enhanced mechanical properties such as high tensile strength, exceptional toughness, and eminent electrical conductivity. When used as a free‐standing flexible electrode, the bioinspired interconnected 3D network exhibits an outstanding volumetric capacity of 240 F ⋅ cm −3 at 10 mV ⋅ s −1 and an excellent cycle life of 2000 cycles for a flexible symmetric supercapacitor device (SSCD). Remarkably, the fabricated flexible SSCD can be cycled reversibly in the voltage range of −1 to 0 V and shows a maximum energy density of 33.33 mW ⋅ h cm −3 , suggesting great potential for practical applications in flexible energy storage devices.