Flexible Films Derived from Electrospun Carbon Nanofibers Incorporated with Co3O4 Hollow Nanoparticles as Self‐Supported Electrodes for Electrochemical Capacitors

Flexible porous films are prepared from electrospun carbon nanofibers (CNFs) embedded with Co₃O₄ hollow nanoparticles (NPs) and are directly applied as self‐supported electrodes for high‐performance electrochemical capacitors. Uniform Co₃O₄ hollow NPs are well dispersed and/or embedded into each CNF with desirable electrical conductivity. These Co₃O₄‐CNFs intercross each other and form 3D hierarchical porous hybrid films. Benefiting from intriguing structural features, the unique binder‐free Co₃O₄ hollow NPs/CNF hybrid film electrodes exhibit high specific capacitance (SC), excellent rate capability and cycling stability. As an example, the flexible hybrid film with loading of 35.9 wt% Co₃O₄ delivers a SC of 556 F g^?1 at a current density of 1 A g^?1, and 403 F g^?1 even at a very high current density of 12 A g^?1. Remarkably, almost no decay in SC is found after continuous charge/discharge cycling for 2000 cycles at 4 A g^?1. This exceptional electrochemical performance makes such novel self‐supported Co₃O₄‐CNFs hybrid films attractive for high‐performance electrochemical capacitors.