Flexible Films Derived from Electrospun Carbon Nanofibers Incorporated with Co 3 O 4 Hollow Nanoparticles as Self‐Supported Electrodes for Electrochemical Capacitors

Flexible porous films are prepared from electrospun carbon nanofibers (CNFs) embedded with Co 3 O 4 hollow nanoparticles (NPs) and are directly applied as self‐supported electrodes for high‐performance electrochemical capacitors. Uniform Co 3 O 4 hollow NPs are well dispersed and/or embedded into each CNF with desirable electrical conductivity. These Co 3 O 4 ‐CNFs intercross each other and form 3D hierarchical porous hybrid films. Benefiting from intriguing structural features, the unique binder‐free Co 3 O 4 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% Co 3 O 4 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 Co 3 O 4 ‐CNFs hybrid films attractive for high‐performance electrochemical capacitors.