One‐Dimensional Spinel Transition Bimetallic Oxide Composite Carbon Nanofibers (CoFe2O4@CNFs) for Asymmetric Supercapacitors

Abstract CoFe 2 O 4 composite carbon nanofibers (CoFe 2 O 4 @CNFs) are prepared by electrospinning combined with pre‐oxidation, carbonization, and extra annealing under air conditions. The effect of different extra annealing times on the structure, morphology, and electrochemical properties of the resulting CoFe 2 O 4 @CNFs are investigated. CoFe 2 O 4 @CNFs (named as CFO/C‐800‐2) with a spinel structure are successfully prepared after 2 h of extra annealing for CFO/C‐800‐0. CFO/C‐800‐2 shows a mesoporous structure with a mesoporous area of 358 m 2 g −1 . CFO/C‐800‐2 shows pseudocapacitance characteristics with a specific capacity of 591.8 F g −1 at a current density of 1 A g −1 . The capacitance retention rate of the asymmetric supercapacitor assembled by CFO/C‐800‐2 with activated carbon (AC) can reach 87 % in the 0–1.7 V voltage window, and the energy density is 21.4 Wh Kg −1 at a power density of 850 W Kg −1 after 7000 cycles.