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

CoFe2O4 composite carbon nanofibers (CoFe2O4@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 CoFe2O4@CNFs are investigated. CoFe2O4@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.