NiCo 2 O 4 nanostructure-decorated PAN/lignin based carbon nanofiber electrodes with excellent cyclability for flexible hybrid supercapacitors

Nanostructured binary metal oxide-decorated carbon nanofibers (CNFs) were utilized as flexible electrodes for hybrid supercapacitor applications. Polyacrylonitrile (PAN)/lignin based carbon nanofibers (PAN/lignin CNFs) with different contents of lignin were prepared by electrospinning, stabilization and carbonization. Afterwards, the NiCo2O4 oxides were deposited on the surface of CNFs by a facile hydrothermal method without any toxic reagents. SEM images confirmed that the NiCo2O4 (nanosheet and nanoneedle) nanostructures were uniformly grown on the surface of every carbon fiber. The obtained flexible NiCo2O4-decorated PAN/lignin CNFs with 50% lignin (NiCo2O4@CNF55) electrode exhibited high specific capacitance of the ∼1757 F g−1 at 2 mA cm−2 and excellent cyclability with ∼138% capacitance retention after 5000 cycles at 7 mA cm−2, suggesting lower internal resistance and higher electrochemical reversibility. In addition, the NiCo2O4@CNFs//N-rGO solid state asymmetric supercapacitor devices were assembled in order to evaluate their practical applications. The NiCo2O4@CNF55//N-rGO asymmetric supercapacitor device exhibited a specific capacitance of 134.3 F g−1 at a current densities of 1 A g−1, and possessed a maximum energy density of 47.75 Wh kg−1 with a power density of 799.53 W kg−1.