Core–Shell\nComposite Fibers for High-Performance Flexible Supercapacitor Electrodes

Abstract

Core–shell\nnanofibers containing poly­(acrylic acid) (PAA) and manganese oxide\nnanoparticles as the core and polypyrrole (PPy) as the shell were\nfabricated through electrospinning the solution of PAA and manganese\nions (PAA/Mn²⁺). The obtained nanofibers were stabilized\nby Fe³⁺ through the interaction between Fe³⁺ ions and carboxylate groups. Subsequent oxidation of Mn²⁺ by KMnO₄ produced uniform manganese dioxide (MnO₂) nanoparticles in the fibers. A PPy shell was created on\nthe fibers by immersing the fibers in a pyrrole solution where the\nFe³⁺ ions in the fiber polymerized the pyrrole on the fiber\nsurfaces. In the MnO₂@PAA/PPy core–shell composite\nfibers, MnO₂ nanoparticles function as high-capacity materials,\nwhile the PPy shell prevents the loss of MnO₂ during the\ncharge/discharge process. Such a unique structure makes the composite\nfibers efficient electrode materials for supercapacitors. The gravimetric\nspecific capacity of the MnO₂@PAA/PPy core–shell\ncomposite fibers was 564 F/g based on cyclic voltammetry curves at\n10 mV/s and 580 F/g based on galvanostatic charge/discharge studies\nat 5 A/g. The MnO₂@PAA/PPy core–shell composite\nfibers also present stable cycling performance with 100% capacitance\nretention after 5000 cycles.