Core-Shell Composite Fibers for High-Performance Flexible Supercapacitor Electrodes.

Core-shell nanofibers containing poly(acrylic acid) (PAA) and manganese oxide nanoparticles as the core and polypyrrole (PPy) as the shell were fabricated through electrospinning the solution of PAA and manganese ions (PAA/Mn2+ ). The obtained nanofibers were stabilized by 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 the fibers by immersing the fibers in a pyrrole solution where the Fe3+ ions in the fiber polymerized the pyrrole on the fiber surfaces. In the MnO2 @PAA/PPy core-shell composite fibers, MnO2 nanoparticles function as high-capacity materials, while the PPy shell prevents the loss of MnO2 during the charge/discharge process. Such a unique structure makes the composite fibers efficient electrode materials for supercapacitors. The gravimetric specific capacity of the MnO2 @PAA/PPy core-shell composite fibers was 564 F/g based on cyclic voltammetry curves at 10 mV/s and 580 F/g based on galvanostatic charge/discharge studies at 5 A/g. The MnO2 @PAA/PPy core-shell composite fibers also present stable cycling performance with 100% capacitance retention after 5000 cycles.