Fabrication of amorphous carbon-coated NiO nanofibers for electrochemical capacitor applications

Abstract

Amorphous carbon-coated nickel oxide nanofibers (NiC NFs) were fabricated using vapor deposition polymerization (VDP) on electrospun nickel oxide nanofibers (NiO NFs), followed by carbonization. To decorate the surface with amorphous carbon, the NiO NF starting materials were prepared by electrospinning a PVP solution containing a nickel oxide precursor (NiAc₂·4H₂O) and calcining the electrospun NFs. Then, polypyrrole (PPy)-coated NiO nanofibers (NiP NFs) were fabricated as intermediate materials using the pyrrole monomer in the VDP method. Finally, carbonization of the NiP NFs converted the PPy into amorphous carbon and thereby formed the NiC NFs. According to X-ray diffraction (XRD) and Barrett–Joyner–Halenda (BJH) analyses, the NiO structure was maintained during the PPy coating and heat treatment processes. Furthermore, a new pore structure was formed with each fabrication step. The NiC NFs were used as electrochemical capacitors (ECs) with 1 M KOH as the electrolyte. The electrochemical results show that NiC NFs with a thin coating (NiC_L) had a higher specific capacitance (288 F g⁻¹ at 0.3 A g⁻¹) and longer cycle stabilization (89% capacitance maintained after 3000 cycles) than pristine NiO NFs (221 F g⁻¹ at 0.3 A g⁻¹; 56% capacitance maintained after 3000 cycles). Herein, the synthetic methodology is an effective route to obtain hybrid core (inorganic)–shell (organic) nanostructures for electrochemical applications.