Electrospun amorphous CoOx/C composite nanofibers doped with heteroatoms for symmetric supercapacitors

[Display omitted] •Thiourea not only N and S- containing precursors but also a modifier of the composite nanofiber.•Combined advantages of amorphous and porous structure with heteroatom doping.•As high as a capacitance of 140 F/g even cycling at 10 A/g and a significant cycle ability of 82.4% after 10 000 cycles in two-electrode configuration. Amorphous cobalt oxide nanoparticles were prepared in heteroatom-doped carbon (CoOx/C) composite nanofibers by simple electrospinning and carbonization techniques. In this structure, heteroatom doping mainly provides capacitance and maintains the stability of the nanostructure, while amorphous cobalt oxide not only enhances ion diffusion but also optimizes electronic conduction. The nanofibers were comparatively studied using SEM-EDX, HR-TEM, XRD, Raman, FTIR, and XPS. The obtained amorphous CoOx/C composite nanofibers with heteroatoms doped (C2 electrode) displayed a specific capacitance of 172 F/g at 1 A/g, which is higher than other compositions (102.6 F/g for C0 electrode and 129.5 F/g for C1 electrode) in the two-electrode system. Most importantly, it had a good rate capability of 81.4 % at 10 A/g and a high cycle performance of 82.4 % after 10 000 cycles. In addition, at a specific power of 250 W/kg, it provides a specific energy of 5.97 Wh/kg. The synergistic effect amorphous cobalt oxide and polar effects by heteroatoms (nitrogen, sulfur, and oxygen) increased the electrochemical performance.