Supercapacitor Based On Carbon Nanotubes And Carbon Nanofibers Electrodes

This paper first reviews the advances of the electrode materials, especially the materials based on the carbon nanotubes for supercapacitors. It also summarizes preparation processes, structural performances and applications of carbon nanotubes and carbon nanofibers. TEM, SEM, XRD and BET have been used to characterize the carbon nanotubes and carbon nanofibers, and their electrochemical behaviors have been estimated by the battery instrument and the electrochemical workstation.High purity multiwalled carbon nanotube (MWNT) bundles were prepared by chemical vapor deposition method. The TGA results indicated that the purity was higher than 97%. Most of MWNT bundles were cut short and the BET specific surface area increased from 238 m~2/g to 340 m~2/g after 3h ball milling. Pristine and milled carbon nanotubes were used as electrode materials and the prototype electrochemical supercapacitors were assembled. The cyclic voltammetry and charge/discharge curves were used to evaluate the electrochemical capacitance of MWNTs electrodes. The capacitance of MWNTs electrodes changed from 36 F/g to 72 F/g, which was obtained after 3h ball milling. Compared to the pristine carbon nanotubes, milled carbon nanotubes are more suitable electrode materials for electrochemical supercapacitors.Bamboo-shaped multiwall carbon nanotubes (BS-MWCNTs) activated by KOH with different KOH/CNT mass ratio are applied as electrodes for supercapacitors. The electrochemical capacitance of the activated bamboo-shaped multiwall carbon nanotubes (ABS-MWCNTs) with KOH/CNT mass ratio 3:1 and 7:1 is 1.5 and 3 times that of the normal BS-MWCNTs, respectively. The activated materials still possess nanotubular structure with many defects on the outer walls and open tips that give a significant increase of micropore volume, while keeping a noticeable mesoporosity.Multi-branched carbon nanofibers with porous structures have been synthesized on a Cu catalyst doped with alkali metals. Due to their unique structure and large specific surface area, multi-branched carbon nanofibers are potential candidate for supercapacitor electrode material. Electrochemical performance has been tested using this new type of nanofiber as polarized electrodes. Other one-dimension nano-scale material, such as carbon nanotubes filled with Cu nanoneedles at tips, has also been obtained by adjusting the catalyst ratio properly. Growth mechanism for both materials has been discussed in this paper.