The physical and electrochemical properties of nitrogen-doped carbon nanotube- and reduced graphene oxide-titania nanocomposites

Abstract

This study was aimed at understanding and tuning the electrochemical properties, as well as other associated physicochemical properties, of nitrogen-doped multiwalled carbon nanotubes (N-MWCNTs) for application in electrochemical capacitors (ECs). This was done by synthesising composites of N-MWCNTs with both reduced graphene oxide (RGO) and titania. The study also compared the suitability of composites prepared by either sol-gel or chemical vapour deposition (CVD) methods in EC applications. Suitable composites containing non-doped MWCNTs were also prepared for comparison purposes. The physicochemical properties of the composites were investigated by means of transmission electron microscopy and scanning electron microscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy, Raman spectroscopy, cyclic voltammetry and electrochemical impedance spectroscopy. The study showed a deterioration of EC quality with increase in the pyrrolic N content of N-MWCNTs. The sol-gel was more appropriate method for composite synthesis than CVD since it provided favourable physicochemical properties with higher EC functionality potential. The Warburg pathlength was successfully reduced via synthesis of composites and this enhanced the Cs of N-MWCNTs. The RGO/N-MWCNT composite exhibited the shortest diffusion pathlength and better EC potential. This work has shown that the synthesis of composites containing RGO is a suitable way to positively tune the EC functionality of pyrrolic N-MWCNTs.