Multiwalled Carbon Nanotubes: Matrix Nanostructured Composites as Electrode Materials for Supercapacitors

Herein, nanostructured composites (NSCs) based on multiwalled carbon nanotubes (MWCNTs) filled with the individual (IH) and mixed (MH) Ni/Co hydroxides nanoparticles are prepared and an influence of NSC morphology and texture on their electrical capacitance is considered. It is found that MWCNTs have a channel diameter (2-5 nm), external diameter (18-23 nm), and wall width (2-12 nm). In NSCs obtained by precipitation of hydroxides from chloride aqueous solutions in an alkaline medium, the filler particles are formed as nanocrystallites inside the channels as well as aggregates composed of crystallites (up to 10 nm in size) situated on the external MWCNT surface. These aggregates look like islands, 15-16 nm wide, and are at least 200 nm long. Functionalization via ozonation causes nontrivial effects of an increase in the size and anisometry of the MH crystallites. The dependence of the NSC electrical capacitance on the content of fillers appears to be extreme. The content in the range of 5-10 wt% which allows increasing the capacitance by 1.2 and 1.5 times as compared with that for MWCNTs is optimal for scanning rates of 80 and 10 mV s(-1), respectively.