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

Abstract

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.

Electrochemical Properties of the Composites Based on Multiwall Carbon Nanotubes Modified with Nanoparticles of Mixed Cobalt and Nickel Hydroxides

“…In addition to charging accumulation due to the formation of the EDL, the charge is also accumulated due to Red/Ox-reactions proceeding with the participation of oxygen-containing groups, which are introduced additionally during ozonation. The presence of O-containing groups in the initial MWCNT matrix and an increase in their number after functionalization were confirmed previously by means of thermogravimetric (TG) investigation and СNHO-analysis [5].…”

“…The process was carried out at a temperature of 98 °C for 20 min, then the product was washed with a small amount of distilled water to liberate NaCl, and dried to a constant weight. It was shown previously [5] that nanocomposites obtained using this procedure contain the solid solutions of cobalt and nickel hydroxides.…”

“…MWCNT characterization showed that the outer diameter of the tubes was 10-20 nm, and the diameter of inner channels was 8-15 nm. The thickness of tube walls composed of 6-14 graphene layers was thus 2-5 nm; the average length of the tubes was about 10 μm [4,5].…”

“…For the synthesis of NC Co x Ni (1-x) (OН) 2 / MWCNT and Co x Ni (1-x) (OН) 2 /MWCNT-f(x=0.5), we used the solutions of cobalt and nickel chlorides, and sodium hydroxide as described in detail in [5].…”

Carbon/NiO Compositional Fibers

“…AC are well known to be widely investigated as materials for supercapacitor electrodes, which have such advantages as low cost, large specific surface area and variously shaped porous structure [14]. However, most AC is inferior to metal oxides in terms of capacitance.…”