Surface modifications of carbon nanotubes towards tailored electrochemical characteristics

This study evaluated the electrochemical performance of cellulose-based multi-walled carbon nanotubes (MWCNTs) as electrode materials. MWCNTs were subsequently treated with acid, heat, N,N'-dimethylformamide and ferrocene carboxaldehyde to obtain the following samples; a-MWCNTs, t-MWCNTs, DMF-MWCNTs and Fc-MWCNTs, respectively, with the samples isolated at each step. The techniques employed to study the physicochemical properties of the MWCNT samples were transmission and scanning electron microscopes, X-ray photoelectron spectroscopy, thermal gravimetric analysis, cyclic voltammetry, electrochemical impedance spectroscopy, nitrogen sorption analysis and Raman and Fourier transform infrared spectroscopies. The electrochemical properties of the four materials were tested by combining them with Nafion and casting them onto a Pt electrode that formed the working electrode of a three-electrode cell with Ag/AgCl as a reference electrode and a Pt counter electrode. The background electrolyte was 1 MNa2SO4. The a-MWCNTS contained the highest concentration of carboxylic oxygen moieties and resulted in an enhanced specific capacitance (C-s) of 42 F g(-1) with the smallest voltage window of 0.30 V. The DMF-MWCNTs and t-MWCNTs had the most stable cycle stabilities and enhanced kinetic response of the electrochemical current. The Fc-MWCNTS exhibited the broadest capacitive voltage window of 0.80 V against an Ag/AgCl reference electrode, the highest specific energy density of 2.70 Wh kg(-1) and the second highest C-s of 30 F g(-1). The treatment protocols demonstrate material tailoring strategies that enable a comparison of the effect of carboxylic acid, phenolic and lactone moieties on MWCNTs and the resulting associated specific energy density, kinetic response, diffusion path length, cycle life and operational voltage window of the electrode material in electrochemical capacitors.

Automated summary

This study evaluated the electrochemical performance of cellulose-based multi-walled carbon nanotubes (MWCNTs) as electrode materials after different treatment protocols. The results showed that treatment methods affect the specific capacitance, cycle stability, and electrochemical properties of the materials.