Tailoring the surface chemistry of multiwalled carbon nanotubes through acid treatment to enhance the performance of supercapacitor electrodes

There is a need of alternative power sources to fulfill the demand of energy. For this concern, in the present research work, functional groups are attached on the surface of pristine multiwalled carbon nanotubes (PMWCNTs) via acid treatment to fabricate functionalized multiwalled carbon nanotubes (FMWCNTs) and their electrochemical performance are studied. The X-ray diffraction (XRD) analysis shows a change in the diffraction peaks of FMWCNTs as compared to PMWCNTs due to the attachment of functional groups on the surface and outer walls of nanotubes. Raman spectra confirm the enhancement in the D to G band intensity ratios after acid treatment. Attachment of functional groups on the surface of MWCNTs is confirmed by Fourier Transform Infrared Spectroscopy (FTIR). Field enhancement scanning electron microscope (FESEM) images of acid-treated nanotubes demonstrate the tubular morphology with less agglomeration of nanotubes as compared to PMWCNTs. Moreover, transmission electron microscope (TEM) images confirm the existence of well-separated nanotubes with diameter in the range of 10–15 nm. X-ray photoelectron spectroscopy analysis determines the chemical composition of MWCNTs before and after acid treated. Cyclic voltammteric studies confirm the dominance of capacitive process and approximately 72% of capacitance retention at 100 mVsec^–1, indicating a high-rate capability of the sample. FMWCNTs exhibit a high specific capacitance of 320 Fg^–1 at 0.5 Ag^–1 in 1 M KCl aqueous solution as confirmed by galvanostatic charge–discharge analysis. Furthermore, low value of solution resistance (R_s = 0.8 Ω), charge transfer resistance (R_ct = 4.8 Ω), and 88% capacitance retention till 3000 cycles confirm its potential to be used as an electrode material for practical energy storage devices.