Multi-walled carbon nanotube-coated cotton fabric for possible energy storage devices

A conducting cotton fabric with a resistance of < 1.5 k Omega cm(-2) was obtained by dip coating of multi-walled carbon nanotubes (MWCNTs) dispersed in a surfactant, sodium dodecyl sulphate (SDS). The dip coating was repeated up to 20 times to increase the loading of MWCNT as observed from optical absorption spectra (lambda(max) = 442 nm). The field emission scanning electron microscopy (FE-SEM) image of coated fabric at different magnifications shows micro-fibril structure. Energy-dispersive X-ray analysis (EDXA) spectra show peaks for carbon and other constituent elements of SDS, Na and S. In order to improve the functionality of loaded MWCNT, the coated fabric was treated with 5% HNO3 for 3 h. For such a sample, the resistance decreased significantly to 1.5 k Omega cm(-2), whereas it is 2.0 and 2.5 k Omega cm(-2) for untreated and KOH-treated sample. This is in corroboration with I-V characteristics, and is attributed to increased loading of MWCNT through hydrogen bonding with glycosidic group present in cotton (cellulose) fibres. The series capacitance of the MWCNT-coated fabric is about 40 mu F cm(-2), which is found to decrease with the increase in frequency, close to zero at about 20 kHz. A capacitor formed by placing two MWCNT-coated fabrics between etched PCB plates (terminal contacts) shows the charging capacity of about 1 F.