Oxygen-modified multiwalled carbon nanotubes: physicochemical properties and capacitor functionality

Multiwalled carbon nanotubes (MWCNTs) have found numerous applications in energy conversion systems. The current work focused on the introduction of oxygen moieties onto the walls of MWCNTs by five different reagents and investigating the associated physicochemical properties. Oxygen-containing groups were introduced onto MWCNTs using an ultrasound water-bath treatment with HNO3, HCl, H2O2 or HCl/HNO3 solution. Physicochemical properties were characterised by Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, Raman, thermal gravimetric analysis, textural characteristics, cyclic voltammetry and electrochemical impedance spectroscopy. The study focus was mainly on linking the physicochemical properties of oxygen-functionalised MWCNTs and suitability in electrochemical capacitors using group one sulfates. From the Fourier transform infrared spectroscopy KBr pellet protocol, peaks at 3400, 2370 and 1170cm(-1) suggest oxygen-containing functionalities on MWCNTs. HNO3 treatment introduced highest oxygen-containing moieties and achieved highest specific capacitance in Li2SO4 and Na2SO4 electrolytes of 36.200Fg(-1) (77 times better than pristine) and 45.100Fg(-1) (2.5 times enhancement), respectively. For K2SO4, it was 33.600Fg(-1) (4.9 times better) with HNO3/HCl-treated samples. Oxygen-functionalised MWCNTs displayed both pseudo and electrochemical double-layer mechanism of enhanced charge storage and cycle stability in group one sulfates electrolytes. The dominating charge storage mechanism was pseudo, and Na2SO4 was the best electrolyte amongst the three group one sulfates investigated. Copyright (c) 2017 John Wiley & Sons, Ltd.