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

Abstract

Summary 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 1170 cm−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 36.200 F g−1 (77 times better than pristine) and 45.100 F g−1 (2.5 times enhancement), respectively. For K2SO4, it was 33.600 F g−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 © 2017 John Wiley & Sons, Ltd.

Recent Progress on Electrochemical Capacitors Based on Carbon Nanotubes

“…Figure 6 shows the effect of the addition of oxygen redox-active molecules on the electrochemical performance of CNTs. Nanotubular materials can be treated (CNTs-T) chemically [62][63][64][65][66][67][68][69][70], electrochemically [59,71,72], photochemically [73,74], and using plasma-induced techniques [75,76]. The chemical modifications are usually performed in concentrated nitric acid or in a mixture of nitric and sulfuric acids.…”

Metal‐organic chemical vapor deposition of anatase titania on multiwalled carbon nanotubes for electrochemical capacitors

“…1,23 For instance, multiwalled carbon nanotubes (MWCNTs), due to their high surface area to volume ratio and facile surface functionalization that promotes polarizability, have been reported as suitable electrodes for charge storage devices. 21,[24][25][26][27] However, the specific capacitance of MWCNTs is far below the theoretical values of 400-500 F g −1 . 28,29 The current drawbacks of carbon-based materials include their low capacitive characteristics, partly because of poor polarizability and wettability associated with the electrode surfaces, which limit the available surfaces for energy storage.…”

“…A Metrohm 797 VA Computrace electrochemical workstation (Metrohm, Switzerland) comprising of a three‐electrode system (Pt counter and Ag/AgCl reference electrodes), 1 M Na 2 SO 4 electrolyte (typically degassed with nitrogen for five min before analysis), a scan range of 0–0.8 V, and scan speeds of 10, 25, 50, 100 and 200 mV s −1 , were used for CV. The C s from the CV curve was calculated by using the following equation: 17,23,26 $$${C}_{S}=\frac{1}{2}\frac{\int \,{idV}}{{ms}\unicode{x02206}V},$$$where i (A), m (g), s (V s −1 ), and Δ V (V) are the current, active material mass, scan speed, and voltage window, respectively. Integration was done by use of the Lorentzian function.…”

“…A Metrohm 797 VA Computrace electrochemical workstation (Metrohm, Switzerland) comprising of a three-electrode system (Pt counter and Ag/AgCl reference electrodes), 1 M Na 2 SO 4 electrolyte (typically degassed with nitrogen for five min before analysis), a scan range of 0-0.8 V, and scan speeds of 10, 25, 50, 100 and 200 mV s −1 , were used for CV. The C s from the CV curve was calculated by using the following equation: 17,23,26…”

Graphene/pyrrolic-structured nitrogen-doped CNT nanocomposite supports for Pd-catalysed Heck coupling and chemoselective hydrogenation of nitroarenes

“…The TGA weight loss under a N 2 atmosphere at temperatures between 25 and 1000 °C reveals the percentage oxygen functionalization on the nanocomposites. The decomposition temperatures of the carbon supports that ranged from 150 to 400, 401 to 500 and 650 to 700 °C and were ascribed to -COOH, -COO-and -OH functional groups, respectively [67][68][69]. G/CNTs and G/N-CNTs-OT possess more stable oxygen functionalities, as only a one-step weight loss was observed between 100 and 900 °C ( Fig.…”