Carbon Nanotube/RuO[sub 2] Nanocomposite Electrodes for Supercapacitors

Abstract

Electrochemical characteristics of electrodes for supercapacitors built from RuO 2 /multiwalled carbon nanotube ͑CNT͒ nanocomposites have been investigated. Capacitances have been estimated by cyclic voltammetry at different scan rates from 5-50 mV/s. Electrostatic charge storage as well as pseudofaradaic reactions of RuO 2 nanoparticles have been affected by the surface functionality of CNTs due to the increased hydrophilicity. Such hydrophilicity enables easy access of the solvated ions to the electrode/electrolyte interface, which increases faradaic reaction site number of RuO 2 nanoparticles. The specific capacitance of RuO 2 /pristine CNT nanocomposites based on the combined mass was about 70 F/g (RuO 2 : 13 wt % loading͒, and the specific capacitance based on the mass of RuO 2 was 500 F/g. However, the specific capacitance of RuO 2 /hydrophilic CNT nanocomposites based on the combined mass was about 120 F/g (RuO 2 : 13 wt % loading͒, and the specific capacitance based on the mass of RuO 2 was about 900 F/g. Nanostructured material based on the assembly of carbon nanotubes ͑CNTs͒ have been considered for electrodes of electrochemical energy storage devices, such as Li-ion secondary batteries, 1-3 fuel cell, 4,5 and electrochemical capacitors. 6,7 The CNTs are attractive materials for electrodes of energy storage devices due to their chemical stability, low mass density, good conductivity, and large surface area. 8 Electrochemical capacitors are battery-complementary devices for applications demanding a high power level. 9,10 Two types of electrochemical capacitors are under development: the double layer and redox capacitors. In the former, energy storage arises mainly from the separation of electronic and ionic charges at the interface between high specific-area electrode materials. 11 In the latter, fast faradaic reactions take place at the electrode materials. 12 An electrochemical capacitor of large specific capacitance results when an electrode material that has large specific surface and suitable pore size is combined with a material that can have a fast faradaic reaction. 13 Recently, Niu et al. 6 reported that electrochemical capacitor electrodes prepared from multiwalled CNTs for which the surface is 430 m 2 /g, show the maximum specific capacitance of 113 F/g in solution of 38 wt % H 2 SO 4 used as electrolyte. Ma et al. 14 reported CNT electrodes that showed 15-25 F/g in a solution of 38 wt % H 2 SO 4 . Up to now, the specific capacitances of CNT-based electrodes is between 4 and 146.6 F/g in the solution of H 2 SO 4 . 15 Unfortunately, this value is lower than that of an activated carbon electrode with surface area up to 3000 m 2 /g ͑measured gas adsorption͒. 16 It is a drawback of CNTs to the application of electrochemical capacitors. The modification of the CNT material by a specific additive providing quick pseudocapacitive material such as RuO 2 is another route to enhance capacitance. 17 In this paper, we report on the preparation of RuO 2 nanoparticles as small as 1 nm in diam well dispersed...

Fabrication of CNT/CMK3 Carbon Composites with High Electrical/Thermal Conductive Properties

“…Park et al 21 reported on the preparation of RuO 2 nanoparticles dispersed in CNTs along with their performance as active materials in electrochemical capacitors. Ko and Kim 3 prepared chemically activated multi-walled CNTs (A-CNTs) using KOH, and used it as an additive in the fabrication of MnO 2 electrodes to enhance the performance of MnO 2 -based SCs.…”

Performance of Manganese Oxide/CNTs Composites as Electrode Materials for Electrochemical Capacitors

“…32,33 The values of specific capacitance reported for manganese oxide in the literature range between 150 and 250 F/g. [16][17][18][19][20][21][22][23][24][25]34 These values are far from the theoretical value, ca.…”

Carbon Nanotubes and Carbon Nanotubes/Metal Oxide Heterostructures: Synthesis, Characterization and Electrochemical Property

“…Consequently, the metal oxide coatings on acidtreated CNTs were often nonuniform, although they provided better interaction in comparison with pristine CNTs. Despite these drawbacks, most researchers have used such acid-treated CNTs for various metal oxide coatings, including SnO 2 [160,161,[163][164][165], TiO 2 [159,[166][167][168], RuO 2 [169,170], CeO 2 [162], NiO [171], and mixed oxides [172].…”

“…Among these transition metal oxides, ruthenium oxides are regarded as the most promising electrode material for supercapacitor applications due to their high specific capacitance, highly reversible redox reactions, wide potential window, and very long cycle life [192]. Park et al reported a specific capacitance for CNT/RuO 2 (13 wt %) of 450 F/g at a potential scan rate of 20 mV s -1 , which could be further enhanced, by using hydrous ruthenium oxide and functionalized CNTs, to 800 F/g [170]. Reducing the thickness of the RuO 2 layer to 3 nm led to an even higher capacitance (1170F/g at a potential scan rate of 10 mV s -1 ) [149].…”