Selected values of specific capacitances obtained for thin films of carbon nanotubes.
Abstract
This review is focused on the theoretical and practical aspects of electrochemical capacitors based on carbon nanotubes. In particular, recent improvements in the capacitance properties of the systems are discussed. In the first part, the charge storage mechanisms of the electrochemical capacitors are briefly described. The next part of the review is devoted to the capacitance properties of pristine single- and multi-walled carbon nanotubes. The major portion of the review is focused on the capacitance properties of modified carbon nanotubes. The electrochemical properties of nanotubes with boron, nitrogen, and other atoms incorporated into the carbon network structure as well as nanotubes modified with different functional groups are discussed. Special attention is paid to the composites of carbon nanotubes and conducting polymers, transition metal oxides, carbon nanostructures, and carbon gels. In all cases, the influences of different parameters such as porosity, structure of the electroactive layer, conductivity of the layer, nature of the heteroatoms, solvent and supporting electrolyte on the capacitance performance of hybrid materials are discussed. Finally, the capacitance properties of different systems containing carbon nanotubes are compared and summarized.
Keywords
- carbon nanotubes
- carbon nanoparticles
- conducting polymers
- composites
- electrochemical capacitors
- charge storage materials
1. Introduction
The last two decades can be considered a nanotechnology revolution. With each passing day, increasing attention is paid to the discovery of new nanoscale materials due to the miniaturization of devices in many areas. Nanomaterials are everywhere, from cosmetics and clothes to medicine and electronic devices. At the same time, the increased development of electronic devices requiring energy storage systems, such as batteries and supercapacitors, is starting to play a crucial role in everyday life. Supercapacitors, also called electrochemical capacitors, are energy saving units that can provide a huge amount of energy in a short time. Compared with batteries, electrochemical capacitors offer great advantages of high power capability, high rates of charge and discharge, high cycle life, flexible packaging and low weight [1, 2, 3, 4].
An interesting class of nanomaterial for storage devices is carbon nanotubes due to their large open surface that is completely exposed to electrolyte ions, good electrical conductivity, high surface area, mechanical strength, good corrosion resistance, chemical stability and low mass density [4, 5, 6, 7, 8]. However, so far, pristine CNTs have not met the commercial requirements for energy storage devices applications due to their poor dispersion in solvents, low electrochemical characteristics in the electrolytes, and low specific capacitance [7, 8]. The capacitance properties of carbon nanotubes may be improved by surface functionalization or by the formation of composites with redox-active systems such as conducting polymers or metal oxides. On the other hand, carbon nanotubes are excellent conducting supports to improve the properties of materials with poor conductivity, stability, and capacitance performance. Hence, carbon nanotubes-based nanocomposites or nanohybrids have recently been intensively developed because of their superior properties compared to the individual component alone. Much research on supercapacitors has aimed at increasing power and energy densities as well as lowering fabrication cost [8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18].
The objective of this review is to highlight theoretical and practical aspects of the capacitance properties of carbon nanotubes and their composites. In particular, recent progress in improving the capacitance properties of systems based on carbon nanotubes is discussed. In the first part, the charge storage mechanisms in electrochemical capacitors are briefly described. The next part of the review is devoted to the capacitance properties of pristine carbon nanotubes and carbon nanotubes modified by heteroatoms or functional groups. Special attention is paid to the composites of carbon nanotubes with conducting polymers, carbon nanostructures, transition metal oxides, and carbon gels.
2. Principles and mechanism of charge storage
Electrochemical energy storage may be classified as encompassing either batteries or electrochemical capacitors (ECs), which are also known as supercapacitors, ultracapacitors, electrical double-layer capacitors, pseudocapacitors, gold capacitors or power coaches [19, 20, 21]. Supercapacitors fill the gap between batteries that exhibit high energy density and high power density conventional capacitors, covering several orders of magnitude both in energy and in power density. Batteries compared to supercapacitors store and deliver more energy with slower charge and discharge times. In the case of conventional capacitors, they have very high energy density in comparison to supercapacitors. Supercapacitors also exhibit low heating level, safety, long-term operation stability, low weight, and flexible packaging [4, 22, 23]. Due to these properties of semiconductors, they can be applied in many fields of electrotechnology. They can be used in electric and hybrid vehicles [3, 24, 25], high-energy pulsed lasers [26], mobile phones [26, 27, 28], laptops [27], and cameras [27, 28].
The charge-storage mechanism of electrochemical capacitors is controlled by two principal mechanisms: (i) a non-Faradaic electrostatic interaction resulting from ion adsorption at the electrode/electrolyte interface defined as electric-double layer capacitance (EDLC) (Figure 1a) and (ii) an electrochemical oxidation/reduction reaction in electroactive materials accompanied with Faradaic charge transfer named pseudocapacitance (Figure 1b) [4, 29, 30, 31, 32].
Typical supercapacitors consist of two electrodes separated by a dielectric material or electrolyte solution. In the case of EDLC, where the capacitance comes from the electrostatic charge accumulated at the electrode/electrolyte interface and strongly depends on the surface area of the electrode accessible to the electrolyte ions, mostly porous carbons are used as electrode materials due to their low price, facile synthesis, and sustainability. They are prepared by heat treatment and subsequent chemical activation with organic materials or, in the case of “carbide-derived carbons” (CDCs), by extracting metal atoms in metal carbides. More exotic materials, such as carbon nanotubes (CNTs) and graphene, are also being developed for supercapacitor applications. The operating voltage of supercapacitors depends on the solvent and electrolytes separating both electrodes. Tetraethylammonium tetrafluoroborate is often used as the supporting electrolyte in organic solvents. This salt offers a relatively high operating voltage of approximately 2.5 V and a high ionic conductivity of 20–60 mS cm−1. In aqueous solutions, a maximum potential of 1.2 V can be obtained. Moreover, room-temperature ionic liquids with an operating voltage as high as 4 V could also be used as electrolyte systems. However, supercapacitors based on ionic liquids have poor device power performance due to their low ionic conductivity, i.e., below 20 mS cm−1 [23, 30, 33].
The specific capacitance for EDLC is assumed to follow that of a parallel-plate capacitor:
where
where
In contrast to EDLC, pseudocapacitance results from faradaic fast reversible redox reactions involving electrode material. During electrochemical reactions, the electrode material is reduced or oxidized and doped with counterions from the electrolyte solution. In this case, conducting polymers and metal oxides or hydroxides as electrode materials are used [30]. High-area carbon electrodes also exhibit a small pseudocapacitance component due to electrochemically active redox functionalities [22]. Pseudocapacitance is described by the following equation:
where Δ
The maximum energy stored in supercapacitors is given by
where
where
The electrode is one of the most important components for charge storage and plays a crucial role in determining the energy and power density of supercapacitors [29]. In EDLC, the high surface area resulting from the highly microporous structure of carbon electrode materials such as carbon aerogels, carbon black or carbon cloth is unfavorable for electrolyte wetting and rapid ionic motions, especially at high current loads [22]. The most frequently used activated carbon electrodes exhibit low electrolyte accessibility and poor electrical conductivity. These two effects are responsible for limited energy density and high internal resistance. For this reason, carbon nanotubes (CNTs) with nanoscale size, controllable size distribution, large surface area, high mesoporosity, electrolyte accessibility, and good electrical properties are very promising candidates for replacing carbon materials as the electrode materials in high-performance capacitors. Because of this fact, an extended part of this work will focus on supercapacitors based on carbon nanotubes [4, 29].
3. Capacitance properties of single- and multi-walled carbon nanotubes
Carbon nanotubes exhibit large open surface area, excellent mechanical strength, chemical stability, low mass density, and relatively good electrical conductivity. All these properties make them a very good candidate for the electroactive material in charge storage devices. In these capacitors, the ions of electrolyte are adsorbed on the charged surface of carbon nanotubes, producing a Helmholtz layer. The capacitance properties of these systems depend on the number of graphene walls (single-, double-, or multi-wall), the nature of the electrode material, the composition of the electrolyte solution, and the structure of the carbon nanotube layer. The specific capacitance of pristine CNTs is relatively low and ranges from 2 to 45 F g−1 for SWCNTs [35, 36, 37, 38, 39, 40, 41, 42] and 3 to 80 F g−1 for MWCNTs [36, 37, 38, 42, 43, 44]. The capacitance properties of thin films of CNTs are collected in Table 1.
Carbon nanostructure | Specific capacitance (F g−1) | Experimental conditions | Reference |
---|---|---|---|
SWCNTs | 2 | 0.1 M Na2SO4 | [39] |
17 | 1 M NaCl | [40] | |
18 | 1 M NaCl | [35] | |
19 | 5 M KOH | [35] | |
20 | 6 M KOH | [41] | |
21 | 1 M NaCl | [35] | |
24 | 7 M H2SO4 | [35] | |
40 | 6 M KOH | [38] | |
64 | 1 M H2SO4 | [42] | |
MWCNTs | 3 | 7 M KOH | [43] |
9 | 7 M KOH | [43] | |
14 | 1 M H2SO4 | [42] | |
14 | 6 M KOH | [38] | |
17 | 4 M H2SO4 | [43] | |
26 | 4 M H2SO4 | [43] | |
30 | 1 M H2SO4 | [44] | |
36 | 6 M KOH | [38] | |
38 | 1 M Na2SO4 | [44] | |
62 | 6 M KOH | [38] | |
78 | 1 M H2SO4 | [38] | |
80 | 6 M KOH | [38] |
Such a large scattering of reported specific capacitance values is mainly related to the different procedures of CNT deposition on the conducting electrode surface and, therefore, different structures of CNTs films. Carbon nanotubes can be attached to electrodes by direct growth [45], manual manipulation [46], random spreading [47], deposition in a dc current electric field [48], or gas flow [49]. Specially designed substrates are used for film formation of vertically oriented CNTs [50, 51, 52, 53]. Two of the most common orientations of CNTs are displayed schematically in Figure 3. In general, films of vertically oriented carbon nanotubes exhibit much better electrical and capacitance properties in comparison to films formed from randomly oriented nanotubes [6, 50, 54, 55, 56, 57]. Figure 4 shows the structure of the SWCNT layer formed under CVD growth procedure. The highest specific capacitance of 52 F g−1 and excellent electrochemical stability were reported for such vertical structures of SWCNTs [55].
4. Covalent modification of carbon nanotubes and their capacitance properties
The covalent functionalization of carbon nanotubes provides modification of their physicochemical properties. Insertion of functional groups to the carbon network solves the problem of their poor dispersion capability. Stable dispersions of modified carbon nanotubes are particularly important in the formation of thin films of capacitors or capacitive devices. Moreover, tethering electron-donating or electron-withdrawing groups on CNT surfaces changes their electronic properties by the doping effect [22, 58, 59, 60, 61, 62]. Such groups exhibit electrochemical activity resulting in a pseudo-Faradaic capacitance effect.
Park and co-workers showed the relationship between the electrochemical activity of functional groups attached to the CNT surface and their capacitive characteristics [58]. They found that MWCNTs covalently functionalized by carboxylic, sulfonic, and amine groups (Figure 5) showed a two- to fourfold increase in capacitance over that of pristine MWCNTs due to pseudocapacitive charging-discharging arising from the presence of functional groups. Functionalized CNTs also form more stable dispersions in deionized water and polar organic solvents. Such dispersions can be used in the formation of mechanically stable and uniform capacitor films. Functionalized CNTs, however, exhibit a lower surface area due to the reduction in the average pore size as a consequence of the presence of surface functional groups [58].
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. Cyclic voltammograms recorded for raw CNTs exhibit pseudorectangular cathodic and anodic profiles, which are the characteristics of ideal capacitors. In the case of CNTs-T, a pair of voltammetric peaks is observed. They are related to the redox reactions of functional groups on the CNTs-T surface:
A higher current observed for CNTs-T suggests that their surface area is larger compared to that of raw CNTs. The surface of oxygen-containing functional groups also decreases surface resistivity and enhances surface wettability, offering more accessible sites for the physisorption of electrolyte ions and increasing the ionic conductivity at the electrode/electrolyte interface. In the procedure proposed by Wang and co-workers [62], the specific capacitance was increased from 28 F g−1 for raw CNTs to 85 F g−1 for CNTs-T in H2SO4 solution. Changing the electrolyte to H2SO4/hydroquinone mixture provides a drastic improvement of the specific capacitance to 508 and 3199 F g−1 for CNTs and CNTs-T, respectively [62].
The distribution and type of oxygen-containing functional groups depend on the type (Figure 7a) and concentration (Figure 7b) of the oxidizing agent [66, 67].
The oxidation of CNTs is a principle reaction for further functionalization of the carbon network. The combination of CNTs with graphene oxide in a lamellar graphene-CNT structure, r[GO/CNT], shown in Figure 8 causes an increase in the electrolyte-accessible surface area due to the intercalation of CNTs between the stacked GO sheets with associated large electrochemical active sites, thus improving conductivity through the formation of a 3D network aided by CNTs. Such a covalently linked CNTs-graphene system exhibits capacitance performance much superior than that of other carbon-based electrodes [77].
The high specific capacitance of CNTs could also be obtained with the incorporation of heteroatoms such as N [61, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87], B [86, 87, 88, 89], P [86, 90], and F [91]. The type of defect created by the heteroatom influences the kind of conduction generated ranging from n-type transport (N substitution doping) to p-type conduction (B substitution of boron in lattice) [92]. The existence of heteroatoms significantly enhances the specific capacitance values of carbon materials by the pseudocapacitance effect [83, 88]. Gueon and co-workers found that nitrogen-doped carbon nanotubes have a specific capacitance three times higher compared to undoped carbon nanomaterial [79]. Nitrogen-containing pentagons (Figure 9) can induce strong bending of the nanotubes and affect the alignment of the CNT lattice, resulting in the creation of donor states near the Fermi level and hence the specific capacitance [79, 80]. The effect of B-doping on the capacitance can be explained by modification of the space charge layer in carbon. The presence of boron leads to the enhancement of the space-charge layer capacitance through increasing the number of holes as a charge carrier or the DOS change at the Fermi level [88].
Thermal oxidation [88] or acid treatment [81] of doped CNTs improves the specific surface area and, as a consequence, the capacitance due to the tube end opening process. Coaxial supercapacitors based on hollow carbon nanotubes synthesized by chemical vapor deposition (CVD) exhibit high rate capacitance, long cycle life, and good flexibility [93].
The combination of synergetic effects in boron carbonitride nanotubes (BCNs) resulting from the combined co-doping of B and N in CNTs and their well-aligned vertical structure (VA) also provides a significant enhancement of specific capacitance performance. Vertically aligned boron carbonitride nanotubes (VA-BCNs) were synthesized on a Ni-Fe-coated SiO2/Si substrate using the chemical vapor deposition method with a melamine diborate precursor. In this case, nitrogen atoms are bonded to carbons in both graphitic and pyridinic forms, and the resultant VA-BCNs show high specific capacitance (321 F g−1) with an excellent rate capability and high durability compared to nonaligned BCNs (167 F g−1) and undoped multi-walled carbon nanotubes (117 F g−1) [94].
5. Hybrid materials of carbon nanotubes for energy storage
Carbon nanotubes are combined with carbon nanostructures, conducting polymers or metal oxides to form nanocomposite materials that display favorable electronic and mechanical properties [95]. Composites containing carbon nanotubes and an electroactive phase exhibit pseudocapacitive properties like metal oxide or conducting polymers and represent an important breakthrough for developing a new generation of supercapacitors based on three reasons: (i) the percolation of the electroactive particles is more efficient with nanotubes than with other carbon materials; (ii) the open mesoporous network formed by the entanglement of nanotubes allows ions to diffuse easily to the active surface of the composite components; and (iii) since the nanotubular materials are characterized by a high resiliency, the composite electrodes can easily adapt to the volumetric changes during the charging/discharging process, which improves drastically the cycling performance [22]. However, capacitors fabricated from inorganic pseudocapacitive materials typically suffer from higher internal resistance and lower lifetimes. The combination of carbon nanotubes with other carbon nanostructures results in an enhancement of energy density and lowering of the internal resistance [96].
5.1. Capacitors based on carbon nanotubes and different carbon nanostructures
The continued technological progress has led to the miniaturization of electronic devices with large volumetric energy densities. Most fabricated micro-supercapacitors based on carbon nanostructures exhibit excellent rate capabilities and stability, but low volumetric energy density. In general, increased volumetric energy density is obtained by the application of porous conductive electrode materials with sufficiently high packing density. The most popular electrode material is graphene sheets because of their ultrahigh surface area and excellent conductivity as well as high mechanical and chemical stability. However, various interesting structures of graphene, such as one-dimensional fibers, two-dimensional films, and three-dimensional foams, in spite of high gravimetric capacitance exhibit poor volumetric performance due to strong intersheet π-π interactions, which, while increasing the packing density, do not allow high ion accessibility. To solve this problem, the synergistic effect of graphene and carbon nanotubes is utilized by the preparation of graphene-carbon nanotubes composites. In most cases, graphene oxide is used due to its hydrophilic character. However, its conductivity is low, and hence, it is doped by carbon nanotubes with very high conductivity [97]. Numerous synthesis methods have been used and a large family of hybrid composites based on graphene oxide and carbon nanotubes with the specific capacitance in the range of 120–222 F g−1 depending on the preparation procedure has been discovered [77, 98, 99, 100, 101, 102, 103, 104].
Ternary carbon composites containing carbon nanotubes, graphene, and activated carbon exhibit much better capacitance performance. Such systems have specific capacitances several times higher than those of their components (Figure 10a). The excellent electrochemical properties of ternary composites can be attributed to the high surface area and low equivalent series resistance, demonstrating that they improve the electrochemical performance for supercapacitor applications [97]. Among the multicomponent composites, a novel type of highly flexible and all-solid state supercapacitor utilizing hybrid aerogels exhibits promising properties (Figure 10b) [105].
Recently, much attention has been paid to 3D pillared vertically aligned carbon nanotubes (VACNTs)—graphene architectures with a controllable nanotube length (PL)/intertube distance (MIPD) as electrode materials for energy-related devices (Figure 11). Theoretical studies have indicated that 3D pillared architectures, consisting of parallel graphene layers supported by vertically aligned carbon nanotubes (VACNTs) in between, possess desirable out-of-plane transport and mechanical properties while maintaining the excellent properties of their building blocks [102].
An ultrafast compact capacitor based on free-standing, flexible, and highly conducting films consisting of stacked nanoporous graphene layers pillared with single-walled carbon nanotubes (SWCNTs) was obtained by Pham and co-workers [109]. Figure 12 shows the carbon nanotube (CNT)-bridged graphene 3D building blocks via the Coulombic interaction between positively charged CNTs grafted by cationic surfactants and negatively charged graphene oxide sheets, followed by KOH activation. Such a structure enhances the accessible surface area and allows for fast ion diffusion. Due to this unique 3D porous structure, a remarkable electrochemical performance with a maximum capacitance as high as 199 F g−1 was achieved [99].
The electrodeposition of nickel hydroxide on such hybrid nanostructures results in pseudocapacitance due to the Faradaic reaction associated with the Ni(OH)2 coating. The specific capacitance is increased from 110 F g−1 obtained for VACNT-graphene architectures to 1384 F g−1 for Ni(OH)2-coated VACNT graphene electrode [102].
Pristine carbon nanotubes usually provide unsatisfactory specific capacitance due to their relatively low surface area, which still needs to be enhanced. Composites containing hollow carbon nanospheres anchored to the surface of carbon nanotubes, CNT-HCS, (Figure 13) are synthesized via the hard template method following this trend. Disordered pores (~2 nm) observed in the shells of the carbon spheres facilitate the penetration of electrolyte ions and favor the rapid charge propagation during the charge/discharge process [106]. The electrochemical performance of capacitors based on the composites of carbon nanotubes and different carbon nanostructures are collected in Table 2.
Composite | Specific capacitance (F g−1) | Capacitance | Power density | Energy density | Capacitance retention | Reference |
---|---|---|---|---|---|---|
CNF/rGO/CNT | 252 | 216 mF cm−2 | 9.5 mW cm−2 | 28.4 mW cm−2 | 99.5% | [105] |
HCS/CNT | 201.5 | 30.1 F cm−3 | 11.8 kW kg−1 | 11.3 Wh kg−1 | 90% | [106] |
SWCNT/GO | – | 305 F cm−3 | 1.085 mW cm−3 | 6.3 mWh cm−3 | 93% | [98] |
SWCNT/GO | 199 | 211 mF cm−3 | 400 kW kg−1 | 110.6 Wh kg−1 | 98.2% | [99] |
GO/CNT/AC | 636 | – | 550 W kg−1 | 16 Wh kg−1 | 99.8% | [97] |
Graphene/CNT | – | 3.93 mF cm−3 | 115 W cm−3 | 2.42 mWh cm−3 | 86% | [107] |
SWCNT/CNH | 43 | – | 3.50 kW kg−1 | 6.03 Wh kg−1 | – | [96] |
5.2. Capacitors based on carbon nanotubes and conducting polymers
Composites of conducting polymers with carbon nanotubes are promising electrode materials as supercapacitors because of their good conductivity, high surface area, and excellent ability to store energy [7, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117]. The composites combine the large pseudocapacitance of conducting polymers with the fast charging/discharging double-layer capacitance and excellent mechanical properties of carbon nanotubes [118]. In Scheme 1, the properties of carbon nanostructures, conducting polymers, and the composite materials are compared.
CNTs/conducting polymer composites can be prepared by chemical [7, 13, 108, 113, 114, 118, 119, 120, 121] or electrochemical [14, 16, 95, 110, 111, 112, 115, 118, 119, 121] polymerization. This process can be carried out on pristine CNTs or CNTs modified with functional groups or heteroatoms as a non-covalent deposition polymeric layer onto the nanotubular surface or covalent functionalization of carbon walls by polymeric chains. In the case of covalent functionalization, two approaches can be used: first, when the monomer is attached to CNTs and, in the next step, when it is polymerized via chemical or electrochemical methods [122, 123], and second, in situ chemical polymerization in the presence of dopant and self-organizing agent [7, 124]. For noncovalently modified CNTs with polymers, several strategies have been developed. Currently, they involve physical mixing in solution, in situ polymerization of monomers in the presence of CNTs, surfactant- and template-assisted processing of composites, chemical functionalization of the incorporated nanotubular material, and electrochemical polymerization carried out on an electrode surface modified with carbon nanostructures or electrochemical co-polymerization [118, 125, 126]. In Figure 14, exemplary procedures of nanocomposites formation are schematically presented. In most cases, electrochemical synthesis provides homogenous films [16, 118]. However, chemical polymerization generates polymers with a more porous morphology [118, 127].
Figure 15 shows the SEM images of SWCNTs/PPy composites prepared by deposition of PPy on pristine SWCNTs (Figure 15a) and on functionalized SWCNTs (Figure 15b). In the case of functionalized SWCNTs, an incomplete coverage of SWCNTs by PPy is observed [14].
A comparison of the electrochemical behavior of PPy, SWCNTs/PPy, and PPy/functionalized SWCNTs composites is shown in Figure 16. PPy films at a low scan rate exhibits a rectangular shape, which indicates an ideal capacitance behavior, while for higher scan rates, the curves are not rectangle-shaped, which indicates resistance-like electrochemical behavior due to the slow doping/dedoping process of the compact PPy layer. However, a pseudorectangular shape of the recorded cyclic voltammograms in all of the scan rates (up to 200 mV·s-1) is observed for the composites based on pristine SWCNTs (Figure 16b) and functionalized SWCNTs (Figure 16c). The PPy/functionalized SWCNTs composite exhibits also better capacitance properties compared to PPy/SWCNTs and pristine PPy (Figure 17).
Another way to form composites based on CNTs and conducting polymers is covalent functionalization of CNTs with monomeric units. In the next step, the composite is obtained by copolymerization of the monomer with monomer units grafted on the CNTs surface using controlled potential electrolysis. Figure 18a shows the electrochemical behavior of polypyrrole/CNTs (PPY/CNTs) composites obtained at different charge densities. The broad peaks observed in the voltammograms are related to the redox process within the polypyrrole component. The composites exhibit higher currents than the pure polymeric material due to higher porosity (Figure 18c) compared to pristine PPy (Figure 18b) and as a consequence of the higher capacitance of PPy/CNTs [122].
The presence of CNT components results in an increase in the practical range of electrical conductivity of the material. For example, C60-Pd polymer demonstrates pseudocapacitance behavior due to faradaic reduction of C60 in the negative potential range (Figure 19a); at potentials lower than this threshold, the material exhibits very high resistance. In the CNTs/C60Pd composite, the potential range of electrochemical activity increases. At negative potentials, the pseudocapacitive behavior of the polymeric component is still observed. However, the material also shows double-layer capacitance, mainly attributed to the conducting CNTs, in a less negative potential range (Figure 19b). Composites based on C60-Pd polymers and SWCNTs or MWCNTs exhibit specific capacitance equal to 994 F g−1 or 758 F g−1 for SWCNTs/ C60-Pd and MWCNTs/C60-Pd composites, respectively [119].
A very promising energy storage behavior was reported for 3D structure composite based on aligned carbon nanotubes (ACNTs) offering a large specific surface area, superior electronic transfer ability through individual nanotubes, and chemical inertness [95]. Three-dimensional hybrid composite material composed of 2D fish scale-like polyaniline nanosheet arrays on graphene oxide sheets and carbon nanotubes exhibiting high specific capacitance of 589 F g−1 compared to 397 F g−1 for pristine PANI was also investigated [18]. Moreover, ternary composite systems containing carbon nanotubes, graphene, and conducting polymers were also investigated [128, 131]. The capacitance properties of selected composites of carbon nanotubes and conducting polymers are reported in Table 3.
Carbon nanostructure | Composite | Specific capacitance (F g−1) | Reference |
---|---|---|---|
SWCNT | SWCNT/PPy | 200 | [14] |
SWCNT/PPy | 305 | [132] | |
SWCNT/PANI | 247 | [129] | |
SWCNT/PANI | 485 | [111] | |
SWCNT/PANI | 707 | [133] | |
SWCNT/PANI | 1000 | [134] | |
SWCNT/C60-Pd | 994 | [119] | |
MWCNT | MWCNT/PANI | 50 | [120] |
MWCNT/PANI | 500 | [112] | |
MWCNT/PANI | 670 | [130] | |
MWCNT/PPy | 70 | [120] | |
MWCNT/PPy | 268 | [7] | |
MWCNT/PPy | 243 | [16] | |
MWCNT/PPy | 506 | [130] | |
MWCNT/PPy | 554 | [126] | |
MWCNT/C60-Pd | 758 | [119] | |
MWCNT/PEDOT:PSS | 30 | [120] | |
MWCNT/PEDOT | 237 | [126] | |
Graphene/CNT | Graphene/CNT/PPy | 453 | [132] |
GO/CNT | GO/CNT/PANI | 413 | [18] |
5.3. Composites containing carbon nanotubes and metal oxides
To overcome the low energy density of supercapacitors, pseudocapacitors based on transition metal oxides have been developed [135]. The most promising among them is manganese dioxide MnO2 because of its low cost, environmental compatibility, natural abundance, high energy density, and excellent capacitive performance in aqueous electrolytes [32, 135, 136, 137, 138, 139, 140, 141, 142, 143]. In aqueous electrolytes, the charging mechanism of MnO2 may be described by the following reaction:
where M represents protons (H+) and/or alkali cations such as K+, Na+, and Li+. The charge storage is based either on the adsorption of cations at the surface of the electrode material or on the intercalation of cations in the bulk of the electrode material. However, the reported specific capacitance values for the various structures of MnO2 electrodes are still far from the theoretical one [144], which may be attributed to the intrinsically poor electronic conductivity of MnO2. To improve the capacitive performance of MnO2, composites with carbon nanotubes characterized by high conductivity and high surface area are formed [143]. The surface morphology of CNTs/MnO2 composite and its components is shown in Figure 20. Figure 21a shows the comparison of the specific capacitances of pristine CNTs, pure MnO2 and a composite where CNTs are decorated by MnO2 nanoflakes. CNTs exhibit the best rate capability, but their capacitance is the lowest due to the charge storage mechanism typical for double layer capacitors. The low rate capability of MnO2 is associated with its poor electronic conductivity and low specific surface area. The combination of MnO2 and CNTs provides the formation of a MnO2/CNT nanocomposite exhibiting good rate capability and high specific capacitance. The results obtained by electrochemical impedance spectroscopy (Figure 21b) show that the MnO2/CNT composite has a much lower diffusive resistance compared to pure MnO2 because the slope of the low-frequency straight line representing the diffusive resistance of electrolyte in the electrode pores and cation diffusion in the host materials is similar to the line obtained for the CNTs but much larger than that of the pure MnO2. Additionally, the charge transfer resistance,
Apart from MnO2 [9, 17, 135, 136, 143, 145, 146, 147, 148, 149, 150], other metal oxides such as hydrous RuO2 [151, 152, 153, 154], NiO [155, 156], Fe2O3 [157], Co3O4 [158], MoO3 [10, 135, 159], V2O5 [160], CeO2 [161], and NiCo2O4 [162], In2O3 [149], TiO2 [153], SnO2 [153], and (Sn + Mn)Ox [163] are also utilized for the formation of composite electrodes. In the case of the expensive hydrous ruthenium oxide (RuO2·
So far, most studies have been devoted to the deposition of the pseudocapacitance phase onto carbon nanostructures. However, it is also possible to encapsulate metal oxides with CNTs. The MnO2@CNTs material exhibits a significantly higher specific capacitance compared to MnO2 outside of carbon nanotubes (Table 4). The difference in the electrochemical behaviors of MnO2 enclosed in CNTs (MnO2-
Carbon nanostructure | Composite | Specific capacitance (F g−1) | Reference |
---|---|---|---|
SWCNT | SWCNT/In2O3 | 201 | [149] |
SWCNT/MnO2 | 253 | [149] | |
SWCNT/NiC2O4 | 1642 | [162] | |
MWCNT | MWCNT/MoO3 | 70 | [159] |
MWCNT/MoO3 | 178 | [10] | |
MWCNT/MnO2 | 250 | [147] | |
MWCNT/MnO2 | 944 | [145] | |
MWCNT/RuO2 | 138 | [153] | |
MWCNT/RuO2 | 953 | [151] | |
MWCNT/RuO2 | 1050 | [154] | |
MWCNT/SnO2 | 93 | [153] | |
MWCNT/NiO | 160 | [155] | |
MWCNT/NiO | 523 | [156] | |
MWCNT/TiO2 | 160 | [153] | |
MWCNT/Co3O4 | 201 | [158] | |
MWCNT/(Sn+Mn)Ox | 337 | [163] | |
MWCNT/MC/MnO2 | 351 | [165] | |
MWCNT@MnO2@PPy | 273 | [12] | |
CNT | MnO2- |
790 | [9] |
MnO2- |
1250 | [9] | |
CNT/MnO2 | 199 | [150] | |
CNT/MnO2 | 214 | [148] |
The oxidation potential of MnO2-
Moreover, hybrid materials such as carbon nanotubes/mesoporous carbon/MnO2 [165], carbon nanotubes/3D graphene/MnO2 [11], and carbon nanotube@MnO2@polypyrrole [12] have been developed. Table 4 shows the capacitance of exemplary composites based on carbon nanostructures and metal oxides.
5.4. Capacitors based on carbon nanotubes and carbon gels
Recently, much attention has been paid to novel ultralight mesoporous carbon materials named carbon aerogels (CAGs) [15, 166, 167, 168, 169, 170, 171, 172, 173] or carbon xerogels [8, 174, 175, 176, 177, 178]. Carbon aerogels exhibit many interesting properties such as low mass density, continuous porosity, high surface area, and high electrical conductivity. These properties are characteristic of the aerogel microstructure, which is a network of interconnected primary particles with diameters between 3 and 25 nm (Figure 23a). However, aerogels consist of agglomerate particles linked by covalent bridges with a ladder structure. The contact between these particles and the space due to the pores unfortunately introduces a high internal resistance within the aerogel which limits their practical applications. To overcome this problem, composites of carbon aerogels with carbon nanotubes are formed (Figure 23b). CNTs with their high electrical conductivity work as nanopathways for charges and thus improve the intrinsic conductivity of the CAGs and their mechanical integrity as well [166].
The main problem in the case of composite formation is the agglomeration of carbon nanotubes within the CAG’s pore network. A very useful approach for the formation of binderless carbon nanotube aerogel (CNAG) composites proposed by Bordjiba and co-workers [166, 172] provides a significant improvement in the dispersion of carbon nanotubes within the aerogel matrix and better interfacial coating. The CNAG material was prepared by a molding procedure, i.e., synthesis by a chemical vapor deposition method to grow carbon nanotubes directly onto a microfibrous carbon paper substrate. In the next step, the carbon aerogel was synthesized on the carbon nanotubes. The key feature of this method is eliminating the need to control the carbon nanotube concentration, which permits optimized dispersion processes to reinforce the aerogel’s networks. The CNAG electrode delivered very high specific capacitances equal to 524 F g−1. Furthermore, better integration of carbon nanotubes in the matrix of carbon aerogel improves its resistance to attack by the electrolyte and assures excellent cycle life. Such a system exhibits significantly higher capacitance and stability compared to the composite processed from the dispersion of its components in liquid phase, CAG-3%MWNT (Figure 24). Apart from the capacitance performance, binderless nanostructured electrodes also reduce the cost of manufacturing and avoid complicated interferences of the binders and conductivity enhancers used in practical electrodes [166, 172].
The research on CNTs and carbon aerogel composites is relatively new because their very promising properties are still being developed. The composites that have been prepared so far exhibit excellent capacitance properties [8, 166, 170, 171, 172, 177, 178]. A large progress in this area of study can be expected in the near future.
6. Conclusion and outlook
Supercapacitors have been developed to close the gap between conventional capacitors and batteries because of their high energy density and power density. In the development of electrochemical capacitors, carbon nanotubes and their composites have been widely used as electrode materials. The specific capacitance of pristine carbon nanotubes is relatively low and depends on many factors such as the kind of carbon nanotubular material, i.e., single- or multi-walled, its orientation, i.e., open or closed tips, surface area, synthesis method, solvent and supporting electrolyte. Compared with pristine carbon nanotubes, functionalized carbon nanotubes by heteroatoms or functional groups attached to nanotubes walls are expected to display improved capacitance performance. The formation of composites based on carbon nanotubes provides especially high surface area due to the presence of CNTs which is very important in the case of storage systems. Moreover, it enhances the properties of both the carbon nanotubes and the second component. Apart from the improvement in capacitance performance, the addition of CNTs reduces cost compared to metal oxide, improves stability compared to conducting polymers which exhibit rapid degradation in performance after repetitive cycles because of their swelling and shrinking, and improves the poor volumetric performance of supercapacitors based on other carbon nanomaterials. The capacitance properties strongly depend on the localization of the redox system. It was found that encapsulation of the redox phase inside a nanotubular material provides higher specific capacitance compared to a redox system situated outside of carbon nanotubes. Recently, a new generation of cheap storage systems based on mesoporous carbon aerogels was discovered. However, in this case, there is a problem with the non-homogeneous spread of carbon nanotubes within the whole network of carbon aerogel. Hence, increasing attention is needed to solve this problem because this system could be the future for storage devices. A very promising system seems to be the attachment of redox-active nanoparticles to carbon nanotubes. Compared to bulk materials, they exhibit unique properties arising from their nanoscale sizes, such as high electrical conductivity, large surface area, short path lengths for the transport of ions and high electrochemical activity. Ultrafast compact capacitors based on 3D hybrid structures that increase the accessible surface area and allow fast ion diffusion are introducing a new class of electrode materials for storage devices. A comparison of the properties of composites based on carbon nanotubes and their components is summarized in Scheme 2.
Acknowledgments
The authors acknowledge the National Center of Science (project No. 2016/21/B/ST5/02496 to KW) for a financial support.
References
- 1.
Kandalkar SG, Gunjakar JL, Lokhande CD. Preparation of cobalt oxide thin films and its use in supercapacitor application. Applied Surface Science. 2008; 254 :5540-5544. DOI: 10.1016/j.apsusc.2008.02.163 - 2.
Chen GZ. Supercapacitor and supercapattery as emerging electrochemical energy stores. International Materials Reviews. 2017; 62 :173-202. DOI: 10.1080/09506608.2016.1240914 - 3.
Garcia P, Torreglosa JP, Fernandez LM, Jurado F. Control strategies for high-power electric vehicles powered by hydrogen fuel cell, battery and supercapacitor. Expert Systems with Applications. 2013; 40 :4791-4804. DOI: 10.1016/j.eswa.2013.02.028 - 4.
Li J, Cheng X, Sashurin A, Keidar M. Review of electrochemical capacitors based on carbon nanotubes and graphene. Graphene. 2012; 1 :1-13. DOI: 10.4236/graphene.2012.11001 - 5.
Du R, Zhao Q, Zhang N, Zhang J. Marcoscopic carbon nanotube-based 3D monoliths. Small. 2015; 11 :3263-3289. DOI: 10.1002/smll.201403170 - 6.
In JB, Grigoropoulos CP, Chernov AA, Noy A. Growth kinetics of vertically aligned carbon nanotube arrays in clean oxygen-free conditions. ACS Nano. 2011; 5 :9602-9610. DOI: 10.1021/nn2028715 - 7.
Reddy RK, Alonso-Marroquin F. Polypyrrole functionalized with carbon nanotubes as an efficient and new electrodes for electrochemical supercapacitors. AIP Conference Proceedings. 2017; 1856 :020002-1-020002-4. DOI: 10.1063/1.4985553 - 8.
Fathy NA, Annamalai KP, Tao Y. Effects of phosphoric acid activation on the nanopore structures of carbon xerogel/carbon nanotubes hybrids and their capacitance storage. Adsorption. 2017; 23 :355-360. DOI: 10.1007/s10450-017-9860-y - 9.
Chen W, Fan Z, Gu L, Bao X, Wang C. Enhanced capacitance of manganese oxide via confinement inside carbon nanotubes. Chemical Communication. 2010; 46 :3905-3907. DOI: 10.1039/c000517g - 10.
Shakir I, Sarfraz M. Evaluation of electrochemical charge storage mechanism and structural changes in interwined MoO3-MWCNTs composites for supercapacitor applications. Electrochimica Acta. 2014; 147 :380-384. DOI: 10.1016/j.electacta.2014.09.073 - 11.
Pan Z, Liu M, Yang J, Qiu Y, Li W, Xu Y, Zhang X, Zhang Y. High electroactive material loading on a carbon nanotube@graphene aerogel for high-performance flexible all-solid-state asymmetric supercapacitors. Advanced Functional Materials. DOI: 10.1002/adfm.201701122 - 12.
Pequeno de Oliveira AH, Ferreira Nascimento ML, Pequeno de Oliveira H. Carbon nanotube@MnO2@polypyrrole composites: Chemical synthesis, characterization and application in supercapacitors. Materials Research. 2016; 19 (5):1080-1087. DOI: 10.1590/1980-5373-MR-2016-0347 - 13.
Mi H, Zhang X, Xu Y, Xiao F. Synthesis, characterization and electrochemical behavior of polypyrrole/carbon nanotube composites using organometallic-functionalized carbon nanotubes. Applied Surface Science. 2010; 256 :2284-2288. DOI: 10.1016/j.apsusc.2009.10.053 - 14.
Wang J, Xu Y, Chen X, Sun X. Capacitance properties of single wall carbon nanotube/polypyrrole composite films. Composites Science and Technology. 2007; 67 :2981-2985. DOI: 10.1016/j.compscitech.2007.05.015 - 15.
Worsley MA, Satcher JH, Baumann T. Synthesis and characterization of monolithic carbon aerogel nanocomposites containing double-walled carbon nanotubes. Langmuir. 2008; 24 :9763-9766. DOI: 10.1021/la8011684 - 16.
Sun X, Xu Y, Wang J, Mao S. The composite film of polypyrrole and functionalized multi-walled carbon nanotubes as an electrode material for supercapacitors. International Journal of Electrochemical Science. 2012; 7 :3205-3214 - 17.
Cheng Q, Ma J, Zhang H, Shinya N, Qin LC, Tang J. Electrodeposition of MnO2 on carbon nanotube thin films as flexible electrodes for supercapacitors. Transactions of the Materials Research Society of Japan. 2010; 35 (2):369-372 - 18.
Ning G, Li T, Yan J, Xu C, Wei T, Fan Z. Three-dimensional hybrid materials of fish scale-like polyaniline nanosheet arrays on graphene oxide and carbon nanotube for high-performance ultracapacitors. Carbon. 2013; 54 :241-248. DOI: 10.1016/j.carbon.2012.11.035 - 19.
Kotz R, Carlen M. Principles and applications of electrochemical capacitors. Electrochimica Acta. 2000; 45 :2483-2498. DOI: 10.1016/S0013-4686(00)00354-6 - 20.
Zhang Y, Feng H, Wu X, Wang L, Zhang A, Xia T, Dong H, Li X, Zhang L. Progress of electrochemical capacitor electrode materials: A review. International Journal of Hydrogen Energy. 2009; 34 :4889-4899. DOI: 10.1016/j.ijhydene.2009.04.005 - 21.
Yamada H, Bandaru PR. Limits to the magnitude of capacitance in carbon nanotube array electrode based electrochemical capacitors. Applied Physics Letters. 2013; 102 :173113-1-173113-4. DOI: 10.1063/1.4803925 - 22.
Pan H, Li J, Feng YP. Carbon nanotubes for supercapacitor. Nanoscale Research Letters. 2010; 5 :654-668. DOI: 10.1007/s11671-009-9508-2 - 23.
Forse AC, Merlet C, Griffin JM, Grey CP. New perspectives on the charging mechanisms of supercapacitors. Journal of the American Chemical Society. 2016; 138 :5731-5744. DOI: 10.1021/jacs.6b02115 - 24.
Karden E, Ploumen S, Fricke B, Miller T, Snyder K. Energy storage devices for future hybrid electric vehicles. Journal of Power Sources. 2007; 168 :2-11. DOI: 10.1016/j.jpowsour.2006.10.090 - 25.
Thounthong P, Rael S, Davat B. Control strategy of fuel cell/supercapacitors hybrid power sources for electric vehicle. Journal of Power Sources. 2006; 158 :806-814. DOI: 10.1016/j.jpowsour.2005.09.014 - 26.
Ghosh S, Inganas O. Conducting polymers hydrogels as 3D electrodes: Applications for supercapacitors. Advanced Materials. 1999; 11 :1214-1218. DOI: 10.1002/(SICI)1521-4095(199910)11:14<1214::AID-ADMA1214>3.0.CO;2-3 - 27.
Fic K, Lota G, Meller M, Frackowiak E. Novel insight into neutral medium as electrolyte for high-voltage supercapacitors. Energy & Environmental Science. 2012; 5 :5842-5850. DOI: 10.1039/c1ee02262h - 28.
Reddy ALM, Amitha FE, Jafri I, Ramaprabhu S. Asymmetric flexible supercapacitor stack. Nanoscale Research Letters. 2008; 3 :145-151. DOI: 10.1007/s11671-008-9127-3 - 29.
Chen T, Dai L. Carbon nanomaterials for high-performance supercapacitors. Materials Today. 2013; 16 :272-280. DOI: 10.1016/j.mattod.2013.07.002 - 30.
Zhang LL, Zhao XS. Carbon-based materials as supercapacitor electrodes. Chemical Society Reviews. 2009; 38 :2520-2531. DOI: 10.1039/b813846j - 31.
Zhang LL, Zhou R, Zhao XS. Graphene-based materials as supercapacitor electrodes. Journal of Materials Chemistry. 2010; 20 :5983-5992. DOI: 10.1039/c000417k - 32.
Shi F, Li L, Wang XL, Gu CD, Tu JP. Metal oxide/hydroxide-based materials for supercapacitors. RSC Advances. 2014; 4 :41910-41921. DOI: 10.1039/c4ra06136e - 33.
Lu W, Qu L, Henry K, Dai L. High performance electrochemical capacitors from aligned carbon nanotube electrodes and ionic liquid electrolytes. Journal of Power Sources. 2009; 189 :1270-1277. DOI: 10.1016/j.jpowsour.2009.01.009 - 34.
Huang J, Sumpter BG, Meunier V. A universal model for nanoporous carbon supercapacitors applicable to diverse pore regimes, carbon materials, and electrolytes. Chemistry A European Journal. 2008; 14 :6614-6626. DOI: 10.1002/chem.200800639 - 35.
Barisci JN, Wallace GG, Baughman RH. Electrochemical studies of single-wall carbon nanotubes in aqueous solutions. Journal of Electroanalytical Chemistry. 2000; 488 :92-98. DOI: 10.1016/S0022-0728(00)00179-0 - 36.
Li J, Cassell A, Delzeit L, Meyyappan M. Novel three-dimensional electrodes: Electrochemical properties of carbon nanotube ensembles. Journal of Physical Chemistry B. 2002; 106 :9299-9305. DOI: 10.1021/jp021201n - 37.
Pumera M. Electrochemical properties of double wall carbon nanotube electrodes. Nanoscale Research Letters. 2007; 2 :87-93. DOI: 10.1007/s11671-006-9035-3 - 38.
Frackowiak E, Jurewicz K, Delpeux S, Beguin F. Nanotubular materials for supercapacitors. Journal of Power Sources. 2001; 97-98 :822-825. DOI: 10.1016/S0378-7753(01)00736-4 - 39.
Krivenko AG, Matyushenko VI, Stenina EV, Sviridova LN, Krestinin AV, Zvareva GI, Kurmaz VA, Ryabenko AG, Dmitriev SN, Skuratov VA. Peculiarities of the electrochemical behavior of modified electrodes containing single-wall carbon nanotubes. Elecrochemistry Communications. 2005; 7 :199-204. DOI: 10.1016/j.elecom.2004.12.009 - 40.
Oh J, Kozlov ME, Kim BG, Kim H-K, Baughman RH, Hwang YH. Preparation and electrochemical characterization of porous SWNT–PPy nanocomposite sheets for supercapacitor applications. Synthetic Metals. 2008; 158 :638-641. DOI: 10.1016/j.synthmet.2008.04.007 - 41.
Liu CG, Fang HT, Li F, Liu M, Cheng HM. Single-walled carbon nanotubes modified by electrochemical treatment for application in electrochemical capacitors. Journal of Power Sources. 2006; 160 :758-761. DOI: 10.1016/j.jpowsour.2006.01.072 - 42.
Vivekchand SRC, Rout CS, Subrahmanyam KS, Govindaraj A, Rao CNR. Graphene-based electrochemical supercapacitors. Journal of Chemical Sciences. 2008; 120 :9-13. DOI: 10.1007/s12039-008-0002-7 - 43.
Jurewicz K, Babeł K, Pietrzak R, Delpeux S, Wachowska H. Capacitance properties of multi-walled carbon nanotubes modified by activation and ammoxidation. Carbon. 2006; 44 :2638-2375. DOI: 10.1016/j.carbon.2006.05.044 - 44.
Deng L, Hao Z, Wang J, Zhu G, Kang L, Liu Z-H, Yang Z, Wang Z. Preparation and capacitance of graphene/multiwall carbon nanotubes/MnO2 hybrid material for high-performance asymmetrical electrochemical capacitor. Electrochimica Acta. 2013; 89 :191-198. DOI: 10.1016/j.electacta.2012.10.106 - 45.
Valentini L, Armentano I, Kenny JM. Sensors for sub-ppm NO2 gas detection based on carbon nanotube thin films. Applied Physics Letters. 2003; 82 :961-963. DOI: 10.1063/1.1545166 - 46.
Rueckes T, Kim K, Joselevich E, Tseng GY, Cheung C-L, Lieber CM. Carbon nanotube—Based nonvolatile random access memory for molecular computing. Science. 2000; 289 :94-97. DOI: 10.1126/science.289.5476.94 - 47.
Martel R, Schmidt T, Shea HR, Hertel T, Avouris P. Single- and multi-wall carbon nanotube field-effect transistors. Applied Physics Letters. 1998; 73 :2447-2449. DOI: 10.1063/1.122477 - 48.
Kamat PV, Thomas KG, Barazzouk S, Girishkumar G, Vinodgopal MD. Self-assembled linear bundles of single wall carbon nanotubes and their alignment and deposition as a film in a dc field. Journal of the American Chemical Society. 2004; 126 :10757-10762. DOI: 10.1021/ja0479888 - 49.
Xin H, Woolley AT. Directional orientation of carbon nanotubes on surfaces using a gas flow cell. Nano Letters. 2004; 4 :1481-1484. DOI: 10.1021/nl049192c - 50.
Wang D, Song P, Liu C, Wu W, Fan S. Highly oriented carbon nanotube papers made of aligned carbon nanotubes. Nanotechnology. 2008; 19 :1-6. DOI: 10.1088/0957-4484/19/7/075609 - 51.
Wang Y, Iqbal Z. Vertically oriented single-wall carbon nanotube/enzyme on silicon as biosensor electrode. JOM. 2005; 34 :27-29. DOI: 10.1007/s11837-005-0132-z - 52.
Cao A, Ajayan PM, Ramanath G, Baskaran R, Turner K. Silicon oxide thickness-dependent growth of carbon nanotubes. Applied Physics Letters. 2004; 84 :109-111. DOI: 10.1063/1.1636826 - 53.
Liu Z, Shen Z, Zhu T, Hou S, Ying L. Organizing single-walled carbon nanotubes on gold using a wet chemical self-assembling technique. Langmuir. 2000; 16 :3569-3573. DOI: 10.1021/la9914110 - 54.
Taurino I, Carrara S, Giorcelli M, Tagliaferro A, De Micheli G. Comparison of two different carbon nanotube-based surfaces with respect to potassium ferricyanide electrochemistry. Surface Science. 2012; 606 :156-160. DOI: 10.1016/j.susc.2011.09.001 - 55.
Azam MA, Fujiwara A, Shimoda T. Significant capacitance performance of vertically aligned single-walled carbon nanotube supercapacitor by varying potassium hydroxide concentration. International Journal of Electrochemical Science. 2013; 8 :3902-3911 - 56.
Luo Y, Li X, Gong Z, Sheng Z, Peng X, Mou Q, He M, Li X, Chen H. Aligned carbon nanotubes array by DC glow plasma etching for supercapacitor. Journal of Nanomaterials. DOI: 10.1155/2013/270289 - 57.
Izadi-Najafabadi A, Futaba DN, Iijima S, Hata K. Ion diffusion and electrochemical capacitance in aligned and packed single-walled carbon nanotubes. Journal of the American Chemical Society. 2010; 132 :18017-18019. DOI: 10.1021/ja108766y - 58.
Park SK, Mahmood Q, Park HS. Surface functional groups of carbon nanotubes to manipulate capacitive behaviors. Nanoscale. 2013; 5 :12304-12309. DOI: 10.1039/c3nr04858f - 59.
Balasubramanian K, Burghard M. Electrochemically functionalized carbon nanotubes for device applications. Journal of Materials Chemistry. 2008; 18 :3071-3083. DOI: 10.1039/b718262g - 60.
Tasis D, Tagmatachris N, Bianco A, Prato M. Chemistry of carbon nanotubes. Chemical Reviews. 2006; 106 :1105-1136. DOI: 10.1021/cr050569o - 61.
Zhou Z, Zhang Z, Peng H, Qin Y, Li G, Chen K. Nitrogen- and oxygen-containing activated carbon nanotubes with improved capacitive properties. RSC Advances. 2014; 4 :5524-5530. DOI: 10.1039/c3ra45076g - 62.
Wang G, Liang R, Liu L, Zhong B. Improving the specific capacitance of carbon nanotubes-based supercapacitors by combining introducing functional groups on carbon nanotubes with using redox-active electrolyte. Electrochimica Acta. 2014; 115 :183-188. DOI: 10.1016/j.electacta.2013.10.165 - 63.
Mombeshora ET, Ndungu PG, Jarvis ALL, Nyamori VO. Oxygen-modified multiwalled carbon nanotubes: Physicochemical properties and capacitor functionality. International Journal of Energy Research. 2017; 41 :1182-1201. DOI: 10.1002/er.3702 - 64.
Tian Y, Amal R, Wang D-W. An aqueous metal-ion capacitor with oxidized carbon nanotubes and metallic zinc electrodes. Frontiers in Energy Research. 2016; 4 :1-14. DOI: 10.3389/fenrg.2016.00034 - 65.
Smith B, Wepasnick K, Schrote KE, Bertele AR, Ball WP, O’melia C, Fairbrother DH. Colloidal properties of aqueous of acid-treated multi-walled carbon nanotubes. Environmental Science & Technology. 2009; 43 :819-825. DOI: 10.1021/es802011e - 66.
Wepasnick KA, Smith BA, Schrote KE, Wilson KH, Diegelmann SR, Fairbrother DH. Surface and structural characterization of multi-walled carbon nanotubes following different oxidative treatments. Carbon. 2011; 49 :24-36. DOI: 10.1016/j.carbon.2010.08.034 - 67.
Wepasnick KA, Smith BA, Botter JL, Fairbrother DH. Chemical and structural characterization of carbon nanotube surfaces. Analytical and Bioanalytical Chemistry. 2010; 396 :1003-1014. DOI: 10.1007/s00216-009-3332-5 - 68.
Smith B, Wepasnick K, Schrote KE, Cho H-H, Ball WP, Fairbrother DH. Influence of surface oxides on the colloidal stability of multi-walled carbon nanotubes: A structure-property relationship. Langmuir. 2009; 25 (17):9767-9776. DOI: 10.1021/la901128k - 69.
Datsyuk V, Kaylva M, Papagelis K, Parthenios J, Tasis D, Siokou A, Kallitsis I, Galiotis C. Chemical oxidation of multiwalled carbon nanotubes. Carbon. 2008; 46 :833-840. DOI: 10.1016/j.carbon.2008.02.012 - 70.
Li M, Boggs M, Beebe TP, Huang CP. Oxidation of single-walled carbon nanotubes in dilute aqueous solutions by ozone as affected by ultrasound. Carbon. 2008; 46 :466-475. DOI: 10.1016/j.carbon.2007.12.012 - 71.
Komarova NS, Krivenko AG, Stenina EV, Sviridova LN, Mironovich KV, Shulga YM, Krivchenko VA. Enhancement of the carbon nanowall film capacitance. Electron transfer kinetics on functionalized surfaces. Langmuir. 2015; 31 :7129-7137. DOI: 10.1021/acs.langmuir.5b00391 - 72.
Ye JS, Liu X, Cui HF, Zhang W-D, Sheu F-S, Lim TM. Electrochemical oxidation of multi-walled carbon nanotubes and its application to electrochemical double layer capacitors. Electrochemistry Comunications. 2005; 7 :249-255. DOI: 10.1016/j.elecom.2005.01.008 - 73.
Jang IY, Lee SH, Park KC, Wongwiriyapan W, Kim C, Teshima K, Oishi S, Kim YJ, Endo M. Effect of photochemically oxidized carbon nanotubes on the deposition of platinum nanoparticles for fuel cells. Electrochemistry Comunications. 2009; 11 :1472-1475. DOI: 10.1016/j.elecom.2009.05.036 - 74.
Lee SH, Jung YC, Kim YA, Muramatsu H, Teshima K, Oishi S, Endo M. Optical spectroscopic studies of photochemically oxidized single-walled carbon nanotubes. Nanotechnology. 2009; 20 :1-5. DOI: 10.1088/0957-4484/20/10/105708 - 75.
Zschoerper NP, Kotzenamier V, Vohrer U, Haupt M, Oehr C, Hirth T. Analytical investigation of the composition of plasma-induced functional groups on carbon nanotube sheets. Carbon. 2009; 47 :2174-2185. DOI: 10.1016/j.carbon.2009.03.059 - 76.
Yang D-Q, Sacher E. Strongly enhanced interaction between evaporated Pt nanoparticles and functionalized multiwalled carbon nanotubes via plasma surface modifications: Effects of physical and chemical defects. Journal of Physical Chemistry C. 2008; 112 :4075-4082. DOI: 10.1021/jp076531s - 77.
Jung N, Kwon S, Lee D, Yoon D-M, Park YM, Benayad A, Choi J-Y, Park JS. Synthesis of chemically bonded graphene/carbon nanotube composites and their application in large volumetric capacitance supercapacitors. Advanced Materials. 2013; 25 :6854-6858. DOI: 10.1002/adma.201302788 - 78.
Xu D, Ding B, Nie P, Shen L, Wang J, Zhang X. Porous nitrogen-doped carbon nanotubes derived from tubular polypyrrole for energy-storage applications. Chemistry A European Journal. 2013; 19 :12306-12312. DOI: 10.1002/chem.201301352 - 79.
Gueon D, Moon JH. Nitrogen-doped carbon nanotube spherical particles for supercapacitor applications: Emulsion-assisted compact packing and capacitance enhancement. ACS Applied Materials & Interfaces. 2015; 7 :20083-20089. DOI: 10.1021/acsami.5b05231 - 80.
Karakaya M, Zhu J, Raghavendra AJ, Podila R, Parler SG, Kaplan JP, Rao AM. Roll-to-roll production of spray coated N-doped carbon nanotube electrodes for supercapacitors. Applied Physics Letters. 2014; 105 :263103-1-263103-4. DOI: 10.1063/1.4905153 - 81.
John AR, Arumugam P. Open ended nitrogen-doped carbon nanotubes for the electrochemical storage of energy in a supercapacitor electrode. Journal of Power Sources. 2015; 277 :387-392. DOI: 10.1016/j.jpowsour.2014.11.151 - 82.
Liao L, Pan C. Enhanced electrochemical capacitance of nitrogen-doped carbon nanotubes synthesized from amine flames. Soft Nanoscience Letters. 2011; 1 :16-23. DOI: 10.4236/snl.2011.11004 - 83.
Yun YS, Park HH, Jin H-J. Pseudocapacitive effects of N-doped carbon nanotube electrodes in supercapacitors. Materials. 2012; 5 :1258-1266. DOI: 10.3390/ma5071258 - 84.
Dubal DP, Chodankar NR, Caban-Huertas Z, Wolfart F, Vidotti M, Holze R, Lokhande CD, Gomez-Romero P. Synthetic approach from polypyrrole nanotubes to nitrogen doped pyrolyzed carbon nanotubes for asymmetric supercapacitors. Journal of Power Sources. 2016; 308 :158-165. DOI: 10.1016/j.jpowsour.2016.01.074 - 85.
Ayala P, Arenal R, Rummeli M, Rubio A, Pichler T. The doping of carbon nanotubes with nitrogen and their potential applications. Carbon. 2010; 48 :575-586. DOI: 10.1016/j.carbon.2009.10.009 - 86.
Mousavi-Khosedel SM, Jahanbakhsh-bonab P, Targholi E. Structural, electronic properties, and quantum capacitance of B, N and P-doped armchair carbon nanotubes. Physics Letters A. 2016; 380 :3378-3383. DOI: 10.1016/j.physleta.2016.07.067 - 87.
Terrones M, Souza Filho AG, Rao AM. Doped Carbon Nanotubes: Synthesis, Characterization and Applications. In: Jorio A, Dresselhaus G, Dresselhaus MS, editors. Topics in Applied Physics. Berlin, Heidelberg: Springer-Verlag Berlin Heidelberg; 2008. pp. 531-566. DOI: 10.1007/978-3-540-72865-8_17 - 88.
Siraishi S, Kibe M, Yokoyama T, Kurihara H, Patel N, Oya A, Kaburagi Y, Hishiyama Y. Electric double layer capacitance of multi-walled carbon nanotubes and B-doping effect. Applied Physics A. 2006; 82 :585-591. DOI: 10.1007/s00339-005-3399-6 - 89.
Yeh M-H, Lin L-Y, Li T-J, Leu Y-A, Chen G-L, Tien T-C, Hsieh C-Y, Lo S-C, Huang S-J, Chiang W-H, Ho K-C. Synthesis of boron-doped multi-walled carbon nanotubes by an ammonia-assisted substitution reaction for applying in supercapacitors. Energy Procedia. 2014; 61 :1764-1767. DOI: 10.1016/j.egypro.2014.12.207 - 90.
Patino J, Lopez-Salas N, Gutierrez MC, Carriazo D, Ferrer ML, del Monte F. Phosphorous-doped carbon-nanotube hierarchical monoliths as true three-dimensional electrodes in supercapacitor cells. Journal of Materials Chemistry A. 2016; 4 :1251-1263. DOI: 1039/C5TA09210H - 91.
Lee JY, An KH, Heo JK, Lee YH. Fabrication of supercapacitor electrodes using fluorinated single-walled carbon nanotubes. Journal of Physical Chemistry B. 2003; 107 :8812-8815. DOI: 10.1021/jp034546u - 92.
Majeed S, Zhao J, Zhang L, Anjum S, Liu Z, Xu G. Synthesis and electrochemical applications of nitrogen-doped carbon nanomaterials. Nanotechnology Reviews. 2013; 2 (6):615-635. DOI: 10.1515/ntrev-2013-0007 - 93.
Zang X, Xu R, Zhang Y, Li X, Zhang L, Wei J, Wang K, Zhu H. All carbon coaxial supercapacitors based on hollow carbon nanotube sleeve structure. Nanotechnology. 2015; 26 :1-8. DOI: 10.1088/0957-4484/26/4/045401 - 94.
Iyyamperumai E, Wang S, Dai L. Vertically aligned BCN nanotubes with high capacitance. ACS Nano. 2012; 6 :5259-5265. DOI: 10.1021/nn301044v - 95.
Xu Y, Zhyang SQ, Zhang XY, He PG, Fang YZ. Configuration and capacitance properties of polypyrrole/aligned carbon nanotubes synthesized by electropolymerization. Chinese Science Bulletin. 2011; 56 :3823-3828. DOI: 10.1007/s11434-011-4745-z - 96.
Hiralal P, Wang H, Unalan HE, Liu Y, Rouvala M, Wei D, Andrew P, Amaratunga AJ. Enhanced supercapacitors from hierarchical carbon nanotube and nanohorn architectures. Journal of Materials Chemistry. 2011; 21 :17810-17815. DOI: 10.1039/c1jm12156a - 97.
Tran M-H, Jeong HK. Ternary carbon composite films for supercapacitor applications. Chemical Physics Letters. 2017; 684 :1-7. DOI: 10.1016/j.cplett.2017.06.025 - 98.
Yu D, Goh K, Wang H, Wei L, Jiang W, Zhang Q, Dai L, Chen Y. Scalable synthesis of hierarchically structured carbon nanotube–graphene fibers for capacitive energy storage. Nature Nanotechnology. 2014; 9 :555-562. DOI: 10.1038/NNANO.2014.93 - 99.
Pham DT, Lee TH, Luong DH, Yao F, Ghosh A, Le VT, Kim TH, Li B, Chang J, Lee YH. Carbon nanotube-bridged graphene 3D building blocks for ultrafast compact supercapacitors. ACS Nano. 2015; 9 :2018-2027. DOI: 10.1021/nn507079x - 100.
Yu D, Dai L. Self-assembled graphene/carbon nanotube hybrid films for supercapacitors. The Journal of Physical Chemistry Letters. 2010; 1 :467-470. DOI: 10.1021/jz9003137 - 101.
Jha N, Ramesh P, Bekyarova E, Itkis ME, Haddon RC. High energy density supercapacitor based on a hybrid carbon nanotube-reduced graphite oxide architecture. Advanced Energy Materials. 2012; 2 :438-444. DOI: 10.1002/aenm.201100697 - 102.
Du F, Yu D, Dai L, Ganguli S, Varshney V, Roy AK. Preparation of tunable 3D pillared carbon nanotube-graphene networks for high-performance capacitance. Chemistry of Materials. 2011; 23 :4810-4816. DOI: 10.1021/cm2021214 - 103.
Huang Z-D, Zhang B, S-W O, Zheng Q-B, Lin X-Y, Yousefi N, Kim J-K. Self-assembled reduced graphene oxide/carbon nanotube thin films as electrodes for supercapacitors. Journal of Materials Chemistry. 2012; 22 :3591-3599. DOI: 10.1039/c2jm15048d - 104.
Byon HR, Gallant BM, Lee SW, Shao-Horn Y. Role of oxygen functional groups in carbon nanotube/graphene freestanding electrodes for high performance lithium batteries. Advanced Functional Materials. 2013; 23 :1037-1045. DOI: 10.1002/adfm.201200697 - 105.
Zheng Q, Cai Z, Ma Z, Gong S. Cellulose nanofibril/reduced graphene oxide/carbon nanotube hybrid aerogels for highly flexible and all-solid-state supercapacitors. ACS Applied Materials & Interfaces. 2015; 7 :3263-3271. DOI: 10.1021/am507999s - 106.
Wang Q, Yan J, Wang Y, Ning G, Fan Z, Wei T, Cheng J, Zhang M, Jing X. Template synthesis of hollow carbon spheres anchored on carbon nanotubes for high rate performance supercapacitors. Carbon. 2013; 52 :209-218. DOI: 10.1016/j.carbon.2012.09.022 - 107.
Lin J, Zhang C, Yan Z, Zhu Y, Peng Z, Hauge RH, Natelson D, Tour JM. 3-dimensional graphene carbon nanotube carpet-based microsupercapacitors with high electrochemical performance. Nano Letters. 2013; 13 :72-78. DOI: 10.1021/nl3034976 - 108.
Sivakkumar SR, Kim WJ, Choi J-A, MacFarlane DR, Forsyth M, Kim D-W. Electrochemical performance of polyaniline nanofibres and polyaniline/multi-walled carbon nanotube composite as an electrode material for aqueous redox supercapacitors. Journal of Power Sources. 2007; 171 :1062-1068. DOI: 10.1016/j.jpowsour.2007.05.103 - 109.
Ghosh A, Lee YH. Carbon-based electrochemical capacitors. Chemistry & Sustainability Energy & Materials. 2012; 5 :480-499. DOI: 10.1002/cssc.201100645 - 110.
Peng C, Jin J, Chen GZ. A comparative study on electrochemical co-deposition and capacitance of composite films of conducting polymers and carbon nanotubes. Electrochimica Acta. 2007; 53 :525-537. DOI: 10.1016/j.electacta.2007.07.004 - 111.
Gupta V, Miura N. Polyaniline/single-wall carbon nanotube (PANI/SWCNT) composites for high performance supercapacitors. Electrochimica Acta. 2006; 52 :1721-1726. DOI: 10.1016/j.electacta.2006.01.074 - 112.
Zhang J, Kong L-B, Wang B, Luo Y-C, Kang L. In-situ electrochemical polymerization of multi-walled carbon nanotube/polyaniline composite films for electrochemical supercapacitors. Synthetic Metals. 2009; 159 :260-266. DOI: 10.1016/j.synthmet.2008.09.018 - 113.
Canobre SC, Almeida DAL, Fonseca CP, Neves S. Synthesis and characterization of hybrid composites based on carbon nanotubes. Electrochimica Acta. 2009; 54 :5383-6388. DOI: 10.1016/j.electacta.2009.06.002 - 114.
Paul S, Lee Y-S, Choi J-A, Kang YC, Kim D-W. Synthesis and electrochemical characterization of polypyrrole/multi-walled carbon nanotube composite electrodes for supercapacitor applications. Bulletin of the Korean Chemical Society. 2010; 31 :1228-1323. DOI: 10.5012/bkcs.2010.31.5.1228 - 115.
Branzoi V, Branzoi F, Pilan L. Electrochemical fabrication and capacitance of composite films of carbon nanotubes and polyaniline. Surface & Interface Analysis. 2009; 42 :1266-1270. DOI: 10.1002/sia.3387 - 116.
Chen X, Paul R, Dai L. Carbon-based supercapacitors for efficient energy storage. National Science Review. 2017; 4 :1-37. DOI: 10.1093/nsr/nwx009 - 117.
Teresawa N, Asaka K. High-performance PEDOT:PSS/single-walled carbon nanotube/ionic liquid actuators combining electrostatic double-layer and faradaic capacitors. Langmuir. 2016; 32 :7210-7218. DOI: 10.1021/acs.langmuir.6b01148 - 118.
Peng C, Zhang S, Jewell D, Chen GZ. Carbon nanotube and conducting polymer composites for supercapacitors. Progress in Natural Science. 2008; 18 :777-788. DOI: 10.1016/j.pnsc.2008.03.002 - 119.
Grądzka E, Winkler K, Borowska M, Plonska-Brzezinka ME, Echegoyen L. Comparison of the electrochemical properties of thin films of MWCNTs/C60-Pd, SWCNTs/C60-Pd and ox-CNOs/C60-Pd. Electrochimica Acta. 2013; 96 :274-284. DOI: 10.1016/j.electacta.2013.02.035 - 120.
Lee KYT, Shi HTH, Lian K, Naguib HE. Flexible multiwalled carbon nanotubes/conductive polymer composite electrode for supercapacitor applications. Smart Materials and Structures. 2015; 24 :1-17. DOI: 10.1088/0964-1726/24/11/115008 - 121.
Kausar A. Performance of polyaniline doped carbon nanotube composite. American Journal of Polymer Science and Engineering. 2017; 5 :43-54 - 122.
Raicopol M, Pruna A, Pilan L. Supercapacitance of single-walled carbon nanotubes-polypyrrole composites. Journal of Chemistry. 2013:1-7. DOI: 10.1155/2013/367473 - 123.
Maubane M, Mamo MA, Nxumalo EN, van Otterlo WAL, Coville NJ. Tubular shaped composites made from polythiophene covalently linked to Prato functionalized N-doped carbon nanotubes. Synthetic Metals. 2012; 162 :2307-2315. DOI: 10.1016/j.synthmet.2012.10.020 - 124.
Wei D, Kvarnstrom C, Lindfors T, Ivaska A. Electrochemical functionalization of single walled carbon nanotubes with polyaniline in ionic liquids. Electrochemistry Communications. 2007; 9 :206-210. DOI: 10.1016/j.elecom.2006.09.008 - 125.
Angeles Herranz M, Martin N. Noncovalent functionalization of carbon nanotubes. In: Guldi DM, Martin N, editors. Carbon Nanotubes and Related Structures. Synthesis, Characterization, Functionalization, and Application. Weinheim: Wiley-VCH Verlag GmbH & Co. KgaA 2010. P. 103-134. DOI: 10.1002/9783527629930.ch5 - 126.
Liu L, Yoo S-H, Park S. Composite materials with MWCNTs and conducting polymer nanorods and their application as supercapacitors. Journal of Electrochemical Science and Technology. 2010; 1 :25-30. DOI: 10.5229/JECST.2010.1.1.025 - 127.
Frackowiak E, Khomenko V, Jurewicz K, Lota K, Beguin F. Supercapacitors based on conducting polymers/nanotubes composites. Journal of Power Sources. 2006; 153 :413-418. DOI: 10.1016/j.jpowsour.2005.05.030 - 128.
Cheng Q, Tang J, Shinya N, Qin L-C. Polyaniline modified graphene and carbon nanotube composite electrode for asymmetric supercapacitors of high energy density. Journal of Power Sources. 2013; 241 :423-428. DOI: 10.1016/j.jpowsour.2013.04.105 - 129.
Plonska-Brzezinska ME, Breczko J, Palys B, Echegoyen L. The electrochemical properties of nanocomposite films obtained by chemical in situ polymerization of aniline and carbon nanostructures. A European Journal of Chemical Physics and Phyical Chemistry. 2013; 14 :116-124. DOI: 10.1002/cphc.201200759 - 130.
Khomenko V, Frackowiak E, Beguin F. Determination of the specific capacitance of conducting polymer/nanotubes composite electrodes using different cell configurations. Electrochimica Acta. 2005; 50 :2499-2506. DOI: 10.1016/j.electacta.2004.10.078 - 131.
Aphale A, Maisuria K, Mahapatra MK, Santiago A, Singh P, Patra P. Hybrid electrodes by in-situ integration of graphene and carbon-nanotubes in polypyrrole for supercapacitors. Scientific Reports. 2015; 5 (14445):1-8. DOI: 10.1038/srep14445 - 132.
Zhou C, Kumar S, Doyle CD, Tour JM. Functionalized single wall carbon nanotubes treated with pyrrole for electrochemical supercapacitor membranes. Chemistry of Materials. 2005; 17 :1997-2002. DOI: 10.1021/cm047882b - 133.
Liu J, Sun J, Gao L. A promising way to enhance the electrochemical behavior of flexible single-walled carbon nanotube/polyaniline composite films. Journal of Physical Chemistry C. 2010; 114 :19614-19620. DOI: 10.1021/jp1092042 - 134.
Mikhaylova AA, Tusseeva EK, Mayrova NA, Rychagov AY, Volfkovich YM, Krestinin AV, Khazova O. Single-walled carbon nanotubes and their composites with polyaniline. Structure, catalytic and capacitive properties as applied to fuel cells and supercapacitors. Electrochimica Acta. 2011; 56 :3656-3665. DOI: 10.1016/j.electacta.2010.07.021 - 135.
Yang P, Chen Y, Yu X, Qiang P, Wang K, Cai X, Tan S, Liu P, Song J, Mai W. Reciprocal alternate deposition strategy using metal oxide/carbon nanotube for positive and negative electrodes of high-performance supercapacitors. Nano Energy. 2014; 10 :108-116. DOI: 10.1016/j.nanoen.2014.08.018 - 136.
Wu M-S. Electrochemical capacitance from manganese oxide nanowire structure synthesized by cyclic voltammetric electrodeposition. Applied Physics Letters. 2005; 87 :153102-1-153102-3. DOI: 10.1063/1.2089169 - 137.
Devaraj S, Munichandraiah N. Effect of crystallographic structure of MnO2 on its electrochemical capacitance properties. Journal of Physical Chemistry C. 2008; 112 :4406-4417. DOI: 10.1021/jp7108785 - 138.
Jiang H, Zhao T, Ma J, Yan C, Li C. Ultrafine manganese dioxide nanowire network for high-performance supercapacitors. Chemical Communications. 2011; 47 :1264-1266. DOI: 10.1039/c0cc04134c - 139.
Yan J, Khoo E, Sumboja A, Lee PS. Facile coating of manganese oxide on tin oxide nanowires with high-performance capacitive behavior. ACS Nano. 2010; 4 :4247-4255. DOI: 10.1021/nn100592d - 140.
Jiang R, Huang T, Liu J, Zhuang J, Yu A. A novel method to prepare nanostructured manganese dioxide and its electrochemical properties as a supercapacitor electrode. Electrochimica Acta. 2009; 54 :3047-3052. DOI: 10.1016/j.electacta.2008.12.007 - 141.
Beadrouet E, Le Gal La Salle A, Guyomard D. Nanostructured manganese dioxides: Synthesis and properties as supercapacitor electrode materials. Electrochimica Acta. 2009; 54 :1240-1248. DOI: 10.1016/j.electacta.2008.08.072 - 142.
Wei W, Cui X, Chen W, Ivey DG. Electrochemical cyclability mechanism for MnO2 electrodes utilized as electrochemical supercapacitors. Journal of Power Sources. 2009; 186 :843-550. DOI: 10.1016/j.jpowsour.2008.10.058 - 143.
Xia H, Wang Y, Lin J, Lu L. Hydrothermal synthesis of MnO2/CNT nanocomposite with a CNT core/porous MnO2 sheath hierarchy architecture for supercapacitors. Nanoscale Research Letters. 2012; 7 (33):1-10. DOI: 10.1186/1556-276X-7-33 - 144.
Kang J, Hirata A, Kang L, Zhang X, Hou Y, Chen L, Li C, Fujita T, Akagai K, Chen M. Enhanced supercapacitor performance of MnO2 by atomic doping. Angewandte Chemie. 2013; 125 :1708-1711. DOI: 10.1002/ange.201208993 - 145.
Yan J, Fan Z, Wei T, Cheng J, Shao B, Wang K, Song L, Zhang M. Carbon nanotube/MnO2 composites synthesized by microwave-assisted method for supercapacitors with high power and energy densities. Journal of Power Sources. 2009; 194 :1202-1207. DOI: 10.1016/j.jpowsour.2009.06.006 - 146.
Ma S-B, Nam K-W, Yoon W-S, Yang X-Q, Ahn K-Y, Oh K-H, Kim K-B. A novel concept of hybrid capacitor based on manganese oxide materials. Electrochemistry Communications. 2007; 9 :2807-2811. DOI: 10.1016/j.elecom.2007.09.015 - 147.
Xie X, Gao L. Characterization of a manganese dioxide/carbon nanotube composite fabricated using an in situ coating method. Carbon. 2007; 45 :2365-2373. DOI: 10.1016/j.carbon.2007.07.014 - 148.
Jin X, Zhou W, Zhang S, Chen GZ. Nanoscale microelectrochemical cells on carbon nanotubes. Small. 2007; 3 :1513-1517. DOI: 10.1002/smll.200700139 - 149.
Chen P-C, Shen G, Shi Y, Zhou C. Preparation and characterization of flexible asymmetric supercapacitors based on transition-metal-oxide nanowire/single-walled carbon nanotube hybrid thin-film electrodes. ACS Nano. 2010; 4 :4403-4411. DOI: 10.1021/nn100856y - 150.
Zhang H, Gao G, Wang Z, Yang Y, Shi Z, Gu Z. Growth of manganese oxide nanoflowers on vertically-aligned carbon nanotube arrays for high-rate electrochemical capacitive energy storage. Nano Letters. 2008; 8 :2664-2668. DOI: 10.1021/nl800925j - 151.
Bi R-R, X-L W, Cao F-F, Jiang L-Y, Guo Y-G, Wan L-J. Highly dispersed RuO2 nanoparticles on carbon nanotubes: Facile synthesis and enhanced supercapacitance performance. Journal of Physical Chemistry C. 2010; 114 :2448-2451. DOI: 10.1021/jp9116563 - 152.
Chen P, Chen H, Qiu J, Zhou C. Inkjet printing of single-walled carbon nanotube/RuO2 nanowire supercapacitors on cloth fabrics and flexible substrates. Nano Research. 2010; 3 :594-603. DOI: 10.1007/s12274-010-0020-x - 153.
Reddy ALM, Ramaprabhu S. Nanocrystalline metal oxides dispersed multiwalled carbon nanotubes as supercapacitor electrodes. Journal of Physical Chemistry C. 2007; 111 :7727-7734. DOI: 10.1021/jp069006m - 154.
Yan S, Wang HW, Qu P, Zhang Y, Xiao Z. RuO2/carbon nanotubes composites synthesized by microwave-assisted method for electrochemical supercapacitor. Synthetic Metals. 2009; 159 :158-161. DOI: 10.1016/j.synthmet.2008.07.024 - 155.
Lee JY, Liang K, An KH, Lee YH. Nickel oxide/carbon nanotubes nanocomposite for electrochemical capacitance. Synthetic Metals. 2005; 150 :153-157. DOI: 10.1016/j.synthmet.2005.01.016 - 156.
Gao B, Yuan B-Z, L-H S, Chen L, Zhang X-G. Nickel oxide coated on ultrasonically pretreated carbon nanotubes for supercapacitor. Journal of Solid State Electrochemistry. 2009; 13 :1251-1257. DOI: 10.1007/s10008-008-0658-4 - 157.
Zhao X, Johnston C, Grant PS. A novel hybrid supercapacitor with a carbon nanotube cathode and an iron oxide/carbon nanotube composite anode. Journal of Materials Chemistry. 2009; 19 :8755-8760. DOI: 10.1039/b909779a - 158.
Shan Y, Gao L. Formation and characterization of multi-walled carbon nanotubes/Co3O4 nanocomposites for supercapacitors. Materials Chemistry and Physics. 2007; 103 :206-210. DOI: 10.1016/j.matchemphys.2007.02.038 - 159.
Aravinda LS, Nagaraja KK, Udaya Bhat K, Bhat BR. Magnetron sputtered MoO3/carbon nanotube composite electrodes for electrochemical supercapacitor. Journal of Electroanalytical Chemistry. 2013; 699 :28-32. DOI: 10.1016/j.jelechem.2013.03.022 - 160.
Sathiya M, Prakash AS, Ramesha K, Tarascon J-M, Shukla AK. V2O5-anchored carbon nanotubes for enhanced electrochemical energy storage. Journal of the American Chemical Society. 2011; 133 :16291-16299. DOI: 10.1021/ja207285b - 161.
Enterria M, Goncalves AG, Pereira MFR, Martins JI, Figueiredo JL. Electrochemical storage mechanisms in non-stoichiometric cerium oxide/multiwalled carbon nanotube composites. Electrochimica Acta. 2016; 209 :25-35. DOI: 10.1016/j.electacta.2016.05.036 - 162.
Wang X, Han X, Lim M, Singh N, Gan NS, Jan M, Lee PS. Nickel cobalt oxide-single wall carbon nanotube composite material for superior cycling stability and high-performance supercapacitor application. Journal of Physical Chemistry C. 2012; 116 :12448-12454. DOI: 10.1021/jp3028353 - 163.
Chiang DNK, Lim SS, Peng C. Novel bimetallic tin-manganese oxides/carbon nanotube nanocomposite and their charge storage properties. Journal—the Institution of Engineers, Malysia. 2014; 75 (1):24-39 - 164.
Jang JH, Kato A, Machida K, Naoi K. Supercapacitor performance of hydrous ruthenium oxide electrodes prepared by electrophoretic deposition. Journal of the Electrochemical Society. 2006; 153 :A321-A328. DOI: 10.1149/1.2138672 - 165.
Tao T, Zhang L, Jiang H, Li C. Functional carbon nanotube/mesoporous carbon/MnO2 hybrid network for high-performance supercapacitors. Journal of Nanomaterials. 2014; 2014 :1-6. DOI: 10.1155/2014/568561 - 166.
Bordjiba T, Mohamedi M. Molding versus dispersion: Effect of the preparation procedure on the capacitive and cycle life of carbon nanotubes aerogel composites. Journal of Solid State Electrochemistery. 2011; 15 :765-771. DOI: 10.1007/s10008-010-1155-0 - 167.
Kim SJ, Hwang SW, Hyun SH. Preparation of carbon aerogel electrodes for supercapacitor and their electrochemical characteristics. Journal of Materials Science. 2005; 40 :725-731. DOI: 10.1007/s10853-005-6313-x - 168.
Kim C-Y, Jang AR, Cho Y. Optimization of pore structures and supercapacitor properties of carbon aerogel electrodes. Asian Journal of Chemistry. 2012; 24 :4205-4212 - 169.
Macias C, Rasines G, Garcia TE, Zafra MC, Lavela P, Tirado JL, Ania CO. Synthesis of porous and mechanically compliant carbon aerogels using conductive and structural additives. Gels. 2016; 2 :1-16. DOI: 10.3390/gels2010004 - 170.
Bordjiba T, Mohamedi M, Dao LH. Novel binderless nanostructured carbon nanotubes—carbon aerogel composites for electrochemical double layer capacitors. ECS Transactions. 2008; 6 :183-189. DOI: 10.1149/1.2943237 - 171.
Bordjiba T, Mohamedi M, Dao LH. Charge storage mechanism of binderless nanocomposite electrodes formed by dispersion of CNTs and carbon aerogels. Journal of the Electrochemical Society. 2008; 155 :A115-A124 - 172.
Bordjiba T, Mohamedi M, Dao LH. Synthesis and electrochemical capacitance of binderless nanocomposite electrodes formed by dispersion of carbon nanotubes and carbon aerogels. Journal of Power Sources. 2007; 172 :991-998. DOI: 10.1016/j.jpowsour.2007.05.011 - 173.
Hao P, Zhao Z, Li L, Tuan C-C, Li H, Sang Y, Jiang H, Wong PC, Liu H. The hybrid nanostructure of MnCo2O4.5 nanoneedle/carbon aerogel for symmetric supercapacitors with high energy density. Nanoscale. 2015; 7 :14401-14412. DOI: 10.1039/c5nr04421a - 174.
Annamalai KP, Fathy NA, Tao Y. Synthesis and capacitance performance of phosphorous-enriched carbon xerogel. Journal of Sol-Gel Science and Technology. DOI: 10.1007/s10971-017-4452-6 - 175.
Lufrano F, Staiti P, Calvo EG, Juarez-Perez EJ, Menendez JA, Arenillas A. Carbon xerogel and manganese oxide capacitive materials for advanced supercapacitors. International Journal of Electrochemical Science. 2011; 6 :596-612 - 176.
Liu X, Li S, Mi R, Liu L-M, Cao H, Lau W-M, Liu H. Porous structure design of carbon xerogels for advanced supercapacitor. Applied Energy. 2015; 153 :32-40. DOI: 10.1016/j.apenergy.2015.01.141 - 177.
Ordenanan-Martinez AS, Rincon ME, Vargas M, Estrada-Vargas A, Casillas N, Barcena-Sato M, Ramos E. Carbon nanotubes/carbon xerogel-nafion electrodes: A comparative study of preparation methods. Journal of Solid State Electrochemistry. 2012; 16 :3777-3782. DOI: 10.1007/s10008-012-1819-z - 178.
Fernandez PS, Castro EB, Real SG, Visintin A, Arenillas A, Calvo EG, Juarez-Perez EJ, Menendez AJ, Martins ME. Electrochemical behavior and capacitance properties of carbon xerogel/multiwalled carbon nanotubes composites. Journal of Solid State Electrochemistry. 2012; 16 :1067-1076. DOI: 10.1007/s10008-011-1487-4