Fabrication and electrochemical properties of carbon nanotube array electrode for supercapacitors

The multiwalled carbon nanotube (MWNT) array was fabricated by chemical vapor deposition (CVD) in the template of porous alumina from the carbonaceous source of C₂H₂ in the presence of a catalyst of ferric metals. To utilize the external surface other than the inner surface of the carbon nanotubes, 1 mol/L sulfuric acid was applied to remove off the most part of AAO template on the carbon nanotube electrode. The electrochemical performances of the carbon nanotube array electrode were investigated by use of the cyclic voltammetry, galvanostatic charge/discharge and ac impedance methods for its application in supercapacitors. The specific capacitance of 365 F/g of the electrode was achieved with the discharge current density of 210 mA/g in the solution of 1 mol/L H₂SO₄. In addition, the carbon nanotube array electrode was found to have low equivalent series resistance (ESR) and good cycling stability.     

Transparent and flexible electrodes and supercapacitors using polyaniline/single-walled carbon nanotube composite thin films

Large-scale transparent and flexible electronic devices have been pursued for potential applications such as those in touch sensors and display technologies. These applications require that the power source of these devices must also comply with transparent and flexible features. Here we present transparent and flexible supercapacitors assembled from polyaniline (PANI)/single-walled carbon nanotube (SWNT) composite thin film electrodes. The ultrathin, optically homogeneous and transparent, electrically conducting films of the PANI/SWNT composite show a large specific capacitance due to combined double-layer capacitance and pseudo-capacitance mechanisms. A supercapacitor assembled using electrodes with a SWNT density of 10.0 μg cm(-2) and 59 wt% PANI gives a specific capacitance of 55.0 F g(-1) at a current density of 2.6 A g(-1), showing its possibility for transparent and flexible energy storage.     

Fabrication of carbon nanotube thin films on flexible substrates by spray deposition and transfer printing

We present two different processes for the deposition of high quality CNT films on flexible substrates. The first is a simple and low cost transfer printing process that transfers CNT films deposited on glass to a flexible substrate in few steps. The second is the utilization of a low cost spray process for the direct deposition of CNT films on flexible substrates. Both processes are reliable, reproducible and result in highly uniform CNT films which are comparable to the state-of-the-art CNT films fabricated on glass substrates. CNT films with 19 nm thickness and with an optical transmission up to 86% at a sheet resistance of 250 Ω/sq have been fabricated on flexible substrates.     

Fabrication of carbon nanotube emitter on the flexible substrate

Carbon nanotube (CNT) emitter on the flexible substrate was developed by simple printing of CNT composite containing spin on glass (SOG) on indium tin oxide (ITO) coated polyethylene terephthalate (PET) film and heat treatment at 150 °C. Mixture of terpineol and binder polymer such as ethyl cellulose and acryl was used as an organic vehicle in CNT composite. Si and O atoms from SOG were uniformly dispersed and formed silica bonding in CNT composite after heat treatment at 150 °C. Adhesion between CNT composite and the PET substrate was excellent. Turn-on electric field of CNT emitter was 2.9 V/μm. Sheet resistance of CNT composite was about 30 Ohm/sq.     

Cooperative effect of hierarchical carbon nanotube arrays as facilitated transport channels for high-performance wire-based supercapacitors

It is demonstrated that hierarchical nanostructures can greatly enhance the performances of a wire-based supercapacitor (WS), meanwhile can also increase the WS's volume and further hamper the improvement of the WS's capacitance per unit volume. Here a type of three dimensional hierarchical MnO₂@carbon nanotube array (CNTA) composites has been designed on stainless steel wires (SSWs) and the cooperative effects of various parameters (such as MnO₂ masses, CNTA lengths and wire lengths) on the electrochemical performances of the wire electrodes are systematically investigated. Results show that the specific capacitance of the electrodes can be optimized by MnO₂ masses and array lengths, while independent to wire lengths. Moreover, the optimized MnO₂@CNTA/SSW electrodes can exhibit high capacitance (9.1 mF cm⁻¹ at 5 mV s⁻¹), good rate-capability (64.46% at 3 A cm⁻³), and high cycle retention (84.8% after 1000 cycles). Furthermore, the assembled all-solid state flat symmetrical WSs show desirable capacitive behaviors (∼0.78 mW h cm⁻³) and good flexibility.     

A flexible graphene/multiwalled carbon nanotube film as a high performance electrode material for supercapacitors

A flexible graphene/multiwalled carbon nanotube (GN/MWCNT) film has been fabricated by flow-directed assembly from a complex dispersion of graphite oxide (GO) and pristine MWCNTs followed by the use of gas-based hydrazine to reduce the GO into GN sheets. The GN/MWCNT (16 wt.% MWCNTs) film characterized by Fourier transformation infrared spectra, X-ray diffraction and scanning electron microscope has a layered structure with MWCNTs uniformly sandwiched between the GN sheets. The MWCNTs in the obtained composite film not only efficiently increase the basal spacing but also bridge the defects for electron transfer between GN sheets, increasing electrolyte/electrode contact area and facilitating transportation of electrolyte ion and electron into the inner region of electrode. Electrochemical data demonstrate that the GN/MWCNT film possesses a specific capacitance of 265 F g⁻¹ at 0.1 A g⁻¹ and a good rate capability (49% capacity retention at 50 A g⁻¹), and displays an excellent specific capacitance retention of 97% after 2000 continuous charge/discharge cycles. The results of electrochemical measurements indicate that the freestanding GN/MWCNT film has a potential application in flexible energy storage devices.     

Spectroscopic study of double-walled carbon nanotube functionalization for preparation of carbon nanotube / epoxy composites

A spectroscopic study of the amino functionalization of double-walled carbon nanotubes (DWCNT) is performed. Original experimental investigations by near edge X-ray absorption fine structure spectroscopy at the C and O K-edges allow one to follow the efficiency of the chemistry during the different steps of covalent functionalization. Combined with Raman spectroscopy, the characterization gives direct evidence of the grafting of amino-terminated molecules on the structural defects of the DWCNT external wall, whereas the internal wall does not undergo any change. Structural and mechanical investigations of the amino functionalized DWCNT/epoxy composites show coupling between epoxy molecules and the DWCNTs. Functionalization improves the interface between amino-functionalized DWCNT and the epoxy molecules. Electrical transport measurements indicate a percolating network formed only by the inner metallic tubes of the DWCNTs. The activation energy of the barrier between connected metallic tubes is determined to be around 20 meV.     

碳纳米管的非共价功能化研究进展

综述了碳纳米管非共价功能化的一些新的研究进展情况,介绍了碳纳米管非共价功化的种类、方法和意义,并对功能化后的碳纳米管的性能表征方法及应用前景进行了介绍。针对碳纳米管非共价功能化后虽可同时保持原有的物化性质和引入的物化性质,但表征非常困难这一矛盾进行了评述,并对今后的发展进行了展望。     

Fabrication of patterned carbon nanotube thin films using electrophoretic deposition and ultrasonic radiation

A simple wet-deposition method for preparing patterned carbon nanotube (CNT) thin films is reported. Using electrophoretic deposition (EPD), CNTs were deposited over indium tin oxide (ITO) plates that had been patterned with a photoresist; consequently, CNTs covered not only the exposed ITO areas but also the photoresist areas because thinness of the photoresists could not prevent the transverse deposition of CNTs over the photoresist areas. The ultrasonic treatment for the samples removed only CNTs on the photoresist areas, resulting in the formation of patterned CNT thin films, because Ni metal formed during EPD connects CNTs to ITO plates.     

Carbon nanotube cloth as a promising electrode material for flexible aqueous supercapacitors

Journal of Applied Electrochemistry - Electrochemical cyclic recharging of a binder-free flexible carbon material in respect to supercapacitor applications is reported. To provide high enough and...     

Contamination-free and damage-free patterning of single-walled carbon nanotube transparent conductive films on flexible substrates

High quality patterning of single-walled carbon nanotube (SWCNT) transparent conductive films is achieved by a lift-off aluminum interlayer method, which has the advantage of resulting in contamination-free and damage-free SWCNTs. The obtained patterns preserve the electrical properties of the SWCNT films and show promising applications in flexible high frequency electronic and display devices.     

Hydrothermal synthesis and activation of graphene-incorporated nitrogen-rich carbon composite for high-performance supercapacitors

Graphene-incorporated nitrogen-rich carbon composite with nitrogen content of ca. 10 wt.% has been synthesized by an effective yet simple hydrothermal reaction of glucosamine in the presence of graphene oxide (GO). The nitrogen content of carbon composite is nearly twice as high as that of hydrothermal carbon without graphene. GO is favorable for the high nitrogen doping in the carbon composite by the reaction between the glucosamine-released ammonia and GO. The hydrothermal carbon composite is further activated by KOH, and graphene in the activated carbon composite demonstrates a positive effect of increasing specific surface area, pore volume and electrical conductivity, resulting in superior electrochemical performance. The activated carbon composite with higher specific surface area and micropore volume possesses higher specific capacitance with a value of 300 F g⁻¹ at 0.1 A g⁻¹ in 6 M KOH aqueous solution in the two electrode cell. Larger mesopore volume and higher conductivity of the activated carbon composite will provide fast ion and electron transfer, thus leading to higher rate capacity with a capacitance retention of 76% at 8 A g⁻¹ in comparison to the activated hydrothermal carbon without graphene.     

Decoration of carbon cloth by manganese oxides for flexible asymmetric supercapacitors

Here we describe the production of carbon cloth coated with MnO₂ nanosheets or MnOOH nanorods through a normal temperature reaction or a hydrothermal approach, respectively. Of note, the electrochemical performance of MnO₂-coated carbon cloth was better (429.2 F g⁻¹) than that of MnOOH-coated carbon cloth. When the MnO₂-coated carbon cloth is introduced as the positive electrode and the Fe₂O₃-coated carbon cloth as the negative electrode, a flexible asymmetric supercapacitor was obtained with an energy density of 22.8 Wh kg⁻¹ and a power density of 159.4 W kg⁻¹. Therefore, such a hierarchical MnO₂-coated carbon cloth nanocomposite is a promising high-performance electrode for flexible supercapacitors.     

Lamellar flower inspired hierarchical alpha manganese vanadate microflowers for high-performance flexible hybrid supercapacitors

Hybrid flexible supercapacitors (HFS) offer high power density and stability making them an ideal choice for the energy storage system in wearable devices. In this work, the synthesis of lamellar flower-like alpha manganese vanadate (α-Mn₂V₂O₇) on nickel foam was proposed for efficient and highly stable HFS applications for the first time. The voltammetric characterization indicated that the capacitance contribution of α-Mn₂V₂O₇ is derived from the diffusion-controlled (battery-type, 89.93%) and capacitive controlled (10.07%) mechanisms in aqueous electrolyte (0.5 M KOH). The optimized α-Mn₂V₂O₇ electrode exhibited an impressive specific capacity of 125.6 mAhg^?1 (760.3 Fg^-1). In the HFS device configuration, the utilization of α-Mn₂V₂O₇ resulted in a remarkable specific capacitance of 35.7 F g^?1 with energy, and a power density of 28.4 Whkg^?1 and 8.5 kWkg^?1, respectively. Furthermore, the α-Mn₂V₂O₇ fabricated device is found to operate in a wide potential window exhibiting remarkable and stable electrochemical performance in the gel electrolyte even under mechanical stress conditions. Importantly, the α-Mn₂V₂O₇ HFS showed an impressive and stable performance over 5000 cycles. The superior specific capacitance performances obtained in the present study are noted to be the best results reported for vanadium-based ternary oxides so far.     

Material advancements in supercapacitors: From activated carbon to carbon nanotube and graphene

The electrochemical capacitor (EC), also known as supercapacitor, is an energy storage device possessing a near infinite life‐cycle and high power density recognised to store energy in the double‐layer or through pseudocapacitance as a result of an applied potential. Fundamental principles of charge storage in relation to the important physical and chemical characteristics of electrode materials are addressed in the following review, with carbon‐made electrodes, specifically activated carbon, carbon fibres and aerogels, carbon nanotubes and graphene emphasised in regards to their enhancement of the characteristic energy and power densities of ECs. Pseudocapacitive materials, notably transition metal oxides and nitrides, and conducting polymers are remarked by the potential to further improve EC performance through synergistic effects and asymmetric design. Research towards gaining a better understanding of charge storage in sub‐micropores, material design and improving the performance of alternative electrolytes are expected to greatly enhance the capabilities of these devices in the near future.     

Barnacle-like manganese oxide decorated porous carbon nanofibers for high-performance asymmetric supercapacitors

In this study, barnacle-like manganese oxide (MnO₂) decorated porous carbon nanofibers (PCNF) were synthesized using electrospinning and the chemical precipitation method for high-performance asymmetric supercapacitors. The porous structure of PCNF was acquired using poly(styrene-co-acrylonitrile) in the electrospinning solution. In order to obtain the optimized barnacle-like MnO₂ on PCNF (MnO₂-PCNF), the barnacle-like MnO₂ was synthesized using different synthetic times (namely, 1.5, 3.0, and 7.0 min) of the chemical precipitation. Among them, the optimized MnO₂-PCNF for 3.0 min exhibited the well-dispersed MnO₂ on the PCNF with the nano-size of 190–218 nm. The optimized MnO₂-PCNF showed the superior specific capacitance of 209.8 F g^?1 at 10 mV s^?1 and the excellent high-rate performance of 160.3 F g^?1 at 200 mV s^?1 with the capacitance retention of 98.7% at 100 mV s^?1 for 300 cycles. In addition, electrochemical performances of asymmetric cell (constructed activated carbon and MnO₂-PCNF) showed the high specific capacitance of 60.6 F g^?1 at the current density of 0.5 A g^?1, high-rate capacitance of 30.0 F g^?1 at the current density of 10 A g^?1, and the excellent energy density of 30.3–15.0 Wh kg^?1 in the power density range from 270 to 9000 W kg^?1. The enhanced electrochemical performance can be explained by the synergistic effects of barnacle-like MnO₂ nanoparticles with a high active area related to high specific capacitance and well-dispersed MnO₂ with a short ion diffusion length related to the excellent high-rate performance.     

Growth of yolk-shell CuCo2S4 on NiO nanosheets for high-performance flexible supercapacitors

A poor electrical conductivity and short cycle life limits the wide application of transition metal oxides in energy storage applications. In this study, yolk-shell structured CuCo₂S₄ was grown on NiO nanosheets (NiO@CuCo₂S₄) via a hydrothermal method and vulcanization, which combined the synergistic interactions between Ni, Co, and Cu. The effect of varying the amount of the vulcanizing agent (thiourea) on the electrochemical performance of NiO@CuCo₂S₄ was also investigated. Moreover, the amount of thiourea not only tuned the morphology of the composite, but significantly influenced its electrochemical performance. When the Cu²⁺: Co²⁺: thiourea molar ratio in the precursor solution was 1:2:6, the obtained NiO@CuCo₂S₄ exhibited the best electrochemical performance of the various systems examined, with a specific capacitance of 1658 F g^?1 being achieved at 1 A g^?1. Density functional theory calculations further confirmed the excellent synergistic effect between NiO and CuCo₂S₄. In addition, the asymmetric supercapacitor composed of a NiO@CuCo₂S₄ positive electrode reached an ultrahigh energy density of 73 Wh kg^?1 at a power density of 802 W kg^?1, as well as excellent cycling stability (i.e., 91% capacitance retention after 5000 cycles). These results suggest that NiO@CuCo₂S₄ is a promising candidate for use in energy storage applications.