Carbon nanotube/graphene composite for enhanced capacitive deionization performance

In this study, single-walled carbon nanotubes were combined with graphene oxide nanosheets in aqueous dispersion and then chemically reduced to form the carbon nanotube/graphene (CNT/G) composite as electrodes for capacitive deionization (CDI). The structure of the CNT/G composite was highly porous, with single-walled carbon nanotubes (SWCNTs) sandwiched between graphene sheets that functioned as spacers and provided diffusion paths for smooth and rapid ion conduction. The associated increase in the electrical double-layer capacitance enhanced capacitive deionization performance. The CNT/G composite achieved a specific capacitance of 220 F/g and an electrosorption capacity of 26.42 mg/g with 100% regeneration, showing great potential as a high performance electrode material in CDI applications.     

One-step microwave synthesis of palladium–carbon nanotube hybrids with improved catalytic performance

A fast and easy one-step linker-free approach for the synthesis of palladium nanoparticle/multiwall carbon nanotube (Pd-NP/MWCNT) hybrid materials is described using microwave irradiation for the effective decomposition of Pd₂dba₃ complex in the presence of MWCNTs. High loadings of Pd nanoparticles (up to 40 wt.%) having sizes between 3 and 5 nm are deposited on the surface of MWCNTs within a time of only 2 min. The Pd-NP/MWCNT materials serve as efficient catalysts in C–C coupling as well as in hydrogenation reactions, all characterized by high conversion rates using a small amount of catalysts, high turnover frequency values and good recyclability.     

Controllable bulk growth of few-layer graphene/single-walled carbon nanotube hybrids containing Fe@C nanoparticles in a fluidized bed reactor

A family of layered double hydroxides (LDHs) with varied Fe contents were employed as catalyst precursors for the controllable bulk growth of few-layer graphene/single-walled carbon nanotube (G/SWCNT) hybrids in a fluidized-bed reactor through chemical vapor deposition of methane at 950 °C. All the G/SWCNT hybrids exhibited the morphology of SWCNTs interlinked with graphene layers. The purity, thermal stability, graphitization degree, specific surface area, and total pore volume of the G/SWCNT hybrids decreased with the increasing Fe contents in the LDH precursors. A high yield of 0.97 g_G/SWCNTs/g_cat can be achieved by tuning the Fe content in the FeMgAl LDHs after a 15-min growth. After the removal of the as-calcined FeMgAl layered double oxide flakes, a high carbon purity of ca. 98.3% for G/SWCNT hybrids was achieved when the mole ratio of Fe–Al is 0.05:1. The size and density of Fe nanoparticles decorated in the as-obtained G/SWCNT hybrids depend largely on Fe content in the FeMgAl LDH precursors. Furthermore, the mass ratio of graphene materials to SWCNTs in the as-prepared G/SWCNT hybrids can be well controlled in a range of 0.4–15.1.     

PANI/煤基石墨烯宏观体复合材料的制备及其电化学性能

以太西无烟煤为原料,采用催化热处理、改良Hummers氧化等方法,制备煤基氧化石墨烯（CGO）,进而以CGO和聚苯胺（PANI）为前驱体,采用水热自组装法,制备得到PANI/石墨烯宏观体复合材料（3D-PCG）。采用FT-IR、XRD、Raman、SEM和TEM等技术,研究了材料的组成、结构和形貌,考察了3D-PCG的电化学性能。结果表明,PANI以纳米棒状形态均匀镶嵌在煤基石墨烯宏观体（3D-CG）的网状结构中;当PANI与CGO质量比为1：2时,3D-PCG的电化学性能优于PANI和3D-CG,其比电容可达663 F·g^-1。     

A multi-walled carbon nanotube/polymer actuator that surpasses the performance of a single-walled carbon nanotube/polymer actuator

Actuators were developed using activated and non-activated multi-walled carbon nanotube (MWCNT)–ionic liquid (IL) gel electrodes and compared to a single-walled carbon nanotube (SWCNT)-based actuator with respect to the electrochemical and electromechanical properties. The activated MWCNT–COOH/polymer actuator surpassed the SWCNT/polymer actuator in terms of the generated strain.     

Microwave autoclave synthesized multi-layer graphene/single-walled carbon nanotube composites for free-standing lithium-ion battery anodes

Multi-layer graphene sheets have been synthesized by a time-efficient microwave autoclave method and used to form composites in situ with single-walled carbon nanotubes. The application of these composites as flexible free-standing film electrodes was then investigated. According to the transmission electron microscopy and X-ray diffraction characterizations, the average d-spacing of the graphene–single-walled carbon nanotube composites was 0.41 nm, which was obviously larger than that of the as-prepared pure graphene (0.36 nm). The reversible Li-cycling properties of the free-standing films have been evaluated by galvanostatic discharge–charge cycling and electrochemical impedance spectroscopy. Results showed that the free-standing composite film with 70 wt% graphene exhibited the lowest charge transfer resistance and the highest charge capacity of about 303 mAh g⁻¹ after 50 cycles, without any noticeable fading.     

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.     

Well-dispersed single-walled carbon nanotube/polyaniline composite films

Single-walled carbon nanotube (SWNT)/polyaniline (PANI) composite films with good uniformity and dispersion were prepared by electrochemical polymerization of aniline containing well-dissolved SWNTs. The results of atomic force microscopy (AFM) and UV-Vis adsorption spectroscopy show that aniline can be used to solubilize SWNTs via formation of donor-acceptor complexes. The electrochemical deposition of SWNT-aniline solutions have been investigated by cyclic voltammetry. The results show that SWNT-based aniline solutions exhibit a drastic increase in peak current within the potential scanning region. The doping effect of SWNTs on PANI films was investigated by electrochemistry and FTIR spectroscopy. The results indicate that the enhanced electroactivity and conductivity of the SWNT/PANI composite films may be due to the strong interaction between SWNTs and PANI, which facilitates the effective degree of electron delocalization.     

Fabrication and electrochemical capacitance of hierarchical graphene/polyaniline/carbon nanotube ternary composite film

A film composed of graphene (GN) sheets, polyaniline (PANI) and carbon nanotubes (CNTs) has been fabricated by reducing a graphite oxide (GO)/PANI/CNT precursor prepared by flow-directed assembly from a complex dispersion of GO and PANI/CNT, followed by reoxidation and redoping of the reduced PANI in the composite to restore the conducting PANI structure. Scanning electron microscope images indicate that the ternary composite film is a layered structure with coaxial PANI/CNT nanocables uniformly sandwiched between the GN sheets. Such novel hierarchical structure with high electrical conductivity perfectly facilitates contact between electrolyte ions and PANI for faradaic energy storage and efficiently utilizes the double-layer capacitance at the electrode–electrolyte interfaces. The specific capacitance of the GN/PANI/CNT estimated by galvanostatic charge/discharge measurement is 569 F g⁻¹ (or 188 F cm⁻³ for volumetric capacitance) at a current density of 0.1 A g⁻¹. In addition, the GN/PANI/CNT exhibits good rate capability (60% capacity retention at 10 A g⁻¹) and superior cycling stability (4% fade after 5000 continuous charge/discharge cycles).     

Outer-specific surface area as a gauge for absolute purity of single-walled carbon nanotube forests

We present a simple approach to estimate the absolute purity of carbon nanotube (CNT) forests based on outer-specific surface area (SSA). The outer-SSA and absolute purity for diverse forms of CNT forests to increased levels of carbonaceous impurities showed similar behavior and revealed a method to distinguish between CNTs and carbonaceous impurities. Furthermore, these experiments showed a direct proportionality between the outer-SSA and absolute purity which led to a simple analytical model to use outer-SSA as a gauge for absolute purity analysis.     

Graphitic carbon nitride nanosheet-assisted preparation of N-enriched mesoporous carbon nanofibers with improved capacitive performance

N-enriched mesoporous carbon nanofibers (NMCNFs) were prepared by an electrospinning technique using graphitic carbon nitride (g-C₃N₄) nanosheets both as sacrificial template and N-doping source. The resultant NMCNF film has a high N-doping level of 8.6 wt% and a high specific surface area of 554 m² g⁻¹. When directly used as the electrode material for supercapacitor, the free-standing NMPCNF film shows a significantly improved capacitive performance including a higher specific capacitance (220 F g⁻¹ at 0.2 A g⁻¹) and a better rate capability (∼70% retention at 20 A g⁻¹) than those of microporous carbon nanofiber film prepared using the same process without using g-C₃N₄ nanosheets (145 F g⁻¹ at 0.2 A g⁻¹ and ∼45% retention at 20 A g⁻¹). Moreover, the NMCNFs show superior stability with only a ∼3% decrease of its initial capacitance after 1000 cycles at a high current density of 10 A g⁻¹. More significantly, the energy density of a symmetrical supercapacitor (SC) based on the NMPCNF film can reach 12.5 Wh kg⁻¹ at a power density of 72 W kg⁻¹.     

Superior performance of non-activated multi-walled carbon nanotube polymer actuator containing ruthenium oxide over a single-walled carbon nanotube

The electrochemical and electromechanical properties of actuators developed using a non-activated multi-walled carbon nanotube (MWCNT)–ionic liquid (IL) gel electrode containing ruthenium oxide (RuO₂) were compared with only-MWCNT and only-single-walled carbon nanotube (SWCNT) based actuators. The double-layer capacitance of the non-activated MWCNT electrode containing RuO₂ was larger than that of the only-MWCNT electrode. The non-activated MWCNT polymer actuator containing RuO₂ surpassed the performance of the only-MWCNT and only-SWCNT actuators in terms of the strain and maximum generated stress. Both MWCNTs and RuO₂ were required to produce large strain and quick response actuators that surpassed the performance of the only-SWCNT polymer actuator and exhibited characteristics sufficient for practical applications (e.g. tactile display).     

Raman intensity measurements of single-walled carbon nanotube suspensions as a quantitative technique to assess purity

A method to assess the purity of single-walled carbon nanotube (SWCNT) bulk samples based on Raman spectroscopy is reported. The new method has higher reproducibility and quantitative precision than those previously used. It consists of measuring the G-band intensity of liquid suspensions of SWCNT samples as a function of solid concentration. A simple equation is proposed in which one of the two adjustable parameters is the SWCNT purity. The method has been applied to a series of samples of similar characteristics, but varying quality. The results are compared to those obtained on the same series of samples using standard analytical techniques, including electron microscopy, thermogravimetric analysis and optical absorption.     

Influence of microstructure on the capacitive performance of polyaniline/carbon nanotube array composite electrodes

A series of polyaniline/carbon nanotube array (PANI/CNTA) composite electrodes are prepared by electrodeposition of PANI onto CNTA electrodes by 100-500 cyclic voltammetry (CV) cycles, with the aim to investigate the influence of microstructure on the capacitive performance of PANI/CNTA composites. The morphology of PANI/CNTA composites varies remarkably with the CV cycles of electrodeposition. The optimum condition is obtained for the PANI/CNTA composite prepared by 100 CV cycles, corresponding to the highest specific capacitance, best rate performance, and longest cycle life, which are much better than that of activated carbon fiber cloth, the PANI electrodeposited on stainless steel substrate, and CNTA electrode. The forming process of the microstructure and its influence on the capacitive performance of PANI/CNTA composites are presented in this paper.     

Enhanced capacitive deionization of graphene/mesoporous carbon composites

Capacitive deionization (CDI) with low-energy consumption and no secondary waste is emerging as a novel desalination technology. Graphene/mesoporous carbon (GE/MC) composites have been prepared via a direct triblock-copolymer-templating method and used as CDI electrodes for the first time. The influences of GE content on the textural properties and electrochemical performance were studied. The transmission electron microscopy and nitrogen adsorption-desorption analysis indicate that mesoporous structures are well retained and the composites display improved specific surface area and pore size distribution, as well as pore volume. Well dispersed GE nanosheets are deduced to be beneficial for enhanced electrical conductivity. The electrochemical performance of electrodes in an NaCl aqueous solution was characterized by cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy measurements. The composite electrodes perform better on the capacitance values, conductive behaviour, rate performance and cyclic stability. The desalination capacity of the electrodes was evaluated by a batch mode electrosorptive experiment and the amount of adsorbed ions can reach 731 μg g(-1) for the GE/MC composite electrode with a GE content of 5 wt%, which is much higher than that of MC alone (590 μg g(-1)). The enhanced CDI performance of the composite electrodes can be attributed to the better conductive behaviour and higher specific surface area.     

Ion irradiation for improved graphene network formation in carbon nanotube growth

Ion irradiation of carbon nanotubes very often leads to defect formation. However, we have recently shown that Ar ion irradiation in a limited energy window of 10–25 eV may enhance the initial cap nucleation process, when the carbon network is in contact with the metal nanocatalyst. Here, we employ reactive molecular dynamics simulations to demonstrate that ion irradiation in a higher energy window of 10–35 eV may also heal network defects after the nucleation stage through a non-metal-mediated mechanism, when the carbon network is no longer in contact with the metal nanocatalyst. The results demonstrate the possibility of beneficially utilizing ions in e.g. plasma-enhanced chemical vapour deposition of carbon nanotubes.     

表面积对煤基电容炭电化学性能的影响

以河北无烟煤为原料,KOH为活化剂,采用化学活化法制备具有高比表面积的煤基电容炭,考察煤基电容炭的比表面积对无机/有机体系下双电层电容器电化学性能的影响。结果表明:随着碱煤比的增加,所制电容炭的比表面积、总孔容和中孔率增加。当碱煤比达到3.5时,所制电容炭的比表面积、总孔容和中孔率分别为3 389 m2/g、2.041 cm3/g、49.9%。可以看出,对于无机/有机体系,在相同的比表面积变化规律下,电容器电化学性能的变化规律略有不同。当碱煤比小于2时,所制电容炭的比表面积小于2 400 m2/g,此时对于无机/有机体系,电容器的比电容变化规律相同,比电容都随比表面积的增大增幅明显。当碱煤比大于2时,所制电容炭的比表面积大于2 400 m2/g,此时随着比表面积的继续增大,对无机体系,电极材料的比电容几乎维持不变,比电容最高可达331 F/g;对有机体系,电极材料的比电容增幅减缓,比电容最高可达192 F/g。当碱煤比为2时,电容炭的比表面积为2 382 m2/g,此时无论对于无机体系还是有机体系,电容器在保持相对较高比电容的同时具有相对较高的电容保持率。由此可知,一定程度上,提高电极材料的比表面积有利于提升超级电容器的电化学性能。制备具有适宜比表面积的电容炭,在得到较高电容性能电容器的同时更能有效控制成本。同时,以煤为原料制备电容炭,可提升煤的附加值,具有很好的市场前景。     

Characterization of single-walled carbon nanotube mats and their performance as electromechanical actuators

Carbon nanotube mats (buckypapers) were prepared from three commercial grades of single-walled carbon nanotubes (SWCNTs) and by two processing variants (i.e. filtration of centrifuged and uncentrifuged dispersions). Material properties such as Young’s modulus, tensile strength, electrical conductivity, electrical capacitance, specific surface area and morphology were investigated and put in relation to the in-plane actuation performance in an aqueous electrolyte (1 M NaCl). A dynamic mechanical analyzer was adapted for actuation strain measurements on the samples under various tensile prestress levels. High SWCNT purity and dispersibility were found to be crucial for preparing dense and strong cohesive mats with good actuation performance.     

Near-infrared photoresponse in single-walled carbon nanotube/polymer composite films

We present a near-infrared photoresponse study of single-walled carbon nanotube/poly(3-hexylthiophene)-block-polystyrene polymer (SWCNT/P3HT-b-PS) composite films for different loading ratios of SWCNT in the polymer matrix. Compared to the pure SWCNT film, the photoresponse [(light current − dark current)/dark current] is much larger in the SWCNT/polymer composite films. The photoresponse is up to 157% when SWCNTs are embedded in P3HT-b-PS while for a pure SWCNT film it is only 40%. We also show that the photocurrent strongly depends on the position of the laser spot with maximum photocurrent occurring at the metal-film interface. We explain the photoresponse due to exciton dissociations and charge carrier separation caused by a Schottky barrier at the metallic electrode-SWCNT interface.     

Preparation and capacitive properties of cobalt-nickel oxides/carbon nanotube composites

In this paper, nickel-cobalt oxides/carbon nanotube (CNT) composites were prepared by adding and thermally decomposing nickel and cobalt nitrates directly onto the surface of carbon nanotube/graphite electrode to form nickel and cobalt oxides. Carbon nanotubes used in this paper were grown directly on graphite substrate by chemical vapor deposition technique. The capacitive behavior of nickel-cobalt oxides/CNT electrode was investigated by cyclic voltammetry and galvanostatic charge-discharge method in 1 M KOH aqueous solutions. The results show that nickel-cobalt oxides/CNT composite electrode has excellent charge-discharge cycle stability (0.2% and 3.6% losses of the specific capacitance are found at the 1000th and 2000th charge-discharge cycles, respectively) and good charge-discharge properties at high currrent density. Additionally, the effect of Ni/Co molar ratio on specific capacitance of the composite electrode was investigated and the highest specific capacitance (569 F g⁻¹ at 10 mA cm⁻²) is obtained at Ni/Co molar ratio = 1:1.