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Highly conductive, mesoporous carbon nanofiber web as electrode material for high-performance supercapacitors
Abstract
Polyacrylonitrile/poly(methyl methacrylate) (PMMA) fibers containing graphene are prepared by the electrospinning method, and hierarchical porous carbon nanofibers (CNFs) are obtained after subsequent heat treatment. The hierarchical porous CNFs have an improved structure and properties because of the increased surface area, unique nanotexture and increased electrical conductivity due to the dispersion of graphene. The carbonized fiber exhibits a high surface area (over 500 m2 g−1) as result of the narrow ultramicro- and mesopore size distributions (centered at approximately 0.7 and 3.7 nm, respectively), and a broad mesopore size distribution ranging from 10 to 50 nm. The hierarchical pore structures are introduced by the evolution of small gas molecules during the decomposition of the PMMA during heat treatment. The highest specific capacitance of the CNFs is 128 F g−1, and the energy densities are 16.0–21.4 W h kg−1 in an aqueous solution and 75.0–58.2 W h kg−1 in an organic electrolyte over a power density range of 400–20,000 W kg−1. Under constant current charging/discharging at 1 mA cm−2 for 100 cycles, the stability of the CNFs in a 6 M KOH aqueous electrolyte decreases by ∼17% compared with the initial specific capacitance value.
... Besides their excellent conductivity, these materials possess superior three-dimensional hierarchical structures with high macropore volume between the fibers (good electrolyte penetration and ion supply), together with micropores/mesopores present on the surface leading to high specific surface areas. Furthermore, freestanding electrode materials can be fabricated without using a binder (reduced internal resistance) [4][5][6][7][8][9], and even flexible lightweight woven materials can be realized with great potential in wearable electronics applications [10][11][12][13][14]. Our study focuses on introducing a novel biobased precursor (chitosan) as a more sustainable alternative to fossil-fuel-based synthetic polymer precursors to fabricate PCNFs. ...
... Carbon nanofibers (CNFs) can be prepared from polymeric precursors using a fiber-forming technique followed by thermal treatment to convert the polymer fibers to conductive carbon. Electrospinning has emerged as a simple, cost-effective way to fabricate fine nanofibrous polymeric networks, typically resulting in final CNF diameters in the 100-500 nm range [1,[4][5][6][7][8][9]11,12,14]. Furthermore, ultrafine CNFs with fiber diameters in the sub-100 nm regime have also been reported using a synthetic polyacrylonitrile precursor [15]. ...
... The porosity of the CNFs can be tailored via numerous methods [1], including (a) using polymer precursor with intrinsic microporosity (e.g. PIM-1) [16], (b) using either a polymeric [4,9,13,15,17,18], and/or a small-molecule porogen included in the electrospinning solution [8,13,19], which degrades and facilitates pore formation during the thermal treatment, and (c) via chemical (e.g. using KOH [20,21], ZnCl 2 [17,19,22]) or physical activation (etching) (e.g. using steam [4,16,19], or CO 2 [19]) mostly as a post-treatment step. In this work, we introduce a method to obtain an ultrafine porous nanoarchitecture using the novel chitosan carbon precursor and poly(ethylene oxide) as a pore-forming agent. ...
Ultrafine porous carbon nanofiber network with ∼40 nm fiber diameter is realized for the first time utilizing a biobased polymer as carbon precursor. A simple one-step carbonization procedure is applied to convert the electrospun chitosan/poly(ethylene oxide) nanofibers to self-N-doped ultrafine hierarchically porous carbon nanofiber interconnected web. The pore formation process is governed by the immiscible nature of the two polymers and the sacrificial character of poly(ethylene oxide) with low carbon yield at the carbonization temperature (800 °C). The obtained porous scaffold has a high specific surface area (564 m² g⁻¹), high micro (0.22 cm³ g⁻¹) as well as meso/macropore volume (0.28 cm³ g⁻¹). Structural analysis indicates high graphitic content and the existence of turbostratic carbon typical for carbon fibers derived from otherwise synthetic polymer precursors. X-ray photoelectron spectroscopy confirms the presence of an N-doped structure with dominating graphitic N, together with a smaller amount of pyridinic N. The prepared electrode exhibits good electrochemical performance as a supercapacitor device. The excellent charge storage characteristics are attributed to the unique ultrafine hierarchical nanoarchitecture and the interconnected N-doped carbon structure. This green material holds great promise for the realization of more sustainable high-performance energy storage devices.
... Hence, porous carbon nanofibers with excellent mesopore volume were prepared using physical etching of selective polymer from polymer-polymer blends of polyacrylonitrile (PAN)/polyvinylpyrrolidone (PVP), PAN/poly methyl methacrylate (PMMA), and PAN/polyacrylic acid (PAA). [4][5][6][7][8] The enhanced specific capacitance of these porous carbon nanofiber-based electrodes was attributed to the improved surface area and mesopore volume. Alternatively, the specific capacitance of CNFs was also improved by adding high theoretical capacitance metal oxides such as Co 3 O 5 , MnO 2 , RuO 2 , V 2 O 5 and conductive polymers. ...
Carbon nanofiber-based electrodes are generally embedded with either metal oxides or two-dimensional materials to enhance their specific capacitance and rate performance. For the first time, a flexible carbon nanofiber electrode consisting of metal oxide (RuO 2 ) and two-dimensional MXene was prepared to realize the synergetic effect on the electrochemical performance. This ternary composite electrode was prepared by electrospinning RuO 2 , and MXene dispersed polyacrylonitrile precursor solution, followed by thermal treatment. The distribution of RuO 2 nanoparticles and delaminated MXene sheets within a carbon nanofiber matrix was examined using X-ray diffraction and transmission electron microscopy, while morphological analysis was carried out using scanning electron microscopy. The electrode with pseudocapacitive RuO 2 and layered MXene facilitated charge storage by faradic reactions and intercalation of electrolyte ions. Electrochemical studies demonstrated that the prepared ternary composite electrodes exhibit a specific capacitance of 322 F g ⁻¹ with a capacitance retention of 90% after 2500 cycles at 1 A g ⁻¹ . Additionally, the ternary composite showed an excellent rate capability with a minimal drop in capacitance when the current density was varied from 2 A g ⁻¹ to 10 A g ⁻¹ .
... The optimized pore structure is required to obtain the high specific capacitance since CNFs store and release energy via ions adsorption-desorption on the surface of the electroactive sites. Adding some polymers such as polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polyaniline (PANI), and polymethylmethacrylate (PMMA) into polyacrylonitrile (PAN) polymer provides a higher surface area with a welldeveloped pore structure, increasing the electrochemical performance of SCs [11,[14][15][16][17]. Another efficient strategy is introducing heteroatom (i.e., N, S, B, or F) dopants into the carbon matrix for designing SC electrodes for enhanced energy storage performance [12,[18][19][20][21]. Besides, heteroatom dopants, especially nitrogen and sulfur, into CNFs can increase not only their wettability due to their electron donor properties but also contribute an additional pseudocapacitive effect by reversible faradic reactions [22][23][24][25][26][27]. ...
Herein, using thiourea is a simple and effective approach to produce the unique structure constructed by N and S dual-doped carbon nanofibers. The surface porosity is optimized by changing the thiourea amount in the polymer solution. The optimized N/S-CNF5, which the weight percentage of thiourea to polyacrylonitrile is 5, has a high specific surface area (144.2 m² g⁻¹) and rich content of heteroatoms (N-4.66 at% and S-0.11 at.%), respectively. Because of these unique features, N/S-CNF5 demonstrates a large gravimetric-specific capacitance (312 F g⁻¹ at 10 mV s⁻¹ and 225 F g⁻¹ at 1 A g⁻¹). The N/S-CNF5 electrode represents in the two-electrode system with a high specific capacitance of 160 F g⁻¹ at 1 A g⁻¹ and shows a remarkable rate of performance (87.5% retention) even at 5 A g⁻¹. Moreover, the symmetrical supercapacitor device (N/S-CNF5//N/S-CNF5) delivers specific energy of as high as 5.5 Wh kg⁻¹ with a specific power of 250 W kg⁻¹. Also, the device’s cycling ability is 78.3% even after 30 000 cycles at 1 A g⁻¹. This strategy can be feasible to explore more dual heteroatom-doped carbon nanomaterials for a wide range of electrochemical applications.
... hollow, core-shell, multi-channel) of carbon nanofibers can be tuned and designed by easily adjusting polymer blends or using additives [101][102] . The thermolabile polymers can be serveved as sacrificial polymer and decomposed during carbonization to create pores or hollow structure, such as PVP and polymethylmethacrylate (PMMA), which allows to design nanofibers with a large surface area and porous structure [103][104][105][106] . The porosity provides channel for quick transfer of electrolyte ions thus improving the charge storage capacities and rate capability. ...
... hollow, core-shell, multi-channel) of carbon nanofibers can be tuned and designed by easily adjusting polymer blends or using additives [101][102] . The thermolabile polymers can be serveved as sacrificial polymer and decomposed during carbonization to create pores or hollow structure, such as PVP and polymethylmethacrylate (PMMA), which allows to design nanofibers with a large surface area and porous structure [103][104][105][106] . The porosity provides channel for quick transfer of electrolyte ions thus improving the charge storage capacities and rate capability. ...
The construction of flexible supercapacitors with high electrochemical performance and excellent mechanical properties to power flexible electronics and sensors is very important. Freestanding electrodes play a crucial role in flexible supercapacitors, and carbon has been widely used in this role because of its high electronic conductivity, tunable porosity, adjustable surface area, excellent mechanical properties, low density and easy functionalization. It is also abundant and cheap. Recent progress on the fabrication of freestanding carbon electrodes based on various carbon materials for use in flexible supercapacitors is summarized, and remaining challenges and future opportunities are discussed.
... In 6 M KOH, the developed material showed specific capacitance of 263.7 F/ g and cycling stability for energy storage with 86.9% retention ratio. Kim et al. 154 used a mesoporous CNF web for highperformance supercapacitor applications. The developed carbonized fiber showed a high surface area of ∼500 m 2 g −1 . ...
Carbon nanofibers (CNFs) display colossal potential in different fields like energy, catalysis, biomedicine, sensing, and environmental science. CNFs have revealed extensive uses in various sensing platforms due to their distinctive structure, properties, function, and accessible surface functionalization capabilities. This review presents insight into various fabrication methods for CNFs like electrospinning, chemical vapor deposition, and template methods with merits and demerits of each technique. Also, we give a brief overview of CNF functionalization. Their unique physical and chemical properties make them promising candidates for the sensor applications. This review offers detailed discussion of sensing applications (strain sensor, biosensor, small molecule detection, food preservative detection, toxicity biomarker detection, and gas sensor). Various sensing applications of CNF like human motion monitoring and energy storage and conversion are discussed in brief. The challenges and obstacles associated with CNFs for futuristic applications are discussed. This review will be helpful for readers to understand the different fabrication methods and explore various applications of the versatile CNFs.
... [10] HCs can provide high pseudocapacitance, in addition to the high capacitance provided by the electrical double layer at the supporting electrode surface [11]. EDLCs employ various carbon materials such as activated carbon [12], carbon nanotubes [13], carbon nanofibers (CNFs) [14], and graphene [15] as electrodes because their large specific surface area provides a high capacity, and their electrochemical stability provides a long service life. However, EDLCs employing carbon materials present the disadvantage of a low energy density. ...
Concerns associated with global warming and the depleting reserves of fossil fuels have highlighted the importance of high−performance energy storage systems (ESSs) for efficient energy usage. ESSs such as supercapacitors can contribute to improved power quality of an energy generation system, which is characterized by a slow load response. Composite materials are primarily used as supercapacitor electrodes because they can compensate for the disadvantages of carbon or metal oxide electrode materials. In this study, a composite of oxide nanoparticles loaded on a carbon nanofiber support was used as an electrode material for a hybrid supercapacitor. The addition of a small amount of hydrophilic FeN@GnP (Fe− and N−doped graphene nanoplates) modified the surface properties of carbon nanofibers prepared by electrospinning. Accordingly, the effects of the hydrophobic/hydrophilic surface properties of the nanofiber support on the morphology of Co3O4 nanoparticles loaded on the nanofiber, as well as the performance of the supercapacitor, were systematically investigated.
... [5] HCs can provide high pseudocapacitance, in addition to the high capacitance provided by the electrical double layer at the supporting electrode surface [6]. EDLCs employ various carbon materials such as activated carbon [7], carbon nanotubes [8], carbon nanofibers (CNFs) [9], and graphene [10] as electrodes because their large specific surface area provides a high capacity and their electrochemical stability provides a long service life. However, EDLCs employing carbon materials present the disadvantage of a low energy density. ...
Concerns associated with global warming and the depleting reserves of fossil fuels have highlighted the importance of high-performance energy storage systems (ESSs) for efficient energy usage. ESSs such as supercapacitors can contribute to improved power quality of an energy generation system, which is characterized by a slow load response. Composite materials are primarily used as supercapacitor electrodes because they can compensate for the disadvantages of carbon or metal oxide electrode materials. In this study, a composite of oxide nanoparticles loaded on a carbon nanofiber support was used as an electrode material for a hybrid supercapacitor. The addition of a small amount of hydrophobic Fe- and N-doped graphene nanoplates modified the surface properties of carbon nanofibers prepared by electrospinning. Accordingly, the effects of the hydrophobic/hydrophilic surface properties of the nanofiber support on the morphology of Co3O4 nanoparticles loaded on the nanofiber, as well as the performance of the supercapacitor, were systematically investigated.
... A blend of synthetic polymer (PAN), [68] natural polymer (lignin), [70] and petroleum polymer (pitch) [74] was used to enhance the carbon contribution in CNF. Other polymer blends, such as PAN/PVP, [77] PAN/ PMMA, [78] and PI/PVP, [79] have also been used in varying ratios. These polymer blends provide greater control over the pore structure, surface area, and other properties of the CNF compared with a single polymer. ...
Carbon nanofibers derived from electrospun precursors show great promise for electronic applications owing to their flexibility, conductivity, high surface area, and open structure. The integration of metal oxides and sulfides in carbon nanofibers, rather than using them with other binders, eliminates many problems caused by poor adhesion, nanomaterial agglomeration, excess mass contributed by inactive binders, and low conductivity of embedded active materials. The engineering of electrospun fibers with novel morphologies, such as core-shell, hollow, or porous structures, and the use of decorated carbon nanofibers (e.g., by electrodeposition or co-precipitation) are discussed in this review. Representative schematic illustrations of the lithium-storage mechanism for these binder-free electrodes are presented. We describe how the electrospinning technique can offer a cost-effective strategy for fabrication of lightweight lithium-ion batteries with high capacity and excellent bendability. This review presents the fascinating morphologies of these specially designed carbon nanofiber electrodes, which enhance the electrochemical performance of metal oxides and sulfides, illustrating their enormous potential for use in wearable electronic devices and hybrid electric vehicles.
... Xue et al. prepared cross-linked carbon nanofibers (CLCNF) by directly carbonizing electrospun polyacrylonitrile (PAN) nanofibers and reported the energy density 5.13 Wh/kg and power density 579 W/kg [4]. Kim et al. demonstrated the preparation of highly conductive mesoporous carbon nanofiber web as electrode material prepared from PAN and PMMA by electrospinning and reported energy density 16 Wh/kg and power density 400 W/kg [5]. Mesoporous graphitic carbon fibers prepared by electrospinning with energy density 2.82 Wh/kg and power density 720 W/kg reported by Dong et al. [6]. ...
In this paper, we report the fabrication of activated carbon nanofibers/cobalt ferrite (CNF/CoFe2O4) composites by electrospinning and hydrothermal methods for comparative study of electrochemical properties. The structural, morphological and compositional analyses of the synthesized composites were examined using x-ray diffraction, scanning electron microscopy and energy dispersive x-ray spectroscopy. CNF/CoFe2O4 electrodes were investigated for electrochemical behavior using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge-discharge (GCD). The results showed that hydrothermally synthesized CNF/CoFe2O4 composite exhibited the specific capacitance 188.36 Fg−1, whereas electrospun CNF/CoFe2O4 composite resulted the specific capacitance 106.59 Fg−1 at lowest current density 0.5 Ag−1. 80% capacitance retention of CNF/CoFe2O4 prepared by hydrothermal as compared to 60% capacitance retention of CNF/CoFe2O4 prepared by electrospinning. These results concluded that CNF/CoFe2O4 electrode obtained by hydrothermal exhibited comparatively excellent electrochemical performance and found its suitability as electrodes for supercapacitors.
... Despite a much lower SSA, CCNF-0.75 even outperforms pure CB in the specific capacitance (166 F g −1 , as shown in Fig. S12e), which should be attributed to the existence of extra PC. It is worth mentioning that the CB-based carbon fibers show a superior capacitance to the CB/graphene hybrid fibers [43], all-graphene fibers [44], CNT yarn [45], carbon dots/graphene microfibers [19], and some nanocarbons with much the same SSA [8,[46][47][48][49][50], as listed in Table S2. ...
Construction of functional materials using low-dimensional carbons has attracted tremendous attention in the field of energy storage devices. Herein, porous carbon black (CB) is used as the dominant building unit to construct porous sub-micron carbon fibers by electrospinning and pyrolysis with polyacrylonitrile (PAN)-based pyrolytic carbon as the binder. Inheriting abundant pores and surface area from the porous CB, the resultant CB-based sub-micron fibers present considerable porosity and specific surface area. The PAN-based pyrolytic carbon endows the CB-based sub-micron carbon fibers with a considerable quantity of N/O-containing surface. CB content plays a crucial role in improving thermal stability, flexibility, and conductivity of the resultant sub-micron carbon fibers. The CB-based sub-micron carbon fibers present a considerable specific capacitance, excellent cycling stability and can be used electrodes for flexible supercapacitors.
... Metal-air batteries necessitate an oxygen-reduction reaction (ORR) process in the cathode, using nanofiber mats produced, e.g., by electrospinning or a sol-gel route [107,108]. One of the most important points to optimize the ORR activity is a high specific surface area [109,110]. Hence, many studies aim at introducing nanopores in the nanofiber surface. To produce porous CNFs, a template strategy is regularly utilized with different inorganic materials like metals or metal oxides (Sn, ZnO 2 , CaCO 3 , Al 2 O 3 , SiO 2 , etc.). ...
The field of carbon nanofibers has been growing in terms of technological development and seeking attention because of their dominant chemical properties, mechanical strength, and electrical conductivity. Catalytic and electrospinning techniques are currently the conventional methods for fabrication of carbon nanofibers in a two-step process that includes stabilization and carbonization of polyacrylonitrile (PAN) nanofibers, respectively. Recently, the industrial and medical sectors dealing with nanofibrous materials are not having ample options but to accept the use of already approved materials which are quite expensive and lack the flexibility in manipulating their surface and chemical properties for specific applications. To overcome these limitations, carbon nanofibers are being validated for their multifunctional role in various forms. This article reviews the recent advancements in the fabrication of carbon nanofibers and additionally pointing out their significance for applications in the industrial and biomedical sector for their potential role in the future. In this article, we explicitly focus on the recent breakthroughs in the field of carbon nanofibers, especially in the area of their commercial applications. Our goal is to depict ways for enhancing the chemical and structural properties of these nanofibers and providing beneficiary, low-cost alternatives to the currently available materials in the medical field as well as the industrial area.
In this work, the content of lignin, pitch, and PAN as well as the preparation process would be systematically controlled in order to prepare carbon nanofibers (CNFs) with cross‐linked structure, high specific surface area, and good flexibility. The evolution of nanofibers with different lignin contents during stabilization and carbonization were explored, and the properties of the resultant CNFs as supercapacitor self‐supported electrodes were compared. The results indicated that with the increase of lignin content, not only cross‐linked structures were introduced in CNFs, but also the flexibility were obviously improved, accomplishing for supercapacitor self‐supported electrodes. Moreover, CNFs with different content of lignin varied in fiber morphology and microstructure, harvesting developed porous structure in CNFs. PPL3‐CNF prepared with adding lignin at a mass ratio of 3/7 into a concentration of 10 wt.% pitch/PAN solution presented the highest specific surface area of 949 m2 g ⁻¹ , exhibiting an excellent specific capacitance of 190.7 F g ⁻¹ at 0.2 A g ⁻¹ .
Porous carbon fibers are promising cathodes for zinc-ion hybrid supercapacitors (ZHSs) owing to their abundant active sites, great conductivity, and stable physical and chemical properties. However, designing a proper preparation technique to regulate the microstructure of carbon fibers still remains a great challenge. Here, a polyvinylpyrrolidone/po-lyacrylonitrile (PVP/PAN)-derived porous carbon fiber is developed via the PVP/PAN blend electrospinning and hydrothermal selective PVP removal strategy. The hydrothermal selective PVP removal strategy can effectively avoid a cross-linking between PVP and PAN during the traditional stabilization at air atmosphere. In PVP/PAN-derived porous carbon fiber, the sufficient micropores provide abundant space for the Zn2+ storage, whereas the proper mesopores contribute to the fast ion transfer. These hierarchical porous structures endow ZHSs with high specific capacity and high-rate performance. The ZHS assembled with the optimal PVP/PAN-derived porous carbon fiber (PVP-PANC-0.8) displays an outstanding specific capacity of 208 mAh·g−1, high rate capability (49.5%) from 0.5 to 5 A·g−1, and 72.25% capacity retention after 10,000 cycles at 0.5 A·g−1.
One-dimensional (1D) mesoporous nanofibers (NFs) have recently attracted tremendous interest in different fields, in virtue of their mesoporous structure and 1D geometry. However, conventional electrospinning, as a versatile approach for producing 1D nanostructures, can only fabricate solid NFs without pores or with a microporous structure. In this review, we focus on the extensions of the electrospinning technique to create 1D mesoporous fibrous structures, which can be categorized into: (i) foaming-assisted, (ii) phase separation-induced, (iii) soft-templated, and (iv) monomicelle-directed approaches. Special focus is on the synthesis strategies of 1D mesoporous NFs, and their underlying mechanisms, with looking into the control over pore sizes, pore structures, and functionalities. Moreover, the structure-related performances of mesoporous NFs in photocatalysis, sensing, and energy-related fields are discussed. Finally, the potential challenges for the future development of 1D mesoporous fibers are examined from the viewpoint of their synthetic strategies and applications.
Four extended electrospinning techniques to construct mesoporous nanofibers were summarized and the structure related performances in photocatalysis, sensors, and energy related fields were highlighted.
Carbonaceous materials are attractive active materials for the manufacture of flexible electrochemical double-layer capacitors (EDLCs) because of their high electrical conductivity, large surface area, and inherent resilience against deformation. However, compared to pseudocapacitors, which store electrochemical energy via faradaic redox reactions, EDLCs generally exhibit inferior energy density. One potential approach to addressing this issue is to incorporate highly porous and electrically conductive materials into carbonaceous material-based EDLCs. In this paper, we present a hybrid electrode consisting of a conductive metal–organic framework (c-MOF) with high electrical conductivity and unique porous structure combined with a mat of aligned carbon nanofibers (ACNFs). Its highly ordered structure facilitates electronic/ionic transport, increasing the areal capacitance by up to 3.9 times compared to randomly-oriented carbon nanofibers (RCNFs). An additional increase in areal capacitance (+64%) is achieved by introducing c-MOF (RCNFs: 25.4 mF cm⁻²; ACNFs: 98.7 mF cm⁻²; c-MOF/ACNF: 161.8 mF cm⁻²). Additionally, an ACNF mat exhibits excellent mechanical flexibility and electrochemical reliability, making it highly suitable for the assembly of freestanding flexible supercapacitors. By optimizing the electrochemical performance of c-MOF/ACNF and its suitability for utilization in flexible energy storage systems, this study presents a promising avenue for the practical implementation of c-MOF-based supercapacitors.
Supercapacitors (SCs) are attracting a significant amount of interest as energy storage devices owing to their higher specific power, rapid charging–discharging rate, and prolonged cyclic stability. Carbon-based materials are used frequently in SCs because of their excellent electric conductivity, stable chemical properties, and low cost. Electrospun polyacrylonitrile (PAN)-based carbon nanofibers (CNFs) have attracted much interest as they perform well electrochemically, have a large surface area, and show substantial mechanical characteristics; as well as having a high carbon yield among all polymer PAN. In this paper, an extensive review of the synthesis, characterization, and electrochemical performance of electrospun PAN CNFs is presented. An overview of the electrospinning procedure and properties of PAN CNFs that make them suitable for SC applications is presented. Various characterization methods, including transmission electron microscopy, scanning electron microscopy, x-ray diffraction, Raman spectroscopy, and surface area analysis, have been carried out to evaluate the morphological, structural, and surface properties of PAN CNFs. The review also highlights the recent advances in modification and functionalization to enhance their electrochemical performance, including doping, surface functionalization, and hybridization. Galvanostatic charge–discharge experiments, cyclic voltammetry, and electrochemical impedance spectroscopy have been employed for electrochemical characterization. Finally, a comparative study between various carbon-based and electrospun PAN CNF electrode materials for SCs has been conducted. The review is concluded by discussing the challenges, opportunities, and possible future trends in the development of high-performance electrode material. This comprehensive review provides valuable insightful information on the design and optimization of electrospun PAN CNF electrode materials for SC applications.
In order to solve the problems of high cost and high brittleness of commercial carbon fiber paper, a low-cost mass production method of carbon fiber paper for flexible super capacitor was proposed. The dispersant CMC-Na is utilized to achieve uniform dispersion of chopped carbon fiber in a water system through ultrasonic dispersion. Sheath-core composite (PE/PET) fiber not only enhances the tensile strength of CFP but also consolidates the electrode network structure formed based on carbon fiber structure. The CFP-3 electrode, impregnated with 3 % AC phenolic resin, exhibits excellent mechanical and electrochemical properties. SEM images reveal that AC is deposited on each carbon fiber and that the CFP-3 electrode retains its three-dimensional structure (with a porosity of 71.2 %), providing an effective permeation path for electrons (with an electrical conductivity of 0.871 S m⁻¹). The CFP-3 electrode can restore its original shape after folding and bending without damage. Electrochemical tests demonstrate that the CFP-3 electrode has a high areal capacitance of 507.2 mF cm⁻² at a current density of 0.5 mA cm⁻². At a current density of 10 mA cm⁻², the capacitance retention rate of the CFP-3 electrode is 96.1 % after 5000 charge-discharge cycles, owing to the well-interconnected structure of the carbon fiber paper. Furthermore, when used as a direct electrode, CFP exhibits excellent stability. Most notably, the cost of producing the CFP-3 electrode (0.0314 m²) is only $0.195, significantly lower than that of commercial products, excluding equipment, utilities, and labor costs. This research provides valuable insights for the low-cost, large-scale production of paper-based flexible supercapacitors.
Supercapacitors are outstanding electrochemical energy storage devices with high power density, quick charge and discharge and long cycle life. A well-designed structure can significantly increase its electrochemical performance as electrode materials. Carbon nanofibers (CNFs) made by electrospinning technique feature a one-dimensional nanostructure, which can provide directional electron transfer pathways and reduce the internal resistance of materials. This article reviewed the design approaches for one-dimensional nanostructured electrode materials produced from CNFs for supercapacitors, focusing on porous structure design, hollow structure design, surface functional group structure design and core-shell structure design. The porous and hollow structural designs could improve the contact area between electrode and electrolyte, allowing for faster electron/ion transport. Surface functional group structure design had the potential to improve the surface chemical properties of electrode materials, therefore enhancing their capacitance characteristics. The core-shell structure design might result in layered channels, and the diverse components of the core and shell could work together to increase the conductivity and structural stability of electrode materials. The preparation methods and structural properties of these CNF electrode materials with different structural designs were highlighted, as well as their future development.
Porous carbon nanofibers (PCNFs) have been the hotpot material for supercapacitor due to their porous structure, outstanding conductivity, excellent electrochemical properties, and high specific surface area. The template method is a facile approach to prepare PCNFs through blending a thermally decomposable substance, subsequently heating treatment. High amylose starch (HAS) is a natural carbohydrate including carbon, hydrogen and oxygen elements. Herein, a simple template method utilizing HAS as the sacrificial polymer to prepare porous carbon nanofibers with high specific surface areas has been reported. The resulted carbon nanofibers have a hierarchical micro/meso porous structure with high level of microporous pores, more importantly, their specific surface area can reach 1204 m² g⁻¹. The electrochemical performances of PCNFs electrodes are studied using a three-electrode system and button-type devices. The specific capacitance of carbon nanofiber electrode is 344 F g⁻¹ at 1.0 A g⁻¹ when 20 wt% HAS is added. The cycling durability of corresponding device is 99.9% capacitance retention after 10000 cycles. And the maximum energy density of 12 Wh kg⁻¹ is obtained at a lower power density of 125 W kg⁻¹. As a green natural material, HAS may provide a low-cost solution to prepare high-performance carbon nanofibers for energy storage applications.
Free-standing carbon nanofibers are crucial electrode materials for supercapacitors. Herein, nanocube-embedded porous carbon nanofibers (P-CNFs) from manganese(II) chloride/cobalt(II) chloride/iron(III) nitrate-polyacrylonitrile (Mn/Co/Fe@PAN) were fabricated using electrospinning followed by a thermal treatment. The self-formation of uniformly distributed nanocubes over the carbon nanofiber was confirmed by scanning electron microscopy (SEM). P-CNF//P-CNF-based supercapacitors (SCs) using flexible and free-standing electrodes without any binder demonstrated a high mass specific capacitance of 107.4 F g−1 at 1 A g−1 and a good specific energy of 3.68 Wh kg−1 in 1 M H2SO4 electrolyte. Even at a high specific power, 2000 W kg−1, it retained a high specific energy of 3.18 Wh kg−1 Moreover, the supercapacitor cell exhibited a remarkable rate capability with a retention of 85.5% from 1 to 8 A g−1 and it possessed a prominent cycle stability of 97.9% after 50,000 cycles, which are really significant values reported in the literature for CNF-based electrodes to date. The high electrochemical cyclability and stability of P-CNFs originated from a combination of hierarchical porous structure of nanofibers with decoration of metallic nanoparticles. This unique nanocube structure provided more electrochemically active sites which are conductive towards electrochemical reactions. The reaction kinetics were also studied and the percentage of capacitive- and diffusion-controlled capacitance were found as 88% and 12%, respectively. As a result, addition of ternary metallic salts plays a significant role in improving ultrastable energy storage systems.
Carbon nanofibers (CNFs) with high specific surface area and flexible lap structure are highly desirable for numerous applications such as adsorption films, supercapacitors, heat dissipation elements, and composites. In this work, CNFs were prepared using two major categories of pitches, isotropic pitch (IP) and mesophase pitch (MP), as raw materials to compare their molecular structure effects on the morphology and properties of CNFs. The analysis of scanning electron microscopy results found that some fusions among nanofibers easily formed in IP-derived electrospun nanofibers (IP-SNFs) while an independent and smooth nanofiber morphology were observed in MP-derived electrospun nanofibers (MP-SNFs). Besides, composed of high aromatic molecules content and appropriate aliphatic components, MP-SNFs showed a mitigating exothermic reaction and MP-CNFs exhibited higher specific surface area, conductivity and thermal diffusion coefficient. While with too abundant aliphatic components in IP, there was a violent exothermic reaction of IP-SNFs during the stabilization process, endowing the corresponding IP-CNFs with poor performances. Therefore, thermal behavior of SNFs varied with the molecular structure differences of IP and MP, which had a significant influence on the microstructure and properties of their CNFs.
Triple-layered boron-containing carbon nanofibers (CNFs) with hollow channels (PPMPB) are fabricated via step-by-step electrospinning for high-performance freestanding supercapacitors. Polyacrylonitrile (PAN (PAN)-based CNFs in the first layer are chosen as the support layer material because of their excellent chemical stability and electrospinnability. The well-developed hollow channels provided fast ion diffusion in the second layer of PAN/poly(methyl methacrylate) (PMMA)-based CNFs. The surface boron functional groups constituting the third layer contribute to the pseudo-capacitance. The symmetric supercapacitor of the PPMPB electrodes delivers a maximum specific capacitance of 180 Fg⁻¹ at 1 mAcm⁻², a high energy density of 22.38 Whkg⁻¹ at a power density of 400 Wkg⁻¹, and an excellent retention rate of 96% after 10,000 cycles in aqueous solution. The excellent electrochemical performance is attributed to the unique sandwich nanostructure with a three-layer structure, in which the factors representing the electrochemical properties of each layer do not interfere with each other. Therefore, a moderate amount of boron and the high surface area of the triple-layer structured PPMPB can be fully utilized as an excellent conductive network and electroactive sites, which is expected in a high-performance supercapacitor electrode.
Over the past few decades, carbon nanofibers (CNFs) have attracted attention in terms of technological development due to their remarkable mechanical and chemical characteristics as well as electrical conductivity. Currently, CNFs are being fabricated over electrospinning and catalytic approaches in two steps including stabilization and carbonization of polyacrylonitrile (PAN) nanofibers, respectively. Lately, the medical and industrial sectors dealing with quite expensive nanofibrous materials which have less flexibility in the functionalization of their chemical and surface characteristics for specific applications. To eliminate these limitations, CNFs are being multi-functionalized in diverse forms. This article reviews the recent progress in the design and synthesis of CNFs and their industrial and biomedical applications. In this article, the main focus is to review the recent breakthroughs in the field of CNFs, the modification of structural and chemical characteristics of CNFs used for various commercial applications. Furthermore, a brief summary is provided for various inexpensive substitutes for the currently existing materials.
The versatile electrospinning technique is scalable and suitable to fabricate highly conducting freestanding carbon nanofiber composite electrodes for energy storage devices. Freestanding/flexible electrodes hold enormous potential for use in wearable electronic devices. Carbon-yielding polymers and the optimal use of sacrificial polymers, metal oxides, and sulfides retain the flexibility and enhance the surface area and pseudocapacitance of electrodes. Both as-prepared electrospun fibers and carbonized nanofibers are compatible with surface decoration via various chemical and electrochemical routes. Metal oxides/sulfides with various morphologies, such as nanocones and nanosheets, can be grown on the carbon nanofibers or on the as-prepared electrospun fibers using chemical synthesis methods such as electrodeposition, hydrothermal processes, and chemical impregnation to enhance the pseudocapacitance of the electrodes. Similarly, the deposition of metal organic frameworks on as-prepared electrospun fibers embellishes these fibers with nanostructures of specific morphologies such as dodecahedral and spindle-shaped structures. Under optimal conditions, these morphologies do not hamper the flexibility of the fibers, and binders are not required to retain them or maintain the electrode integrity. The engineering of electrodes with various morphologies and process parameters is presented systematically. Electrospinning-derived electrodes that have demonstrated significant electrochemical performance are highlighted and critically analyzed, and the energy storage mechanisms of these supercapacitors are described in detail.
Sandwich-structured carbon nanofiber/MnO2/carbon nanofiber composites with a triple layer are fabricated by electrospinning. The optimized sandwich-structured composite electrodes exhibit the maximum specific capacitance of 220 F/g at 1 mA/cm², a high energy density of 24.63 Wh/kg at a power density of 400 W/kg, and an excellent retention rate of 94% after 10,000 cycles. The stable spatial distribution of MnO2 nanoparticles between the upper and lower carbon nanofiber webs allowed full use of the well-preserved MnO2 nanoparticles in the interlayer as electroactive sites, providing better electrochemical performance. Furthermore, the hollow core present in the interlayer serves as an excellent conducting network, providing a short ion diffusion path for both ions and electrons. In addition, the asymmetric supercapacitor shows excellent cycling behavior between 0 and 1.4 V and a large energy density of 44.3Wh/kg at a power density of 400 W/kg, showing great potential in the development of energy storage devices with high energy density for practical applications.
Due to their superior properties, nanofibers are preferred in many fields, especially in tissue engineering, drug delivery, seed coating material, cancer diagnosis, lithium-air battery, optical sensors and air filtration. Compared to conventional fibrous structures, nanofibers are lightweight onedimensional nanomaterials with diameters in the range of tens to hundreds of nanometers, controllable pore structures, three-dimensional interconnected structures, high surface-to-volume ratios, and high mass transport properties which make them ideal for use in different applications. Many methods are used for production of nanofibers. However, centrifugal spinning is a technique that allows very fast nanofiber production. Besides, in this technique, wider range of polymers and solvents can be used and nanofibers with high porosity can be obtained by using different solution and process parameters. Diameter, total surface area, porosity and pore size of nanofibers affect performance. In addition, using nanofillers is a promising method to improve the properties of the fibers. The incorporation of graphene into the fibers improves mechanical, electrical, and thermal, properties of the fibers. In this study, polyacrylonitrile / polymethylmethacrylate fibers containing different ratios of graphene were produced by centrifugal spinning technique. Nanofibers containing 3, 5 and 7 wt.% graphene based on polymer weight were produced. Morphological and structural characterization was carried out using SEM, TEM and FTIR. The effect of graphene on nanofiber diameters and the distribution of graphene in the nanofibers have been studied. The morphology of the fibers prepared in nanocomposite structure was examined using SEM. The effect of graphene on nanofiber morphology was also determined by TEM. While nanofibers containing 3, 5 wt.% graphene had uniform morphology, it was observed that graphene affected fiber formation. When 7 wt. % graphene was used, bead formation was observed. In addition, increasing graphene content to 7 wt.% caused a decrease in average fiber diameters.
Here, the treated ultra-fine needle coke particles (UNCs) are introduced in hierarchical porous ultra-fine carbon fibers by electrospinning and thermally treatment process of two immiscible polymers and UNCs precursor. The structure, morphology and electrochemical performance of the ultra-fine carbon fibers derived from polyacrylonitrile (PAN)/polymethylmethacrylate (PMMA)/UNCs are explored in detail. As a result, when the mass ratio of PAN to PMMA reaches 6: 4, the ultra-fine carbon fibers derived from PAN/PMMA/UNCs display a high surface area of 919.3 m² g⁻¹, a suitable mesoporous structure of meso/micro = 1.59. and exhibit a remarkable specific capacity (387.2 F g⁻¹ at 0.5 A g⁻¹) and excellent power performance. Furthermore, a comprehensive electrochemical performance of symmetrical supercapacitors was obtained: prominent energy density (27.87 Wh·kg⁻¹ at 489 W kg⁻¹) and ideal cyclic stability (97.5% capacity retention after 10,000 cycles at 1 A g⁻¹). In addition, hierarchical porous ultra-fine carbon fibers derived from blend polymer and needle coke with high degree of graphitization, which provide a potential optional application for served as binder-free electrodes for electrochemical energy storage devices.
Electrochemical capacitors and supercapacitors represent the typical energy storage devices possessing rapid charge/discharge kinetics and a high power density (Zhu et al. in Science 332:1537–1541, 2011; Lang et al. in Nat Nanotechnol 6:232–236, 2011; Simon et al. in Science 343:1210–1211, 2014; Sheberla et al. in Nat Mater 16:220–224, 2017). In general, supercapacitors can be classified as the electrochemical double-layer capacitors (EDLCs) or pseudocapacitors according to the energy storage and conversion mechanisms.
Apart from the conventional nanostructures mentioned in the previous chapters, the 1D mesoporous inorganic nanomaterials are designed with certain special constructions for multifarious functional applications, such as core–shell, ordered mesoporous, hierarchically mesoporous structures and so on. This chapter is dedicated to the methods and techniques which have been used to afford the synthesis of these special 1D mesoporous inorganic nanostructures.
The 1D nanomaterials, which may exist as wires, fibers, belts, tubes or rods, arouse wide attention because they are significant in fundamental scientific research and may potentially be applied in the field of nanotechnology (Li and Xia in Nano Lett 4:933–938, 2004; Tian et al. in Nature 449:885–889, 2007; Zheng et al. in Science 333:206–209, 2011).
Electrospinning has emerged as a versatile and promising technique to synthesize nanofibres. With increasing demand of nanotechnology, electrospinning has gained more attention due to its versatile application in various fields. Scientists have incorporated various nanomaterials as nanofillers in the polymeric matrix to enhance the properties of nanofibres according to their specific applications. Among these nanofillers, graphene has gained extensive interest for researchers, as a multifunctional molecule associating different unique properties like high mechanical strength, electrical conductivity, flexibility, conductivity and optical transparency. These desirable properties make graphene a superior material than CNTs and other conducting nanoparticles. The graphene-based polymeric nanofibres have opened new opportunities for diverse applications of nanofibres in different walks of life. This chapter aims to describe an overview of progress of graphene-based electrospun nanofibres and their applications in various fields including biomedical, chemical, defence and environmental applications. The historical overview and fundamentals of electrospinning, graphene and its properties as nanofiller as well as the applications of graphene-based electrospun nanofibres in different fields are discussed. The limitations and future developments of electrospinning and graphene-based electrospun nanofibres that can be made are also presented.
Supercapacitors (SCs) with the advantages of high power density, fast charge/discharge and no memory effect have been regarded as potential energy storage devices. Mo-based materials have been extensive used as active electrode materials in pseudocapacitors due to their high theoretical specific capacities, eminent electrochemical activities, as well as highly reversible redox reactions. However, the serious self-aggregation and huge volume change of Mo-based materials can cause a dramatic capacity decay during the electrochemical process. Carbon nanofibers (CNFs) synthesized through electrospinning technology are endowed with excellent mechanical strength and satisfactory electrical conductivity, which are regarded as an ideal matrix for composite materials. Hitherto, Mo-based materials incorporated with CNFs through electrospinning technology have arisen intensive attraction in SCs. The electrospinning strategy can realize evenly dispersed Mo-based materials in CNFs. The as-prepared Mo-based nanocomposite fibers with good flexibility and brilliant chemical properties can validly avoid the self-aggregation and enhance the electrochemical performance. In this review, the basic process and principle of the electrospinning technique, strategies to prepare CNFs with special structure, and various Mo-based nanocomposite fibers are introduced. In addition, the application of the Mo-based nanocomposite fibers in SCs, as well as the current situation and challenges of Mo-based nanocomposite fibers are also summarized.
This work developed a cost-effective and environmentally benign method for preparing high electrical conductivity carbon nanofibers (CNFs) from coal extraction residuals. The electrical conductivity of the CNFs prepared with PAN and 10.00 wt%, 30.00 wt%, and 50.00 wt% residual extracted tar (RET) increases by 70.89%, 164.31%, and 193.22% in comparison with conventional pure PAN-based CNF at the carbonization temperature of 1000 °C. The results of electrochemical impedance spectroscopy have shown that the total resistance for 50.00 wt% and 30.00 wt% RET-based CNFs prepared at the reaction temperature of 1000 °C was 0.61 Ω and 0.73 Ω, respectively, which is lower than that of coal extracted tar (CET)-based CNF and PAN-based CNFs. Raman analysis indicates that the 50.00 wt% RET-based CNF shows the lowest relative intensity of −0.953 and the highest degree of the ordered carbon structure. According to SEM results, fewer defects were observed in the carbon structure of RET-based CNFs. The cross-linking structure in 50.00 wt% RET can contribute to the improvement of the electrical conductivity of CNFs, which is consistent with the observation of Raman results. The GC-MS analysis results reveal that the aromatic and phenolic concentration in RET is 37.91% and 176.69% higher compared with those in CET. Both aromatic and phenolic concentrations in CNF precursor favor the formation of CNFs with fewer defects and thus lead to a higher electrical conductivity in CNF. The GC-MS results present consistency with those of Raman, SEM, and electrochemical performance measurements.
Here, we present the synthesis of novel poly(2,2′:5′,2″-terthiophene) derivatives containing oxyethylene pendant groups for the fabrication of high performance flexible redox-active electrode materials. The poly(3′,4′-bis(2-methoxyethoxy)-2,2′:5′,2″-terthiophene) (PSEDEN1), poly(3′,4′-bis(2-(2-methoxyethoxy)ethoxy)-2,2′:5′,2″-terthiophene) (PSEDEN2) and poly(3′,4′-bis(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)-2,2′:5′,2″-terthiophene) (PSEDEN3) have been electrochemically polymerized on flexible stainless steel substrates without any binder and directly employed as redox-active materials. The effect of pendant group chain length on morphological characteristics of conducting polymer films have been systematically evaluated and correlated to the charge storage properties of redox-active electrode materials. Capacitive performance tests reveal that PSEDEN1, PSEDEN2 and PSEDEN3 could reach up to specific capacitances of 135 F g⁻¹, 212.8 F g⁻¹ and 403.3 F g⁻¹, respectively, at constant current density of 2.5 mA cm⁻² in the potential range of 0.4 – 1.8 V with good rate capability performances. In addition, symmetrical flexible solid-state supercapacitor devices based on polymer gel electrolyte have also been assembled using PSEDEN1, PSEDEN2 and PSEDEN3 coated flexible stainless steel substrates and tested by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy techniques in detail. Fabricated devices (Cell 1, Cell 2 and Cell 3) have delivered maximum specific capacitances of Cspec= 29.3 F g⁻¹, 92.1 F g⁻¹ and 162.4 F g⁻¹, energy densities of SE= 6.35 W h kg⁻¹, 22.9 W h kg⁻¹ and 41.1 W h kg⁻¹ and power densities of SP= 929 W kg⁻¹, 937.7 W kg⁻¹ and 986.4 W kg⁻¹ at a current density of 2.5 mA cm⁻² in two-electrode cell configuration. Furthermore, flexible supercapacitor devices have achieved high cycle life performances with good capacitance retention values of 80.2%, 84.7% and 91.4% over 10 000 consecutive galvanic charge/discharge cycles at 2.5 mA cm⁻² constant current density from 0.4 V to 1.8 V. Similarly, excellent mechanical stabilities have also been observed with 3.4%, 4.66% and 1.97% capacitance losses under various bending conditions from 0° to 170° for all flexible supercapacitor devices. These results confirm that PSEDEN1, PSEDEN2 and PSEDEN3 redox-active materials with gratifying capacitive performances and excellent flexibilities have a great potential for utilization in innovative flexible or wearable energy storage solutions.
Electrospinning is an efficient and versatile technology to prepare continuous nanofibers. Carbon nanofibers prepared from electrospun nanofibers have a large surface area, high porosity and large liquid permeability, and good electrical conductivity; as a result, they have attracted growing attention as electrode materials for supercapacitor application. In this chapter, the progress made in carbon nanofiber-based electrodes and their electrochemical performances are reviewed. The selection of precursor materials, control of fiber morphology and pore structure engineering involved in making high-performance electrode materials will be summarized. Carbon composite nanofiber electrodes containing heteroatoms, transition metal compounds, or conducting polymers are discussed. Attention will particularly be paid toward the relationship between electrochemical performances and fiber porous structure and composition.
A simple ion exchange reaction of sodium lignosulfonate (SLS) and 1-allyl-3-methyl imidazolium chloride ([Amim]Cl) produced a new polymeric ionic liquid [Amim]LS and NaCl, and the mixture was successfully used as a precursor to prepare a nitrogen-doped porous carbon material via direct carbonization without any additional activation agent or template. It was believed that the in situ produced NaCl during the precursor synthesis process acted as the self-template and in self-activation. The introduction of imidazolium ionic liquid into the precursor raised the nitrogen content of the obtained carbon material up to 4.68% for a high yield of [Amim]LS-700 carbon material up to 34.6%. The effect of carbonization temperature on the structures and electrochemical properties of the prepared carbon were also studied systematically. It was found that the carbon material exhibits a superior gravimetric capacitance up to 230 F g⁻¹ (0.1 A g⁻¹) at the carbonization temperature of 700 °C, a good energy density of 7.99 W h kg⁻¹ at the power density of 25 W Kg⁻¹, and an excellent cycling stability of 90.3% after 20 000 cycles. This work provides a new path for the value-added utilization of biomass coupled with the field of electrochemical energy storage.
Carbon nanofibers from electrospun polymer nanofibers have received considerable attention. However, most of the carbon nanofibers with a surface area above 1000 m²/g were reported to have a supercapacitor electrode capacitance far below 350 F g⁻¹. Herein, we report a novel carbon nanofibrous material that has a supercapacitor electrode capacitance as high as 394 F g⁻¹ (1.0 A g⁻¹). We used a polymer blend of polyacrylonitrile (PAN) and novolac (NOC) as materials, to electrospin them into precursor nanofibers and subsequently carbonize the nanofibers into carbon nanofibers. The carbon nanofibers prepared had a specific surface area as high as 1468 m² g⁻¹ with a meso-micro pores (average pore size 2.2 nm) predominated porous structure. The carbon nanofiber electrodes after 10,000 cycles of charging and discharging at 1.0 A g⁻¹ maintained the capacitance almost unchanged. At the optimal condition, the supercapacitor device made of the electrodes had an energy density as high as 13.6 Wh∙kg⁻¹ (at 0.5 kW kg⁻¹). The high capacitance value comes from the carbon nanofibers with a large surface area and a unique porous structure. The high inter-fiber interconnection contributes to high capacitance. This super-high surface area carbon may be useful for the development of high-performance supercapacitors and other energy devices.
The development of low-cost, high-purity and high-performance porous carbon is of great significance for promoting the commercial application of supercapacitors. In this paper, porous carbon spheres (PCSs) with excellent electrochemical performance were obtained by carbonization and activation of starch gel spheres as precursor which is prepared by microemulsion process. The obtained PCSs exhibit both microporous and mesoporous structure, showing a large specific surface area of 1117.0 m ² g[Formula: see text] and exhibiting a high specific capacitance of 221.3 F g[Formula: see text]at a current density of 0.5 A g[Formula: see text] in aqueous electrolyte (and still displays capacity of 146.0 F g[Formula: see text] in ion liquid electrolyte). The PCSs//PCSs symmetric supercapacitor (SSC) based on aqueous electrolyte exhibits an energy density of 10.9 Wh kg[Formula: see text] at a power density of 300.0 W kg[Formula: see text], whereas that based on ion liquid electrolyte achieves a high energy density of 29.0 Wh kg[Formula: see text] at 650.0 W kg[Formula: see text]. The study provides a new idea to develop low-cost, high-purity and high-performance porous carbon materials for supercapacitors.
Blends of polyacrylonitrile (PAN) with three different sacrificial polymers: poly (acrylic acid) (PAA), poly (methyl methacrylate) (PMMA), and poly (styrene-coco-acrylonitrile) (SAN), were gel spun, oriented through the drawing process, stabilized and carbonized to obtain porous carbon fibers. Carbon fibers with an average pore diameter of 15 nm, 31 nm, 37 nm and 115 nm have been obtained from PAN-PAA (90/10), PAN-PMMA (90/10), PAN-SAN (90/10) and PAN-SAN (80/20) precursor fibers, respectively. The variation in pore size caused by the differences in compatibility between PAN and the sacrificial polymer was evaluated experimentally through blend rheology and theoretically using interaction parameter values. Despite their porosity, carbon fibers from PAN-PAA (90/10) and PAN-PMMA (90/10) exhibited tensile strength (∼1.6 GPa) comparable to that of the non-porous PAN based carbon fibers, processed under similar conditions. Specific tensile modulus of the porous carbon fibers was 15–40% higher than that for the PAN based carbon fibers, and the electrical conductivity was as high as 74 kS/m due to high graphitic ordering. Porous channels presented in this study were obtained by combining phase separation in the nano/micro scale range, with pore orientation and elongation achieved through gel spinning.
A flexible 3D hierarchical porous carbon membrane was simply fabricated for supercapacitor electrode by using polyacrylonitrile (PAN) and polyvinylidene fluoride (PVDF) as raw material and polyvinyl pyrrolidone (PVP) as additive via nonsolvent induced phase separation (NIPS) and carbonization. Experimental results show that the as-prepared carbon membranes display typical spongy skeleton structure and excellent flexibility. The specific surface area, micropore, mesopore, and total pore volume of the carbon membranes are increased with the increase of PVDF content. The prepared carbon membranes show large specific surface area (491 m² g⁻¹) and 3D hierarchical porous structure. As free-standing electrode for supercapacitors, the carbon membranes exhibit a high specific capacitance of 265 F g⁻¹ in three-electrode system and 212 F g⁻¹ in two-electrode system at 0.05 A g⁻¹ in 6 M KOH aqueous electrolyte. Such outstanding capacitive performance is due to the hierarchical porous structure and ameliorated surface chemical functional groups, offering a favorable pathway for ion penetration, considerable surface for accumulation of electrolyte ions and improving the surface accessibility for electrolyte ions. It is believed that the simple and effective approach to hierarchical porous carbon membranes have good application prospect in production of freestanding electrode of supercapacitors.
In the present study, electrically conducting carbon nanofiber (CNF) mats were produced by incorporating tetraethoxy orthosilicate (TEOS) into polyacrylonitrile (PAN) via electrospinning. A simple thermal treatment was applied to the electrospun nanofibers to create ultramicropores that could accommodate a large number of ions were formed on the surface of the CNFs, removing the need for a time-consuming activation step. The Si/CNF composites showed high capacitance and energy/power density values due to the formation of ultramicropores and the introduction of heteroatoms.
The study compares the structural and electrochemical properties of 12 porous carbons based on phenolic resins, using both aqueous (H2SO4) and aprotic ((C2H5)4NBF4 in acetonitrile) electrolytes. It appears that they fit into the general pattern observed for other carbons. The present carbons have micropore volumes varying between 0.29 and 0.66 cm3 g−1 and average pore widths Lo between 0.62 and 1.23 nm. Five samples are exclusively microporous, whereas seven also display a relatively important mesoporosity. This allows a direct comparison between pairs of carbons with similar micropore systems, with and without mesopores, in order to assess the role of mesoporosity in the electrochemical properties. It appears that mesopores have only a limited influence on the decrease in capacitance at high current density as opposed to earlier assumptions.
The electrochemical storage of energy in various carbon materials (activated carbons, aerogels, xerogels, nanostructures) used as capacitor electrodes is considered. Different types of capacitors with a pure electrostatic attraction and/or pseudocapacitance effects are presented. Their performance in various electrolytes is studied taking into account the different range of operating voltage (1 V for aqueous and 3 V for aprotic solutions). Trials are undertaken for estimating the role of micro and mesopores during charging the electrical double layer in both kinds of electrolytic solutions for which the electrical conductivity and the size of solvated ions are different. The effect of pseudocapacitance for maximising the total capacitance is especially documented. Carbons chemically modified by a strong oxidation treatment represent a very well defined region of pseudocapacitance properties due to the Faradaic redox reactions of their rich surface functionality. Conducting polymers (polyaniline, polypyrrole, polythiophene derivatives) and oxidised metallic particles (Ru, Mn, Co,…) deposited on the carbons also participate in the enhancement of the final capacity through fast faradaic pseudocapacitance effects. Evaluation of capacitor performance by different techniques, e.g. voltammetry, impedance spectroscopy, charge/discharge characteristics is also discussed.
Carbon supercapacitors, which are energy storage devices that use ion adsorption on the surface of highly porous materials to store charge, have numerous advantages over other power-source technologies, but could realize further gains if their electrodes were properly optimized. Studying the effect of the pore size on capacitance could potentially improve performance by maximizing the electrode surface area accessible to electrolyte ions, but until recently, no studies had addressed the lower size limit of accessible pores. Using carbide-derived carbon, we generated pores with average sizes from 0.6 to 2.25 nanometer and studied double-layer capacitance in an organic electrolyte. The results challenge the long-held axiom that pores smaller than the size of solvated electrolyte ions are incapable of contributing to charge storage.
With increasing the concern to clean energy device, such as electric vehicle (EV), electric double layer capacitor (EDLC) is considered as an indispensable to recover the uneven load level required for practical operation in diverse applications when compared with other energy sources. The development of EDLCs has deep relation to the carbon materials with highly porous structure (>1000m2/g). Until now, contributions of carbon science to elucidating the relation between electrode and electrolyte have been enormous, and further achievement of future scientific studies on new forms of carbons, such as activated carbon, could afford even larger success in the development of EDLC. In this review, we depict the various parameters related to EDLC performance, on the basis of our research results. In particular, the size effect of the electrolyte ion, the morphological effects of active materials, are discussed.
Unsupervised clustering approachesModule-based approachesFinal remarksReferences
Thin film supercapacitors were fabricated using printable materials to make flexible devices on plastic. The active electrodes were made from sprayed networks of single-walled carbon nanotubes (SWCNTs) serving as both electrodes and charge collectors. Using a printable aqueous gel electrolyte as well as an organic liquid electrolyte, the performances of the devices show very high energy and power densities (6 W h/kg for both electrolytes and 23 and 70 kW/kg for aqueous gel electrolyte and organic electrolyte, respectively) which is comparable to performance in other SWCNT-based supercapacitor devices fabricated using different methods. The results underline the potential of printable thin film supercapacitors. The simplified architecture and the sole use of printable materials may lead to a new class of entirely printable charge storage devices allowing for full integration with the emerging field of printed electronics.
Design and synthesis of amphiphilic star-shaped polymers with complex architecture are always pursued by polymer chemists in past decades. Thanks to the development of living polymerization, combining the living radical polymerization with ionic polymerization, all kinds of amphiphilic star-shaped polymers are synthesized. In this paper, the classification and the recent studies in synthesis of amphiphilic star-shaped polymers were reviewed. Three routes of synthesis of amphilic star-shaped polymers by core-first, arm-first and assembly were briefly recommended and evaluated. These special architectural polymers may form abundant morphologies in selective solvent or in bulk and have potential applications in chemistry, physics and biology.
Novel ordered hierarchical mesoporous/microporous carbon (OHMMC) derived from mesoporous titanium-carbide/carbon composites was prepared for the first time by synthesizing ordered mesoporous nanocrystalline titanium-carbide/carbon composites, followed by chlorination of titanium carbides. The mesostructure and microstructure can be conveniently tuned by controlling the TiC contents of mesoporous TiC/C composite precursor, and chlorination temperature. By optimal condition, the OHMMC has a high surface area (1917 m2g−1), large pore volumes (1.24 cm3g−1), narrow mesopore-size distributions (centered at about 3 nm), and micropore size of 0.69 and 1.25 nm, and shows a great potential as electrode for supercapacitor applications: it exhibits a high capacitance of 146 Fg−1 in noaqueous electrolyte and excellent rate capability. The ordered mesoporous channel pores are favorable for retention and immersion of the electrolyte, providing a more favorable path for electrolyte penetration and transportation to achieve promising rate capability performance. Meanwhile, the micropores drilled on the mesopore-walls can increase the specific surface area to provide more sites for charge storage.
Improvements in the energy density of electric double-layer capacitors (EDLCs) can in particular be gained by enhancing their capacitance. Recent findings suggest that the specific capacitance can be increased by matching the sizes of pores and desolvated ions. However, on such matching, we evidenced that charge storage saturation can occur in organic electrolyte before reaching the maximum voltage, e.g. 2.7 V, due to the insufficiently developed porosity. The experimental charge is larger than the calculated on account of the size of rigid cations, because of the intercalation-like behaviour and/or distortion of ions. The experimental and calculated values are less coincident for the higher sweep rates, which reveals that the optimal average pore size should depend on the current load, tending to shift to higher values in the normal usage conditions of supercapacitors.
The relationship between electric double-layer properties in an organic electrolytic solution and a concentration of surface acidic functional groups (surface acidity) of a phenolic resin-based activated carbon fiber (ACF) was characterized in a system of ACF/electrolytic solution/ACF The lower surface acidity of ACF resulted in the lower apparent leakage current of the electric double layer. The capacitance and the dc resistance of the layer were almost independent of the surface acidity. Further heat treatment of ACF in nitrogen atmosphere decreased the surface acidity of ACF. Types of C-O bonds in surface acidic functional groups were identified as carboxy and ester groups for ACF as-prepared and as phenolic hydroxy and quinone groups for ACF heat treated. The ACF obtained from the phenolic resin-based fibers showed an extremely low surface acidity in comparison with other kinds of ACF. The polarizable electrodes of the phenolic resin-based ACF resulted in electric double-layer capacitors with high capacitance and low leakage current.
A three-dimensional (3D) hierarchical porous carbon structure was prepared with possible variations in porosity at three levels of length scales. The carbon structure was template-synthesized from a core–shell silica sphere assembly. The as-synthesized carbon featured a semi-ordered porous structure with hollow macro-cores (330 nm) surrounded by a mesoporous shell containing uniform pores of 3.9 nm and distinct interstitial space between the core–shell domains. The mesoporous shell thickness was stepwise increased from 0, 25, 50 to 100 nm while keeping an identical core size to create a family of hierarchical porous structures for a systematic investigation of electrochemical capacitance and ionic transport. The shell thickness affected the overall porosity and relative porosities of the shell, core, and interstitial regions. A thicker mesoporous shell possessed a higher surface area which led to a proportional increase in electrochemical capacitance which can be fully realised at low scan rates. For the carbon structure with the maximum shell thickness of 100 nm, electrochemical capacitance per unit area and power density declined at high scan rates and high currents when ionic transport through long mesopores became limiting. The power density of the better as-synthesized porous carbon was up to 11.7 kW kg−1 when the corresponding energy density was 5.9 W h kg−1.
A novel doped activated carbon has been prepared from H2SO4-doped polyaniline which is prepared by the oxypolymerization of aniline. The morphology, surface chemical composition and surface area of the carbon have been investigated by scanning electron microscope, X-ray photoelectron spectroscopy and Brunaner–Emmett–Teller measurement, respectively. Electrochemical properties of the doped activated carbon have been studied by cyclic voltammograms, galvanostatic charge/discharge, and electrochemical impedance spectroscopy measurements in 6moll−1 KOH. The specific capacitance of the carbon is as high as 235Fg−1, the specific capacitance hardly decreases at a high current density 11Ag−1 after 10,000 cycles, which indicates that the carbon possesses excellent cycle durability and may be a promising candidate for supercapacitors.
Various kinds of activated carbon/activated carbon fibers were used in the evaluation of electrical double layer capacitors using the method of image analysis. The appropriate hydrated ion structures in an aqueous system of H2SO4 /H2O and an organic system of LiClO4/Polypropylene carbonate were calculated using the software Cerius(2) (ver. 3.8). The capacitance obtained varied with the electrolyte used, even though the capacitor material remained the same. The relationship between the pore size and the electrolyte ion diameter is discussed. (C) 2001 The Electrochemical Society.
For amorphous ruthenium, the current-voltage characteristics of cyclic voltammetric (CV) curves depended strongly on the voltage scan rate. At high voltage scan rates, asymmetrical reduction and oxidation current behavior was obtained. The specific capacitance decreased with increasing voltage scan rate. The composite electrode was made by mixing ruthenium oxide powders and activated carbon black. The CV curve symmetry improved significantly at high voltage scan rates using composite electrodes, and the specific capacitance was less sensitive to the voltage scan rate. An electrochemical capacitor made with ruthenium oxide-carbon composite electrodes demonstrated current densities as high as 1.57 A/cm(2).
A simple and efficient method to tailor the pore size of wormholelike mesoporous carbons (WMCs) has been developed by adding a proper amount of hydrofluoric acid (HF) during the sol-gel process of tetraethyl orthosilicate (TEOS). It was found that the pore size increased obviously from 3.1 to 8.5 nm when increasing HF/TEOS molar ratio from 0 to 1/7. Brunauer–Emmett–Teller surface area decreased accordingly. In addition, mesopore volume of WMCs basically kept unvaried due to their identical silica template amount.
Graphene, graphene–ZnO and graphene–SnO2 films were successfully synthesized and used as electrode materials for electrochemical supercapacitors, respectively. The screen-printing approach was employed to fabricate graphene film on graphite substrate while the ZnO and SnO2 were deposited on graphene films by ultrasonic spray pyrolysis. The electrochemical performances of these electrodes were comparatively analyzed through electrochemical impedance spectrometry, cyclic voltammetry and chronopotentiometry tests. The results showed that the incorporation of ZnO or SnO2 improved the capacitive performance of graphene electrode. Graphene–ZnO composite electrode exhibited higher capacitance value (61.7F/g) and maximum power density (4.8kW/kg) as compared with graphene–SnO2 and pure graphene electrodes.
Various porous carbons were prepared by CO2 activation of ordered mesoporous carbons and used as electrode materials for supercapacitor. The structures were characterized by using X-ray diffraction, transmission electron microscopy and nitrogen sorption at 77K. The effects of CO2 treatment on their pore structures were discussed. Compared to the pristine mesoporous carbons, the samples subjected to CO2 treatment exhibited remarkable improvement in textural properties. The electrochemical measurement in 6M KOH electrolyte showed that CO2 activation leads to better capacitive performances. The carbon CS15A6, which was obtained after CO2 treatment for 6h at 950°C using CMK-3 as the precursor, showed the best electrochemical behavior with a specific gravimetric capacitance of 223F/g and volumetric capacitance of 54F/cm3 at a scan rate of 2mV/s and 73% retained ratio at 50mV/s. The good capacitive behavior of CS15A6 may be attributed to the hierarchical pore structure (abundant micropores and interconnected mesopores with the size of 3–4nm), high surface area (2749m2/g), large pore volume (2.09cm3/g), as well as well-balanced microporosity and mesoporosity.
The electrochemical capacitance of porous carbon materials including activated carbon, carbon nanotubes, and carbon gels were investigated. Due to their different porous structures, these carbons showed different capacitive behaviors in aqueous solutions and ionic liquids. It was found that carbon nanotubes, having the largest micropore volume, and the carbon gels with 3D macroporous framework presented the opposite results in charge capacity in the two media. The experimental data showed that microporous materials presented the higher capacitance in aqueous solutions, while macropores were more favorable for improving power and energy properties in ionic liquids owing to the higher operable voltage of the ionic liquids. This may imply that the capacitive performance of a porous material depends more on its matching degree to the applied electrolytes than on its overall pore volume. Carbon materials with ample macropores could be more suitable to be used in ionic liquids to fully exert the energy output for a capacitor. An electrochemical capacitor based on 3D macroporous carbon gels in ionic liquids has been demonstrated to show a specific energy of 58 W h kg−1, comparable to a commercial battery.
Mesoporous carbon spheres with hierarchical foam-like pore structures have been synthesized by a dual-templating strategy using phenolic resol as a carbon source, Pluronic F127 and spherical silica mesocellular foams (Si-MCFs) as the soft and hard template, respectively. The results show that the morphology and mesostructure of the silica template are faithfully replicated. The obtained mesoporous carbon material with spherical diameter size of ca. 3–5 μm exhibits hierarchical pore sizes (from ca. 3.5 to 60 nm), high specific surface area (1320 m2/g) and large pore volume (3.5 cm3/g). The carbon surface contains plenty of oxygen-containing groups, resulting in hydrophilic property for an electrode material. In addition, Pluronic F127 plays an important role in the synthesis for maintaining the foam-like mesostructure of the silica templates and faithful replication of the spherical morphology. The electrochemical measurements show that the hierarchically mesoporous carbon spheres as an electrochemical double-layer capacitor (EDLC) electrode present a long cyclic life, excellent rate capability, and high specific capacitance as ca. 208 F/g at 0.5 A/g in (2.0 M) H2SO4 aqueous solution. Its specific capacitance can still remain ca. 146 F/g at a high loading current density of 30 A/g with the retention of ca. 70%. Furthermore, this material also exhibits excellent capacitive performance in (C2H5)4NBF4/propylene carbonate electrolyte, and its specific capacitance is 97 F/g at loading current density of 0.5 A/g.
Supercapacitors (also known as 'ultracapacitors') offer a promising alternative approach to meeting the increasing power demands of energy-storage systems in general, and of portable (digital) electronic devices in particular. Supercapacitors are able to store and deliver energy at relatively high rates (beyond those accessible with batteries) because the mechanism of energy storage is simple charge-separation (as in conventional capacitors). The vast increases in capacitance achieved by supercapacitors are due to the combination of: (i) an extremely small distance that separates the opposite charges, as defined by the electric double-layer; (ii) highly porous electrodes that embody very high surface-area. A variety of porous forms of carbon are currently preferred as the electrode materials because they have exceptionally high surface areas, relatively high electronic conductivity, and acceptable cost. The power and energy-storage capabilities of these devices are closely linked to the physical and chemical characteristics of the carbon electrodes. For example, increases in specific surface-area, obtained through activation of the carbon, generally lead to increased capacitance. Since only the electrolyte-wetted surface-area contributes to capacitance, the carbon processing is required to generate predominantly 'open' pores that are connected to the bulk pore network. While the supercapacitors available today perform well, it is generally agreed that there is considerable scope for improvement (e.g., improved performance at higher frequencies). Thus it is likely that carbon will continue to play a principal role in supercapacitor technology, mainly through further optimization of porosity, surface treatments to promote wettability, and reduced inter-particle contact resistance. © 2006 Published by Elsevier B.V.
A simple two-stage technique for producing turbostratic carbon nanotubes via the co-electrospinning of two polymer solutions is described. These strong carbon nanotubes (see Figure) can be produced in lengths of the order of 10 cm while still maintaining submicrometer inner and outer diameters. They can be used in numerous applications, such as in drug delivery, hydrogen storage, and microfluidics.
Elektrochemische Kondensatoren: Ein hierarchisches poröses Material auf Graphitbasis enthält makroporöse ionengepufferte Mikroreservoirs, Kanäle für den Ionentransport und lokalisierte Graphitstrukturen (siehe Bilder des Gerüsts (oben) und eines Kohlenstoffplättchens). Das neue Material löst Probleme der Elektrodenkinetik, die anderen elektrochemischen Kondensatoren anhaften, und ist daher hervorragend für die schnelle Energiespeicherung geeignet.
Poly(acrylonitrile) solutions in dimethylformamide were electrospun to be webs consisting of 300 nm ultrafine fibers. The webs were oxidatively stabilized and activated by steam resulting in activated carbon nanofibers (ACNFs). The specific surface area of the ACNF activated at 700 ° C was the highest but mesopore volume fraction of that was lowest. On the other hand, the ACNFs activated at 800 ° C showed opposite trends to those activated at 700 ° C . The high specific surface area, mainly due to the micropores, introduced maximum specific capacitance at low current density (173 F/g at 10 mA/g). The elevated volume fraction of mesopores gave maximum specific capacitance at high current density (120 F/g at 1000 mA/g). The behavior is explained on the basis of ion mobility in the pores. © 2003 American Institute of Physics.
Polyaniline/multi-walled carbon nanotubes composites were synthesized by an in situ chemical oxidative polymerization method and were the new electrode materials used for supercapacitor. The composites were characterized physically by transmission electron microscope and X-ray diffraction. The electrochemical capacitance performance of the composites in neutral solution (NaNO3) was investigated by cyclic voltammetry, galvanostatic charge–discharge tests and ac impedance spectroscopy with a three-electrode system. The polyaniline/multi-walled carbon nanotubes composites electrodes showed much higher specific capacitance (328 F g−1), better power characteristics and were more promising for application in capacitor than pure polyaniline electrodes. This may be attributed to the introduction of multi-walled carbon nanotubes. The improvement mechanisms of multi-walled carbon nanotubes in the composites electrode were also discussed in detail.
Porous doped carbons were synthesized by casting technique using zeolite 13X as the template through a polymerization reaction between ethylenediamine and carbon tetrachloride. The nitrogen contents and pore structures were further tailored by carbon dioxide and potassium hydroxide activations. These parameters played important roles in the electrochemical capacitors. The nitrogen- and oxygen-containing functional groups can make pseudocapacitance contribution to the overall capacitance, but face the disadvantage of blocking the electrolyte ions into pores. The investigation of relationship between the capacitance and the surface area or volume of the micropores indicated that high capacitance can be obtained for the carbon with large surface area and volume of micropores. Moreover, the mesopores in the carbons can be favor for smooth ion transfer. The porous doped carbon material with large specific surface area up to 2970 m2 g−1 and volume of the micropores up to 1.04 cm3 g−1 was achieved after the KOH activation, which exhibits the optimized electrochemical behavior with the gravimetric capacitances of 259 F g−1 in 6 M potassium hydroxide electrolyte and 176 F g−1 in acetonitrile solution containing 1.5 M tetraethylammonium tetrafluoroborate electrolyte at the current density of 0.25 A g−1.
The porous structure and electrochemical double layer capacitance of porous carbons prepared from rice husks by using alkali hydroxide as activating agents were investigated. Three samples of carbons prepared by NaOH-activation, three samples prepared by KOH-activation and two samples of commercial carbons have been studied. The porosity of the carbons was characterized by nitrogen adsorption isotherms at 77 K and electrochemical constant current cycling method was used to measure the double layer capacitance. The specific capacitance of the carbons is not linearly proportional to the surface area. Additionally, the double layer capacitance strongly depends on the pore structure and the functional groups. A specific capacitance larger than 200 F g−1 was achieved by using the porous carbon prepared with NaOH (activation temperature: 750 °C; activation time: 30 min). All the carbons prepared with rice husk in this study have larger double layer capacitance (125–210 F g−1) than the commercial grade carbons (78–100 F g−1).
The multi-walled carbon nanotube (CNT)-embedded activated carbon nanofibers (ACNF/CNT) and activated carbon nanofibers (ACNF) were prepared by stabilizing and activating the non-woven web of polyacrilonitrile (PAN) or PAN/CNT prepared by electrospinning. Both ACNF and ACNF/CNT were partially aligned along the winding direction of the drum winder. The average diameter of ACNF was 330 nm, while that of ACNF/CNT was lowered to 230 nm with rough surface. This was attributed to the CNT-added polymer solution in the electrospinning process providing finer fibers by increasing the electrical conductivity compared with the CNT-free one. The specific surface area and electrical conductivity of ACNF were 984 m2/g and 0.42 S/cm, respectively, while those of ACNF/CNT were 1170 m2/g and 0.98 S/cm, respectively. PPy was coated on the electrospun ACNF/CNT (PPy/ACNF/CNT) by in situ chemical polymerization in order to improve the electrochemical performance. The capacitances of the ACNF and PPy/ACNF electrodes were 141 and 261 F/g at 1 mA/cm2, respectively, whereas that of PPy/ACNF/CNT was 333 F/g. This improvement in capacitance was attributed to the following: (i) the preparation of aligned nano-sized ACNF/CNT by electrospinning and the addition of CNT and (ii) the formation of a good charge-transfer complex by the PPy coating on the surface of the aligned nano-sized ACNF/CNT. The former leads to a good morphology and superior properties, such as a higher surface area, the formation of mesopores and an increase in electrical conductivity. The latter offers a refined three-dimensional network due to the highly porous structure between ACNF/CNT and PPy.
Porous carbon nanofiber paper has been obtained by one-step carbonization/activation of PAN-based nanofiber paper at temperatures from 700 to 1000 °C in CO2 atmosphere. The paper was used as supercapacitor electrode without any binder or percolator. At low temperature, e.g., ⩽900 °C, nitrogen enriched carbons with a poorly developed specific surface area (SBET ⩽ 400 m2/g) are obtained. In aqueous electrolytes, these carbons withstand high current loads without a noticeable decrease of capacitance, and the normalized capacitance reaches 67 μF/cm2. At 10 s time constant, the values of energy and power densities are 3–4 times higher than for activated carbons (AC) presenting higher specific surface area. By carbonization/activation at 1000 °C, subnanometer pores are developed and SBET = 705 m2/g. Despite moderate BET specific surface area, the capacitance reaches values higher than 100 F/g in organic electrolyte. At high power densities, the nanofiber paper obtained at 1000 °C outperforms the energy density retention of ACs in organic electrolyte. The high power capability of the carbon nanofiber papers in the two kinds of electrolytes is attributed both to the high intrinsic conductivity of the fibers and to the high diffusion rate of ions in the opened mesopores.
Hierarchically porous composite materials consisting of nanoflake-like nickel hydroxide and mesoporous carbon are synthesized by a facile chemical precipitation method. The effects of microstructure and morphology of the carbon support on the electrochemical properties of the composite are also investigated. Structural characterizations have revealed that nanometer-sized nickel hydroxide nanoflakes can grow on the surface of mesoporous carbon supports. The mesoporous carbon-based composites shows better structure with interlaced nanoflakes and higher specific capacitance than activated carbon-based composite. The composite material with mesoporous carbon morphology of large particle size and long channel lengths possesses the highest specific capacitance of 2570 F/g, suggesting its potential applications as the electrode materials for electrochemical capacitors. The overall improved electrochemical behavior can be attributed to the unique structure design in nickel hydroxide/mesoporous carbon composite in terms of its nanostructure, large specific surface area and good electrical conductance.
An ordered mesoporous carbon with a high surface area of 2390 m2/g and a large pore size of 6.7 nm was synthesized through an organic–inorganic-surfactant tri-constituent co-assembly method which used resols as the carbon precursor, silicate oligomers as the inorganic precursor and triblock copolymer as the soft template. The electrochemical properties of this carbon were evaluated as an electrode material for electrochemical double layer capacitor and lithium-ion battery. It shows rectangular-shaped cyclic voltammetry curves over a wide range of scan rates even up to 200 mV/s between 0 and 3 V, with a large capacitance of 112 F/g in nonaqueous electrolyte. As a negative electrode material for lithium-ion battery, it delivers a reversible specific capacity as high as 1048 mAh/g and a good cycling ability with capacity retention of 500 mAh/g over 50 cycles.
The worldwide market for capacitors was approximately US$ 12.3 billion in 1993, of which production within Japan accounted for approximately 50% and the combined domestic and overseas production of Japanese manufacturers accounted for approximately 70%. The worldwide capacitor market continues to grow by approximately 20% per year as the demand for ICs and LSIs is growing. In conjunction with this special issue on capacitors, this paper presents a corporate perspective on current trends in the capacitor market: capacitor principles; capacitor materials; capacitor types and major characteristics; recent technical trends in capacitors and the future market outlook, and technical problems in the hope of facilitating the understanding of ideas and concepts presented in other papers in this issue.
Rubber composite sheets filled with 5 wt.% and 30 wt.% of highly aligned carbon nanotubes (CNTs) were fabricated through conventional rubber technology. The alignment of CNTs was possibly derived from dragged shear force during the optimized milling process. The selective alignment of CNTs led to enhancements in the elastic modulus, thermal conductivity, electrical conductivity, and electromagnetic shielding property, compared to neat rubber sheet. (c) 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
High surface area nanoporous carbon has been prepared by thermo-chemical etching of titanium carbide TiC in chlorine in the temperature range 200–1200 °C. Structural analysis showed that this carbide-derived carbon (CDC) was highly disordered at all synthesis temperatures. Higher temperature resulted in increasing ordering and formation of bent graphene sheets or thin graphitic ribbons. Soft X-ray absorption near-edge structure spectroscopy demonstrated that CDC consisted mostly of sp2 bonded carbon. Small-angle X-ray scattering and argon sorption measurements showed that the uniform carbon-carbon distance in cubic TiC resulted in the formation of small pores with a narrow size distribution at low synthesis temperatures; synthesis temperatures above 800 °C resulted in larger pores. CDC produced at 600–800 °C show great potential for energy-related applications. Hydrogen sorption experiments at −195.8 °C and atmospheric pressure showed a maximum gravimetric capacity of ∼330 cm3/g (3.0 wt.%). Methane sorption at 25 °C demonstrated a maximum capacity above 46 cm3/g (45 vol/vol or 3.1 wt.%) at atmospheric pressure. When tested as electrodes for supercapacitors with an organic electrolyte, the hydrogen-treated CDC showed specific capacitance up to 130 F/g with no degradation after 10 000 cycles.
Nanoporous carbons were prepared by using colloidal crystal as a template. Nitrogen adsorption/desorption isotherms and transmission electron microscope images revealed that the porous carbons exhibit hierarchical porous structures with meso/macropores and micropores. Electric double layer capacitor performance of the porous carbons was investigated in an organic electrolyte of 1 M LiClO4 in propylene carbonate and dimethoxy ethane. The hierarchical porous carbons exhibited large specific double layer capacitance of ca. 120 F g−1 due to their large surface areas. In addition, the large capacitance was still obtained at a large current density up to 10 A g−1, which satisfies demands from the high power application such as hybrid electric vehicles. Capacitance analysis of the hierarchical porous structures revealed the contribution of meso/macropores and micropore to the electric double layer capacitance to be 8.4 and 8.1 μF cm−2, respectively. The results indicated electric double layer is formed even when solvated ions are larger than pore diameters.
Under a lower carbonization temperature and with a mesophase pitch solution as the carbon precursor, ordered mesoporous carbon thick films with 35-nm pore size have been synthesized using SiO2 spheres as the template. The pore size of the mesoporous carbon thus fabricated was the smallest one ever reported using silica templates. XRD and Raman spectroscopy suggest a microstructure of carbon with low crystallinity. SEM and TEM patterns show a discernible morphology of an ordered hexagonal close-packing of the mesopores interconnected via holes of 6 nm in diameter. A fair BET surface area of 502 m2/g and a total pore volume of 0.861 cm3/g, along with the characteristic pore structure and hysteresis loop, are identified.
A series of hierarchical porous carbons (HPCs) were prepared by a combination of self-assembly and chemical activation. Pore-structure analysis shows that micropores can be generated within the mesopore wall of mesoporous carbon in a controllable manner during activation. As evidenced by cyclic voltammetry, galvanostatic charge/discharge cyclings and frequency response measurements, HPCs show superior capacitive performances to hard-templated ordered mesoporous carbons, which can be attributed to the generated pore surfaces that play most important role in the formation of double-layer capacitance and to their unique hierarchical porous structure that favors the fast diffusion of electrolyte ions into the pores. Of special interest is the fact that HPCs maintains 180 F/g at high-frequency of 1 Hz.
Liu’s polytomous ordering theory algorithm can be used for any testing with homogeneous or heterogeneous polytomous response. It is more useful than other well known polytomous ordering theory. However, its threshold limit value is a fixed value, lacking of statistical meaning, In this paper, the authors provide an improved threshold limit value by using the empirical distribution critical value of all the values of the ordering indices between any two items. For comparing the performance of two ordering theory models, a calculus test with polytomous items of Chung Chou Institute of Technology is conducted. The experimental results show that the new method has the better performance. A computer program is developed for the proposed method.
Energy production and storage are both critical research domains where increasing demands for the improved performance of energy devices and the requirement for greener energy resources constitute immense research interest. Graphene has incurred intense interest since its freestanding form was isolated in 2004, and with the vast array of unique and highly desirable electrochemical properties it offers, comes the most promising prospects when implementation within areas of energy research is sought. We present a review of the current literature concerning the electrochemical application of graphene in energy storage/generation devices, starting with its use as a super-capacitor through to applications in batteries and fuel cells, depicting graphene’s utilisation in this technologically important field.
Given the recent withdrawal of daclizumab (DAC), the safety and efficacy of thymoglobulin (TMG) was tested as an alternative induction agent for steroid-free (SF) immunosuppression in pediatric kidney transplant recipients.
Thirteen pediatric renal transplant recipients meeting defined high-risk criteria at transplantation were offered TMG induction and SF immunosuppression with maintenance mycophenolate mofetil and tacrolimus between October 2008 and January 2010. Patients were closely monitored at baseline, 3, 6, 9, and 12 months posttransplant for protocol biopsy and clinical outcomes. Outcomes were compared with 13 consecutively transplanted low-risk patients receiving an established DAC-based SF protocol (Sarwal et al., WA, American Transplant Congress 2003).
There was a significant trend for overall decrease in the absolute lymphocyte counts in TMG group (F=5.86, mixed model group effect P=0.02), predominately at 3 months compared with DAC group (0.7±0.6 vs. 2.1±1.0, P=0.0004); however, lymphocyte count was recovered and was back to reference range by 6 months in TMG. There was trend toward more subclinical cytomegalovirus (15% vs. 0%) and BK viremia (17% vs. 0%) in the TMG group, with no differences in the incidence of subclinical Epstein Barr virus viremia (23% vs. 31%) or clinical viral disease. Mean graft function was excellent, and with a minimum follow-up of 6 months, there were no episodes of acute rejection.
TMG seems to be a safe alternative induction strategy in patients for SF immunosuppression in pediatric renal transplantation. Extended follow-up and greater enrollment are necessary to fully explore the impact of TMG dosing on viral replication posttransplantation.
In order to achieve high energy and power densities, we developed a high-voltage asymmetric electrochemical capacitor (EC) based on graphene as negative electrode and a MnO(2) nanowire/graphene composite (MGC) as positive electrode in a neutral aqueous Na(2)SO(4) solution as electrolyte. MGC was prepared by solution-phase assembly of graphene sheets and α-MnO(2) nanowires. Such aqueous electrolyte-based asymmetric ECs can be cycled reversibly in the high-voltage region of 0-2.0 V and exhibit a superior energy density of 30.4 Wh kg(-1), which is much higher than those of symmetric ECs based on graphene//graphene (2.8 Wh kg(-1)) and MGC//MGC (5.2 Wh kg(-1)). Moreover, they present a high power density (5000 W kg(-1) at 7.0 Wh kg(-1)) and acceptable cycling performance of ∼79% retention after 1000 cycles. These findings open up the possibility of graphene-based composites for applications in safe aqueous electrolyte-based high-voltage asymmetric ECs with high energy and power densities.
Liver transplantation is an effective treatment for patients with many kinds of liver diseases. However, an increased risk of de novo malignancy has been reported in liver transplant recipients; immunosuppressive drugs have generally been identified as the primary culprit. Interdigitating dendritic cell sarcoma (IDCS) is an exceedingly rare neoplasm arising from antigen-presenting cells of the immune system. In this study, we have reported a case of IDCS with bone marrow involvement occurring in a 61-year-old female liver transplant recipient at 2 years after the procedure. She was admitted to our center with fever, cough, and expectoration. Physical examination revealed firm and painless nodes in both cervical and axillary fossae. Routine examination revealed an abnormal white blood cell count and elevated serum lactate dehydrogenase. Computerized tomography of the chest, abdomen, and pelvis were negative. Viral infections were also excluded. To obtain a definite diagnosis, we performed an excisional lymph node biopsy and a bone marrow biopsy. Microscopically, the tumor was composed of spindle cells with pale to eosinophilic cytoplasm, ill-defined cell borders, and large pleomorphic nuclei with prominent nucleoli. Immunophenotypic analysis demonstrated positive staining for S-100, vimentin, CD163, and CD68. Follicular dendritic cell, lymphoid, epithelial, myoepithelial, and melanoma markers were negative. Histology revealed bone marrow involvement. Taken together, the above features were consistent with IDCS with bone marrow involvement. She responded to chemotherapy. This case demonstrates the importance of cancer prevention and early detection for liver transplant recipients.
Carbon nanotubes prepared from core-shell polymer particles are reported. As depicted in the Figure, polymethylmethacrylate (PMMA) core/polyacrylonitrile (PAN) shell microspheres are blended with a PMMA matrix, spun, and elongated. Then the shell is stabilized and finally carbonized to produce contaminant-free carbon nanotubes.
Composite films of chemically converted graphene (CCG) and polyaniline nanofibers (PANI-NFs) were prepared by vacuum filtration the mixed dispersions of both components. The composite film has a layered structure, and PANI-NFs are sandwiched between CCG layers. Furthermore, it is mechanically stable and has a high flexibility; thus, it can be bent into large angles or be shaped into various desired structures. The conductivity of the composite film containing 44% CCG (5.5 x 10(2) S m(-1)) is about 10 times that of a PANI-NF film. Supercapacitor devices based on this conductive flexible composite film showed large electrochemical capacitance (210 F g(-1)) at a discharge rate of 0.3 A g(-1). They also exhibited greatly improved electrochemical stability and rate performances.
The fabrication of a porous carbon in the form of a web consisting of linear nanofibers is achieved through the combination of fiber formation by electro-spinning two stable, immiscible polymer solutions, and thermal treatment at 1000°C in an inert atmosphere. These high-temperature-treated nanofiber webs can be utilized as efficient electromagnetic shielding materials due to their low density and expected high, selective thermal and electrical conductivities along the plane. The air stabilization of electrospun nanofibers, which involves complex chemical reactions, is accompanied by a color change from white to reddish brown. This carbon nanofiber are promising candidates for a wide range of applications in which web morphology and controlled pore structure are significantly required.
The study of charged solid–liquid interfaces, manifested as “double layers”, represents a problem of both practical and scientific importance. Double layers are present in all electrolyte solutions and have been traditionally studied using planar noble-metal electrodes and mercury drops. However, in the ionic channels in cells or the small-diameter pores of electrochemical double-layer capacitors (EDLCs),ions are in a very confined situation, which is different from that of a planar solid/electrolyte interface. By using nanoporous carbon with pores smaller than the size of an ion and a single associated solvent molecule, we show that the implicit assumption that double layers are governed only by ion/ electrode charge separation may be short-sighted. Other factor may play a more dominant role than previously thought, for example, increasing the confinement of the ions leads to an increase in the capacitance. Including the effect of partially desolvating ions in the current double-layer theory could lead to a better understanding of the behavior of ions in confined environments.
This paper presents a three-phase claw pole permanent magnet soft magnetic composite motor, which was designed to take advantage of specific properties of the material. Parameter calculations by the finite element magnetic field analysis and performance prediction by the equivalent circuit are discussed. To verify the theory, a prototype motor was constructed and operated by a sensorless brushless dc drive scheme. The experiment results are reported and show good correlation with the theory.
- Hulicova