Electrodes that have high electrical conductivity, large ion-accessible area and good mechanical robustness are highly needed for developing high-performance flexible supercapacitors. Herein, we report the preparation of a carbon nanotube (CNT) hybrid film consisting of large-diameter multi-walled carbon nanotubes (MWCNTs) and small-diameter single-walled carbon nanotubes (SWCNTs) and its application as an electrode for flexible supercapacitors. In the hybrid film, MWCNTs provide a macroporous and robust scaffold while SWCNTs bridge MWCNTs and improve the film's strength and electrical conductivity. Resulting from such a hierarchical structure that could facilitate ion transportation inside of the electrode, the specific capacitance of SWCNTs loaded in hybrid films was increased by about 273% when compared with that of SWCNT films. A thin layer of polyaniline was electrochemically deposited on the hybrid film, forming a composite film with good structural flexibility and high capacitance. Solid-state symmetric supercapacitors assembled using such a composite film electrode showed good rate performance and high cycling stability.

Pseudocapacitive symmetric supercapacitors, where both the cathode and the anode have the same pseudocapacitive material, have been widely investigated for developing high-performance supercapacitors. However, being different from electrochemical double-layer (EDL) capacitive electrodes, the charge storage of pseudocapacitive materials relies on reversible redox reactions that change the ion valence status, which is not the case for EDL capacitors (EDLCs). In this research, as a typical inorganic pseudocapacitive material for supercapacitors, a manganese dioxide (MnO2) based symmetric supercapacitor was carefully investigated by using a flexible and ultra-light carbon nanotube (CNT) film as the current collector and substrate for MnO2 electrodeposition. The results indicated that the pristine active material on the positive electrode showed no change after cyclic charging/discharging, but only served as a stable counter electrode and reference electrode. The main redox reaction for the energy storage of the supercapacitor occurred on the negative electrode. Furthermore, the dissolved Mn2+ ions on the negative electrode were deposited onto the positive electrode, which induced an increase in mass of the positive electrode and a decrease in mass of the negative electrode. This research could give new insight into the working mechanism of MnO2 electrodes and other pseudocapacitive materials in symmetric supercapacitors.

Carbon nanotube (CNT) film is a favorable kind of substrate in flexible electric devices because of its superior flexibility, favorable mechanical strength and excellent electrical conductivity. Moreover, since the conductive polymer polyaniline (PANI) possesses a high capacitance and is easy to manufacture, it is always a favored material in the field of supercapacitors. In this research, CNT film synthesized via a floating catalyst chemical vapor deposition method could be further activated by its electrochemical re-expansion to achieve better porosity and higher specific area, in order to obtain an all-solid-state flexible supercapacitor with a higher area capacitance. In comparison with the pristine CNT film decorated with PANI, electrochemically fabricated CNT hydrogel film with PANI deposition had a higher specific area capacitance of 680 mF cm−2 at 1 mA cm−2. The all-solid-state supercapacitor that was synthesized from this composite film exhibited a high specific area capacitance of 184.6 mF cm−2 at 1 mA cm−2, which was higher than many similar supercapacitors. The rolling test showed that this supercapacitor maintained its high capacitance even under conditions of rolling. After 500 charge–discharge cycles, it also retained its high coulombic efficiency and specific area capacitance. This all-solid-state supercapacitor shows great potential in the field of energy storage devices.

Large-diameter carbon nanotube (CNT) paper was used as a porous and conductive template to obtain vertically aligned Ni2(OH)2CO3 nanowire array shells, which could be further converted into highly active Ni(OH)2 nanosheets by a cyclic voltammetry strategy. The as-prepared hierarchical nanostructure showed superior electrochemical performance for the electrodes of supercapacitors.

Metal sulfides are an emerging class of high-performance electrode materials for electrochemical energy storage devices. Here, a facile hydrothermal method is reported to assemble three-dimensional (3D) NiS-reduced graphene oxide (rGO) hybrid aerogels with strong coupling between the two compounds. It is intriguing to note that NiS nanoparticles are well anchored on the 3D porous and conductive scaffold constructed from wrinkled rGO nanosheets. When evaluated as binder-free electrode materials for supercapacitors, impressive electrochemical performances are presented. Specifically, the 3D NiS–rGO aerogel nanocomposite exhibits a high capacitance of 852 F g−1, 526 F g−1 based on the whole electrode mass (mNiS:mGO = 45 mg/50 mg) at a current density of 2 A g−1 and 15 A g−1, respectively. These satisfactory electrochemical behaviors, attributed to the introduction of reduced graphene oxide, suggest the great promise of fabricating graphene-supported hybrid electrode materials for high-performance energy applications.

MnO2 has ultra-low conductivity for electrodes of supercapacitors. In this research, porous reduced graphene oxide (rGO) wraps on MnO2 nanoflowers with a conductive carbon nanotube core (CNT–MnO2). This nanostructure could effectively improve the surface and inner conductivity of the composites. Unlike pristine rGO, the porous rGO does not block the diffusion of electrolyte into the inner part of the composites, which allows the utilization of MnO2 in this composite capacitor very well. As a result, the as-prepared CNT–MnO2–porous rGO ternary hybrid material shows superior specific capacitance and rate performance to pristine CNT–MnO2 nanocables and pristine rGO wrapped CNT–MnO2 nanocables. This synthesis strategy could be valuable for the design of better performance pseudocapacitive electrodes for supercapacitors.

•We fabricate porous carbon nanofiber mat with single-walled carbon nanotubes.•An electrospinning-carbonization strategy was used.•The composite shows good electrochemical performance.Active carbon nanofibers (CNFs) with porous structure show highly electrochemical double-layer capacitance for supercapacitors because of their large specific area. However, their poor crystallization induced the low conductivity, which could largely limit the electrochemical performance of the porous CNFs. In this research, porous CNFs with single-walled carbon nanotubes (SWCNTs) were prepared by electrospinning and high temperature carbonization. The introduction of SWCNTs into porous CNFs could largely enhance the conductivity of the porous CNF nanotextiles, thus the electrochemical performance of the composite nanotextile was largely enhanced. The specific capacitance of the composite could achieve 417 F/g at a current density of 0.5 A/g, and keep 193 F/g at the high current density of 10 A/g. Furthermore its specific capacitance could keep 96% after 2000 cycles of charge/discharge at the current density of 10 A/g. This nanotextile could be a promising candidate for the binder-free and filler-free electrodes of high-performance supercapacitors.

The mass integration of electrochemically active materials on nanosized conductive fillers is a promising strategy to achieve an ideal electrode structure for energy storage devices. In this research, a one-dimensional CNT@NiCo2O4 nanosheet core–shell structural nanocable was constructed by a facile chemical co-deposition route combined with post-calcination in air. The subsequent thermal treatment led to the transformation of the hydroxide nanosheet precursor to NiCo2O4 nanosheets, during which process the overall morphology and structure were well retained. By selecting CNTs as conductive support for ultra-thin NiCo2O4 nanosheets, a high-performance electrode for supercapacitors was obtained. Notably, the as-prepared CNT@NiCo2O4 nanocables have a high capacitance of 1038 F g−1 at a current density of 0.5 A g−1. Furthermore, the specific capacitance of the product was almost 100% retained after 1000 cycles, which indicates excellent structural and cycling stability. More importantly, a relatively high mass loading of active materials on CNTs was also achieved, making the practical application of such electrode materials possible. Consequently, this CNT@NiCo2O4 nanocable is a promising electrode for high-performance supercapacitors.

Carbon nanotube (CNT) arrays show great promise in developing anisotropic thermal conductive composites for efficiently dissipating heat from high-power devices along thickness direction. However, CNT arrays are always grown on some substrates and liable to be deformed and broken into pieces during transfer and solution treatment. In the present study, we intentionally synthesized well-crystallized and large-diameter (∼80 nm) multiwalled CNT (MWCNT) arrays by floating catalyst chemical vapor deposition (FCCVD) method. Such arrays provided high packing density and robust structure from collapse and crack formation during post solution treatment and therefore favored to maintain original thermal and electrical conductive paths. Under optimized condition, the CNT arrays can be transferred into flexible composite films. Furthermore, the composite film also exhibited excellent thermal conductivity at 8.2 W/(m·K) along thickness direction. Such robust, flexible, and highly thermal conductive composite film may enable some prospective applications in advanced thermal management.Keywords: carbon nanotube array; crack-free; flexible; highly thermal conductive; scalable transfer;

Herein, we demonstrate the high-density assembly of Ni–Co hydroxide nanoflakes on conductive carbon nanotube (CNT) network through a simple and rapid chemical precipitation method, presenting a low-cost and high-performance scaffold for pseudosupercapacitor. It is found that the Ni–Co layered double hydroxide (LDH) nanoflakes prefer to proliferate around large-diameter CNTs (diameter > 50 nm), with conductive CNT network well-maintained. Such hierarchical nanostructures show greatly improved specific surface areas compared with bare CNT network and are freestanding without other organic binder, which can be directly employed as a binder-free compact electrode assembly. By optimizing the chemical composition of as-precipitated LDH nanoflakes, the resultant Co0.4Ni0.6(OH)2 LDH/CNT composite nanostructures exhibit the largest specific electrochemical capacitance and the best rate performance, with their capacitance up to 1843 F/g under a low current density of 0.5 A/g and maintained at 1231 F/g when the current density is increased 20 times to 10 A/g. Importantly, such hierarchical nanostructures tend to prevent the electrode from severe structural damage and capacity loss during hundreds of charge/discharge under a high rate (2 A/g), ensuring the electrode with high-energy density (51 W h/kg) at power density of 3.3 kW/kg.Keywords: carbon nanotube paper; hierarchical nanowire; layered double hydroxide; nanoflake; supercapacitor

•We fabricate hierarchical carbon nanotube/α-Ni(OH)2 nanosheet composite paper.•A facile chemical bath deposition was used.•The composite paper shows good electrochemical performance.Carbon nanotube (CNT)/α-Ni(OH)2 composite paper based on CNT paper was prepared by a facile chemical bath deposition (CBD) method. α-Ni(OH)2 nanosheets were vertically grown on individual CNTs in CNT paper to form hierarchical nanowires. The loading mass of α-Ni(OH)2 in the composite paper could be 66 wt%. Thus the composite paper showed much higher specific surface area than that of pristine CNT paper. This novel structure brings the composite paper an electrochemical capacitance high to 1144 F/g at the current density of 0.5 A/g, and maintains 585 F/g at 10 A/g. This composite paper could be a promising candidate for the electrodes of high-performance supercapacitors.

MnO2 has been widely studied as the pseudo-capactive electrode material of high-performance supercapacitors for its large operating voltage, low cost, and environmental friendliness. However, it suffers from low conductivity and being hardly handle as the electrodes of supercapacitors especially with flexibility, which largely limit its electrochemical performance and application. Herein, we report a novel ternary composite paper composed of reduced graphene sheet (GR)-patched carbon nanotube (CNT)/MnO2, which has controllable structures and prominent electrochemical properties for a flexible electrode of the supercapacitor. The composite paper was prepared by electrochemical deposition of MnO2 on a flexible CNT paper and further adsorption of GR on its surface to enhance the surface conductivity of the electrode and prohibit MnO2 nanospheres from detaching with the electrode. The presence of GR was found remarkably effective in enhancing the initial electrochemical capacitance of the composite paper from 280 F/g to 486.6 F/g. Furthermore, it ensures the stability of the capacitance after a long period of charge/discharge cycles. A flexible CNT/polyaniline/CNT/MnO2/GR asymmetric supercapacitor was assembled with this composite paper as an electrode and aqueous electrolyte gel as the separator. Its operating voltage reached 1.6 V, with an energy density at 24.8 Wh/kg. Such a composite structure derived from a multiscale assembly can offer not only a robust scaffold loading MnO2 nanospheres but also a conductive network for efficient ionic and electronic transport; thus, it is potentially promising as a novel electrode architecture for high-performance flexible energy storage devices.Keywords: buckypaper; carbon nanotube; graphene; MnO2; supercapacitor;

Active carbon (AC) is a widely used electrode material for electrochemical double layer capacitors (EDLCs). However, it often shows poor rate capability due to its low conductivity. Herein, we report a binder-free carbon nanomaterials hybrid structure formed by core-shell structural nanowire network, in which carbon nanotube (CNT) buckypaper serves as conductive scaffold and porous AC layer is coated on individual CNTs in the buckypapers as active component for capacitance contribution. Such hybrid structure shows a greatly enhanced rate performance compared to pure CNT and AC electrode with its electrochemical capacitance better than its two components at large charge/discharge current densities. The AC layer in this hybrid buckypaper, which is as the main component contributed to the electrochemical capacitance, shows good rate performance and enhanced electrochemical capacitance at large current density. The performance improvement arises from the integration of resultant highly porous AC layer, conducting network and good interfacial contact between AC coating and CNTs, favoring the efficient transport of ions and electrons over the electrode surface. Moreover, the assembled EDLC with such hybrid buckypaper electrode also present higher and more stable energy densities with the increase of power densities compared to AC based EDLC.Highlights► We fabricated novel CNT@active carbon core-shell structural nanowire buckypaper. ► The synthetical method was facile. ► Active carbon and CNT had good contact. ► The composite buckypaper showed good electrochemical performance as the electrodes of supercapacitors. ► The electrochemical performance of active carbon was furthest exerted in this structure.

β-SiC nanoparticle reinforced Al matrix (nano-SiCp/Al) composite was prepared by a multistep powder metallurgy strategy including presureless sintering, hot compacting process and hot extrusion. The microstructures of the as-prepared composites were observed by scanning electronic microscopy (SEM), and the mechanical properties were characterized by tensile strength measurement and Brinell hardness test. The experimental results revealed that the tensile strength of the composite with the addition of 5wt% β-SiC nanoprticles could be increased to 215 MPa, increasing by 110% compared with pure Al matrix. Comparative experiments reflected that the β-SiC nanoprticles showed significant reinforcement effect than traditional α-SiC micro-sized particles. The preparation process and sintering procedure were investigated to develop a cost effective preparation strategy to fabricate nano-SiCp/Al composite.

Carbon nanotube (CNT) buckypaper, which has large specific surface area and tunable network structures, shows great potential in the application of heat dissipation for high power electronic devices. In this article, we report that the heat conduction in a buckypaper depends greatly on CNT network formation, in which CNT structures, lengths, and orientations are important issues. The buckypaper composed of multiwalled CNTs with large diameter (around 50 nm) and suitable length (1–10 μm) shows lower thermal impedance compared with those made by longer CNTs with smaller diameter. The thermal impedance of such buckypapers can be reduced to 0.27 cm2·K/W, lower than that of commercialized graphite foil and thermal grease. Thus, the buckypaper may serve as a promising candidate for advanced thermal interface materials. Detailed structural characterization indicates that the three-dimensional networks of buckypapers, with CNT orientations perpendicular to the surfaces, result in both the reduction of thermal contact resistance and the enhancement of heat conduction along the thickness.

Large-diameter carbon nanotube (CNT) paper was used as a porous and conductive template to obtain vertically aligned Ni2(OH)2CO3 nanowire array shells, which could be further converted into highly active Ni(OH)2 nanosheets by a cyclic voltammetry strategy. The as-prepared hierarchical nanostructure showed superior electrochemical performance for the electrodes of supercapacitors.

The mass integration of electrochemically active materials on nanosized conductive fillers is a promising strategy to achieve an ideal electrode structure for energy storage devices. In this research, a one-dimensional CNT@NiCo2O4 nanosheet core–shell structural nanocable was constructed by a facile chemical co-deposition route combined with post-calcination in air. The subsequent thermal treatment led to the transformation of the hydroxide nanosheet precursor to NiCo2O4 nanosheets, during which process the overall morphology and structure were well retained. By selecting CNTs as conductive support for ultra-thin NiCo2O4 nanosheets, a high-performance electrode for supercapacitors was obtained. Notably, the as-prepared CNT@NiCo2O4 nanocables have a high capacitance of 1038 F g−1 at a current density of 0.5 A g−1. Furthermore, the specific capacitance of the product was almost 100% retained after 1000 cycles, which indicates excellent structural and cycling stability. More importantly, a relatively high mass loading of active materials on CNTs was also achieved, making the practical application of such electrode materials possible. Consequently, this CNT@NiCo2O4 nanocable is a promising electrode for high-performance supercapacitors.

Carbon nanotube (CNT) film is a favorable kind of substrate in flexible electric devices because of its superior flexibility, favorable mechanical strength and excellent electrical conductivity. Moreover, since the conductive polymer polyaniline (PANI) possesses a high capacitance and is easy to manufacture, it is always a favored material in the field of supercapacitors. In this research, CNT film synthesized via a floating catalyst chemical vapor deposition method could be further activated by its electrochemical re-expansion to achieve better porosity and higher specific area, in order to obtain an all-solid-state flexible supercapacitor with a higher area capacitance. In comparison with the pristine CNT film decorated with PANI, electrochemically fabricated CNT hydrogel film with PANI deposition had a higher specific area capacitance of 680 mF cm−2 at 1 mA cm−2. The all-solid-state supercapacitor that was synthesized from this composite film exhibited a high specific area capacitance of 184.6 mF cm−2 at 1 mA cm−2, which was higher than many similar supercapacitors. The rolling test showed that this supercapacitor maintained its high capacitance even under conditions of rolling. After 500 charge–discharge cycles, it also retained its high coulombic efficiency and specific area capacitance. This all-solid-state supercapacitor shows great potential in the field of energy storage devices.