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The ultrafast frequency response supercapacitor is a promising candidate for alternating current line filtering. We report the fabrication of a special structured ionic liquid-based supercapacitor with an ultrafast response of only 1.5 ms. The three-dimensional aluminum (Al) foam in situ coated with carbon layer (∼500 nm) serves as the novel, highly efficient electrode-current collector. The high porosity (95%) of Al foam allows the rapid ion diffusion and the as-obtained Al/C interface with atomic-level mixing allows the fast electron transfer, two crucial factors for ultrafast response. Hence, it possesses an excellent specific mass capacitance of 68 mF g-1 at 120 Hz, as well as an ultrahigh rate of up to 3000 V s -1. The supercapacitors exhibit frequency modulation performance in the range of 20 kHz to 16 MHz. They exhibit the similar even better alternating current filtering performance, as compared to the commercial aluminum electrolytic capacitors, detected at 10 Hz, 60 Hz, 100 Hz and 1 M Hz. These results suggest that, although ILs have high viscosity and low ion mobility, the IL-based supercapacitor has a great potential to be used as a device for alternating current line filtering, as well as providing nonvolatile and nonflammability safety.

Graphene/carbon nanotube (CNT)-based adsorbents were fabricated on a kilogram scale by extrusion processing (where graphene is used as the major adsorption material and CNTs make up the backbone to enhance the mechanical strength) and then mixed and bonded with poly(tetrafluoroethylene). Kilogram-scale adsorbents were used to treat the content of o-cresol in wastewater to be

Thick electrode was promising to increase the energy density in device (battery or supercapacitor) scale, but always suffered the ion polarization upon high rate discharge. We reported the use of 3D Al foam (current collector) to host graphene (with high surface area but very low packing density) to fabricate 450 ​μm thick electrode with mass loading of 10–15 ​mg ​cm−2. The space confinement effect of Al wires on graphene at any regions offered sufficient ordered diffusion channel of liquids, alleviating the ion polarization significantly, compared to the same thick graphene sheet pasted on 2D Al foil by simulation with COMSOL software. The 100 ​F pouch supercapacitor with ionic liquids at 4 ​V exhibited low contact resistance, high specific capacitance in a wide range of current densities, and simultaneously the volumetric energy density of 18 ​Wh L−1 and the power density of 5 ​kW ​kg−1, far better than those of current commercial device.

Carbon nanomaterials, mainly carbon nanotubes (CNTs) and graphene, have received much attention in the past two decades. With the maturity of preparation technology and performance studies, they have been gradually applied in the industries of lithium-ion batteries (as conductive agents) and supercapacitors (as the main electrode materials). The large-scale production (up to thousands of tons per year) of CNTs has been realized, and the production cost has been greatly reduced. The production of graphene also exceeds one hundred tons per year, requiring the same improvement in performance/cost ratio. As one of the cheapest hydrocarbons, methane serves as a feedstock of both CNTs and graphene. The catalytic methane technology via the chemical vapor deposition method is advantageous for the controlled synthesis and mass production of carbon materials with high yield, high quality and at low cost, which are necessary requirements for any potential yet competitive commercial applications. Firstly, the methane deposition of CNTs is discussed, with a brief introduction on the preparation of CNTs, then the growth mechanism of CNTs, thermodynamics of methane decomposition in CNT synthesis, catalysts to decompose methane for CNT growth, and the synthesis of CNTs with different structures from methane. Secondly, the methane deposition of graphene is discussed, with a brief introduction on the preparation of graphene, then the growth kinetics of graphene, the quality estimation of graphene, and the synthesis of graphene with different structures from methane. Finally, the reactor technology for the enhanced production of CNTs and graphene is introduced, including the large-scale production of powder-like CNTs and graphene, ultralong CNTs, and graphene films, respectively. The review is useful for understanding the scientific and engineering challenges in this field and for the large-scale production of these important carbon nanomaterials from methane in the future.

The development of supercapacitors with high energy density calls for multi-functional electrode materials without obvious drawbacks in capacitance performance and in device processing. The highly electroconductive mesoporous activated carbon fibers (MACFs) for 4 V supercapacitors in ionic liquids are proposed. Preparing by the controlled carbonization and activation of polyacrylonitrile-based fibers by CO2 at high temperature, MACFs exhibit high special surface area (2404 m2/g), large mesopore volume (2.3 cm3/g), large packing density (0.25 g/cm3), high electrical conductivity of 57–195 S/cm, good chemical stability at high voltage and low liquid intake ability. As tested in EMIMBF4 electrolyte at 4 V, MACFs exhibit high capacitance (204 F/g at 0.5 A/g), high energy density (113 Wh/kg) and excellent capability of capacitance retention. Such excellent capacitance performance is also due to the one-dimensional structure of MACFs, with the long carbon in-plane length for electron transfer in axial direction and the short radial diffusion distance for ions of ionic liquids. To the best of our knowledge, the obtained MACFs are the first material combining all advantages of conventional electrode material (activated carbon) and new generation electrode materials (mainly carbon nanotubes and graphene) together, as well as minimizing their major drawbacks.

This paper is aimed to seek for the optimized composite microstructure for highest material usage efficiency. An energy-measured material usage efficiency is proposed as the criterion for structural optimization design, and we believe it is the best choice among all single parameters to evaluate the performance. The staggered bio-composites consisting of rectangular platelets and soft matrix have been widely studied, and proved to possess good mechanical properties. It is found that this staggered structure can be further optimized to achieve higher material usage efficiency. Based on the shear-lag analysis, the optimization shows that the optimal platelet shape is rhombic, which leads to more uniform stresses in both the platelet and the matrix compared with the widely used platelet shape, i.e. rectangle. The rhombic platelet case also possesses higher stiffness and strength than that of the rectangular platelet case.

The use of carbon nanotube- and graphene-based nanomaterials as a high-performance electrode is one of the promising directions when it comes to developing high-voltage supercapacitors with both a high power density and high energy density. However, the mass production and post-treatment of the carbon nanotube/graphene-based nanomaterials with high purity are necessary steps toward the commercialization of high-performance supercapacitors, and the challenges in engineering carbon nanotube/graphene-based nanomaterials for device-scale supercapacitors also need to be considered. In this review, the authors first introduce the chemical vapor deposition for large-scale preparation of carbon nanotube/graphene-based nanomaterials and the exfoliation method for graphene, which are followed by the methods used to purify these nanomaterials. Then, the capacitance performance of the carbon nanotube/graphene-based nanomaterials in the electrolytes of a high-voltage window is discussed, including the discussion of the capacitance limit of sp2 carbon materials, as well as a comparison of the capacitance performance in ionic liquids electrolytes with that in organic electrolytes and a discussion of low-temperature performance. Finally, the challenges in fabricating supercapacitor devices, such as the intake of excess liquids, the densification of carbon nanotube/graphene-based electrodes, and the reduction of the resistance of supercapacitors, are addressed.

Two-dimensional (2D) layered materials with a non-centrosymmetric structure exhibit great potential for nano-scale electromechanical systems and electronic devices. Piezoelectric and ferroelectric 2D materials draw growing interest for applications in energy harvesting, electronics, and optoelectronics. This article first reviews the preparation of these functional 2D layered materials, including exfoliation methods and vapor phase deposition growth, followed by a general introduction to various piezo/ferro-electric characterization methods. Typical 2D piezoelectric and ferroelectric materials and their electronic properties, together with their potential applications, are also introduced. Finally, future research directions for 2D piezoelectric and ferroelectric materials are discussed.

We report the fabrication of mesoporous tubular graphene (MTG) by a chemical vapor deposition method using MgO@ZnO core-shell structure as the template. The unique bi-directional ions transfer in unstack graphene layers and high mesopore ratio of MTGs allows capacitance reach 15 μF/cm2 at 0.5 A/g, and 11 μF/cm2 at 10 A/g, which is closer to theoretical value (21 μF/cm2) than SWCNTs and DWCNTs at either low or high rate. Meanwhile, MTGs exhibited good structural stability, high surface area (701 m2/g), high conductivity (30 S/cm) and low oxygen ratio (0.7 atom%), allowing excellent SC performance. The 4 V EDLC using MTGs and EMIMBF4 electrolyte exhibited high energy density in wide range of high power density and excellent cycling stability, showing strong potential in EDLC and other electrochemical energy storage systems, in addition, showing significant factor of ion transfer distance for high performance SCs especially operating at high voltage using ionic liquid electrolyte.

Enriching the functionality of ferroelectric materials with visible-light sensitivity and multiaxial switching capability would open up new opportunities for their applications in advanced information storage with diverse signal manipulation functions. We report experimental observations of robust intralayer ferroelectricity in two-dimensional (2D) van der Waals layered α-In2Se3 ultrathin flakes at room temperature. Distinct from other 2D and conventional ferroelectrics, In2Se3 exhibits intrinsically intercorrelated out-of-plane and in-plane polarization, where the reversal of the out-of-plane polarization by a vertical electric field also induces the rotation of the in-plane polarization. On the basis of the in-plane switchable diode effect and the narrow bandgap (∼1.3 eV) of ferroelectric In2Se3, a prototypical nonvolatile memory device, which can be manipulated both by electric field and visible light illumination, is demonstrated for advancing data storage technologies.

Developing an ionic-liquid (IL) type electrolyte with both high voltage window and wide temperature window, especially the low temperature range, is crucial to increase the energy density of the associated electrical double layer capacitors. We proposed the addition of γ-butyrolactone (GBL) in EMIMBF4 to form a binary electrolyte. The melting point (∼15 °C) of EMIMBF4 disappeared and the glass transition point decreased from −95 °C (for pure EMIMBF4) to −126 °C for the binary electrolyte. The binary electrolyte also exhibited improved ionic conductivity (26 and 0.31 mS cm−1 at 20 and −70 °C, respectively) and allowed an electrode of mesoporous graphene to exhibit a capacitance of 131 F g−1 and energy density of 61 W h kg−1 at −70 °C and 3.7 V, the highest values reported so far. NMR and ATR-IR characterization validated the strong interaction between GBL and EMIMBF4 for breaking the ion pairs of the latter but without forming the solvated ions, as in the system of EMMIBF4 with propylene carbonate.

Developing nanostructured adsorbents of organics is crucial for environmental protection with low energy consumption, but care needs to be taken to prevent the loss of nanomaterials because of their small size. This paper reports the fabrication of carbon nanotube (CNT)-alumina strips (CASs) with a high surface area, sufficient mesopores and strongly interacted structure. Use of CASs allowed the rapid and reversible adsorption–desorption of para-xylene, when compared to pristine powders of CNT and activated carbon. Use of CASs is promising for the practical use when packed in a scaled adsorption tower.

Stronger, tougher, and lighter materials are always among the relentless pursuits of material scientists and engineers. The hierarchical design inspired by nature has been considered as one of the most promising strategies to improve the mechanical properties and functionalities of synthetic materials beyond their present limitations. Therefore, this paper provides a featured review on mechanical studies of hierarchical composite materials, including natural biological materials as well as man-made materials, to shed light on the progress and perspectives of this research field. This review first discusses several typical hierarchical designs observed in nature, followed by four principle mechanisms extracted as the main contributions to the superior mechanical properties. Then, the applications of these principle mechanisms are demonstrated in three typical synthetic material systems, namely, fiber-reinforced composites, network materials, and mechanical metamaterials. Furthermore, the remaining challenges and future perspectives for the design and optimization of hierarchical composites are proposed.

The treatment of organic wastewater is of great significance. Carbon nanotube (CNT)/graphene-based nanomaterials have great potential as absorbent materials for organic wastewater treatment owing to their high specific surface area, mesoporous structure, tunable surface properties, and high chemical stability; these attributes allow them to endure harsh wastewater conditions, such as acidic, basic, and salty conditions at high concentrations or at high temperatures. Although a substantial amount of work has been reported on the performance of CNT/graphene-based nanomaterials in organic wastewater systems, engineering challenges still exist for their practical application. Herein, the adsorption mechanism of CNT- and graphene-based nanomaterials is summarized, including the adsorption mechanism of CNTs and graphene at the atomic and molecular levels, their hydrophilic and hydrophobic surface properties, and the structure-property relationship required for adsorption to occur. Second, the structural modification and recombination methods of CNT- and graphene-based adsorbents for various organic wastewater systems are introduced. Third, the engineering challenges, including the molding of macroscopically stable adsorbents, adsorption isotherm models and adsorption kinetic behaviors, and reversible adsorption performance compared to that of activated carbon (AC) are discussed. Finally, cost issues are discussed in light of scalable and practical application of these materials.

Graphene is a hot star in materials science with various potential application aspects, including in Li-ion battery and supercapacitor. The burst of scientific papers in this area seems to validate the performance of graphene, but also arouses large dispute. Herein, we share our judgment of these trends to all, encouraging the discussion and enhancing the understanding of the structure-performance relationship of graphene.

We studied the full capacitance potential of single-walled carbon nanotube (SWCNT, 1250 m2 g−1) in EMIBF4 at 4 V by a new charge mode with certain dwelling time at 4 V. This allowed the accessible surface area of SWCNT, in monodispersed state and with macropores in large amount, to be fully explored to exhibit capacitance of 16 μF cm−2 in a wide range of current density, which is higher than that (9.1 μF cm−2) of graphene (5 μm in size and 2200 m2 g−1). In situ Raman characterization upon charge and discharge validated the enhanced doping of ions of EMIBF4 on SWCNT wall with the increased potential. The energy density is found to be 107 W h kg−1 at the power density of 20 kW kg−1, far exceeding that (64 W h kg−1) in conventional galvanostatic charge and discharge mode.

Polyethylene was crystallized on carbon nanotubes (CNTs) resulting in the formation of nanosheets on the surface. The material was then carbonized in sulfuric acid at 20 °C for 24 h, resulting in a carbon shish-kebab (CSK) structure. Incorporating the CSKs in polyimide (PI) matrix produced a uniform dispersion in which interactions between the nodules producing an interlocking effect that significantly improved the load transfer between the matrix and the CNTs. Consequently, the CSK/PI composite showed a 27% increase in tensile strength, compared to one using pristine CNTs, and 100% increase in the strain compared to the pure PI membrane.

The formation of carbon encapsulated Fe nanoparticles (Fe@C), in the process of growing single-/double- walled carbon nanotubes (S/DWCNTs) from methane was investigated by quantitatively analyzing the samples at different reaction time. We found that the ratio of Fe@C to the total Fe sustainably increased after the terminated growth of S/DWCNTs. We proposed that thin graphite layers produced in the middle stage of the reaction, as a mechanical barrier, covered the surface of MgO support and prevented Fe nanoparticles from contacting carbon source for the growth of S/DWCNTs via the root growth mode. These results suggested that the synthesis of desirable S/DWCNTs and undesirable Fe@C impurities was a consecutive process, not a paralleled one as proposed in many previous works. It provided useful information for the controlled synthesis of S/DWCNTs with high purity and high selectivity.

We report a novel method to prepare nanohybrid shish-kebab (NHSK) structure of polyethylene (PE) and carbon nanotube (CNT). Pristine CNTs without surface modification with high concentration was effectively dispersed in xylene solution by a simple shearing method, which induces the quick crystallization of PE in xylene to form a novel NHSK structure with more dense and smaller PE kebab on CNT axis. The flocculated NHSK product was transferred quickly from the xylene solution to the ethanol solution, in order to shorten the preparation time. The freeze-drying method was used in vacuum instead of high-temperature drying to avoid the aggregation of NHSK product. These improvements allow the formation of NHSK with an absolute yield of 200 mg·h−1, which is 2000 folds of that reported previously. It is favorable to apply this structured material in high performance nanocomposite, by improving the compatibility of CNTs in polymer and the interfacial force between CNTs and polymer.

We reported the fabrication of a hierarchical carbon nanotube (CNT) membrane by using the 90% granulated double- or triple-walled CNTs and 10% 100 μm long multiwalled CNTs as the linker. The membrane with packing density of 420 kg/m3, excellent electrical conductance and good mechanical strength, functioned as both the electrode and current collector and allowed the weight ratio of CNTs increased up to 45–50% based on the weight of CNT, electrolyte and separator. The granulated double or triple walled CNTs, by the aggregation at high temperature etching using CO2, simultaneously exhibited high surface area and tunable pore structure and high pore volume, and were favorable for the ion transport of organic electrolyte, due to the effect of opening cap or side wall by the CO2. The CNT membrane electrode, exhibited the capacitance of 57.9 F/g and the energy density of 35 W h/kg, as operated at 4 V.

Addition of a single walled carbon nanotube in ionic liquids of EMIBF4 produced a nanofluid with increased ionic conductivity. It, as the electrolyte, allowed the increase of the capacitance, energy density and cycling stability of a supercapacitor operated at 4 V.

For the synthesis of single-walled carbon nanotubes (SWCNTs) from CH4 over a Fe/MgO catalyst, we proposed a coupled Downer-turbulent fluidized-bed (TFB) reactor to enhance the selectivity and yield (or production rate) of SWCNTs. By controlling a very short catalyst residence time (1–3 s) in the Downer, only part of Fe oxides can be reduced to form Fe nano particles (NPs) available for the growth of SWCNTs. The percentage of unreduced Fe oxides increased and the yield of SWCNTs decreased accordingly with the increase of catalyst feeding rate in Downer. SWCNTs were preferentially grown on the catalyst surface and inhibited the sintering of the Fe crystallites which would be formed thereafter in the downstream TFB, evidenced by TEM, Raman and TGA. The coupled Downer-turbulent fluidized-bed reactor technology allowed higher selectivity and higher production rate of SWCNTs as compared to TFB alone.