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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.

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.

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.

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.

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 report the fabrication of one-dimensional highly electroconductive mesoporous graphene nanofibers (GNFs) by a chemical vapor deposition method using MgCO3·3H2O fibers as the template. The growth of such a unique structure underwent the first in situ decomposition of MgCO3·3H2O fibers to porous MgO fibers, followed by the deposition of carbon on the MgO surface, the removal of MgO by acidic washing, and the final self-assembly of wet graphene from single to double layer in drying process. GNFs exhibited good structural stability, high surface area, mesopores in large amount, and electrical conductivity 3 times that of carbon nanotube aggregates. It, used as an electrode in a 4 V supercapacitor, exhibited high energy density in a wide range of high power density and excellent cycling stability. The short diffusion distance for ions of ionic liquids electrolyte to the surface of GNFs yielded high surface utilization efficiency and a capacitance up to 15 μF/cm(2), higher than single-walled carbon nanotubes.

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.