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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.

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.

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.