The sp²-hybridized nanocarbon (e.g., carbon nanotubes (CNTs) and graphene) exhibits extraordinary mechanical strength and electrical conductivity but limited external accessible surface area and a small amount of pores, while nanostructured porous carbon affords a huge surface area and abundant pore structures but very poor electrical conductance. Herein the rational hybridization of the sp² nanocarbon and nanostructured porous carbon into hierarchical all-carbon nanoarchitectures is demonstrated, with full inherited advantages of the component materials. The sp² graphene/CNT interlinked networks give the composites good electrical conductivity and a robust framework, while the meso-/microporous carbon and the interlamellar compartment between the opposite graphene accommodate sulfur and polysulfides. The strong confinement induced by micro-/mesopores of all-carbon nanoarchitectures renders the transformation of S₈ crystal into amorphous cyclo-S₈ molecular clusters, restraining the shuttle phenomenon for high capacity retention of a lithium-sulfur cell. Therefore, the composite cathode with an ultrahigh specific capacity of 1121 mAh g⁻¹ at 0.5 C, a favorable high-rate capability of 809 mAh g⁻¹ at 10 C, a very low capacity decay of 0.12% per cycle, and an impressive cycling stability of 877 mAh g⁻¹ after 150 cycles at 1 C. As sulfur loading increases from 50 wt% to 77 wt%, high capacities of 970, 914, and 613 mAh g⁻¹ are still available at current densities of 0.5, 1, and 5 C, respectively. Based on the total mass of packaged devices, gravimetric energy density of GSH@APC-S//Li cell is expected to be 400 Wh kg⁻¹ at a power density of 10 000 W kg⁻¹, matching the level of engine driven systems.

The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) play a decisive role for the efficiency of fuel cells and metal-air batteries. The nitrogen doped carbon materials with low cost and long durability are potential catalysts to replace precious metal catalyst for oxygen electrochemistry; however, the unexposed active sites induced by the bulk dopant atoms are hardly accessible and consequently scarcely contribute to the catalytic property. In this study, carbon nanotubes (CNTs) are selected as the platform to demonstrate the potential of full exposure of ‘active sites’ at the surface. Novel N-doped carbon coaxial nanocables with the pristine CNTs as the core and the N-doped carbon layers as the shell are proposed. The accessible and efficient utilization of the integrated nitrogen atoms enriched on the surface, together with the undestroyed intact inner walls, render the electrocatalyst much enhanced electrocatalytic activity and high electrical conductivity of 3.3 S cm⁻¹, therefore, N-doped nanocables afford higher oxygen reduction current, ∼51 mV positively shift onset potential, low peroxide generation, as well as lower overpotential and higher current for oxygen evoluation reaction.

Nitrogen-doped carbon nanotubes (N-CNTs) are found to be active as one novel heterogeneous catalyst for acetylene hydrochlorination reaction, possessing good activity (TOF=2.3×10⁻³ s⁻¹) and high selectivity (>98 %). Compared to toxic and energy-consuming conventional catalysts, such as HgCl₂, N-CNTs are more favorable in terms of sustainability, because of their thermo-stability, metal-free make up, and the wide availability of bulk CNT. Coupling X-ray photoelectron spectroscopy and density functional theory computations (DFT), the main active source and reaction pathway are shown. Good linearity between the quaternary nitrogen content and conversion is revealed. DFT study shows that the nitrogen doping enhanced the formation of the covalent bond between C₂H₂ and NCNT compared with the undoped CNT, and therefore promoted the addition reaction of the C₂H₂ and HCl into C₂H₃Cl.

The high-end applications of single-walled carbon nanotubes (SWCNTs) are hindered by the existence of large amount of impurities, especially the graphene layers encapsulating metal nanoparticles (metal@C NPs). The role of working metal catalysts during chemical vapor deposition (CVD) growth and post purifications by oxidation are not yet fully understood. Herein, the in situ monitoring the role of working metal catalyst NPs for ultrahigh purity SWCNTs by CVD growth and CO₂ purifications is carried out in an online thermogravimetric reactor attached with a mass spectrometer. The growth of SWCNTs almost stops after the initial 2 min, then, the mass increase of the samples mainly originates from the metal@CNP formation. Therefore, high-purity SWCNTs (98.5 wt%) with few metal@CNPs can be available by 2 min CVD growth. Furthermore, CO₂ oxidation of the SWCNTs is also investigated in a thermogravimetric reactor. The oxidation of graphene layers surrounding the metal NPs and the SWCNTs occurs during distinct temperature ranges, which is further demonstrated by the significant differences among their oxidation activation energies. Ultrahigh purity of SWNCT with a carbon content of 99.5 wt% can be available by a CO₂-assited purification method. The in situ study of the CVD growth and CO₂ oxidation of SWCNTs provides the real time information on the working catalyst during reaction and the reactivity information of metal@CNPs and SWCNTs under an oxidizing atmosphere. The success for the preparation of high-purity SWCNT lies in the efficient growth of SWCNTs with a low amount of nanocarbon impurities and partial oxidation of metal@CNPs by catalytic CO₂ oxidation with proper operation parameters.

The combination of one-dimensional and two-dimensional building blocks leads to the formation of hierarchical composites that can take full advantages of each kind of material, which is an effective way for the preparation of multifunctional materials with extraordinary properties. Among various building blocks, nanocarbons (e.g., carbon nanotubes and graphene) and layered double hydroxides (LDHs) are two of the most powerful materials that have been widely used in human life. This Feature Article presents a state-of-the-art review of hierarchical nanocomposites derived from nanocarbons and LDHs. The properties of nanocarbons, LDHs, as well as the combined nanocomposites, are described first. Then, efficient and effective fabrication methods for the hierarchical nanocomposites, including the reassembly of nanocarbons and LDHs, formation of LDHs on nanocarbons, and formation of nanocarbons on LDHs, are presented. The as-obtained nanocomposites derived form nanocarbons and LDHs exhibited excellent performance as multifunctional materials for their promising applications in energy storage, nanocomposites, catalysis, environmental protection, and drug delivery. The fabrication of LDH/carbon nanocomposites provides a novel method for the development of novel multifunctional nanocomposites based on the existing nanomaterials. However, knowledge of their assembly mechanism, robust and precise route for LDH/nanocarbon hybrid with well designed structure, and the relationship between structure, properties, and applications are still inadequate. A multidisciplinary approach from the scope of materials, physics, chemistry, engineering, and other application areas, is highly required for the development of this advanced functional composite materials.

Our society requires new materials for a sustainable future, and carbon nanotubes (CNTs) are among the most important advanced materials. This Review describes the state-of-the-art of CNT synthesis, with a focus on their mass-production in industry. At the nanoscale, the production of CNTs involves the self-assembly of carbon atoms into a one-dimensional tubular structure. We describe how this synthesis can be achieved on the macroscopic scale in processes akin to the continuous tonne-scale mass production of chemical products in the modern chemical industry. Our overview includes discussions on processing methods for high-purity CNTs, and the handling of heat and mass transfer problems. Manufacturing strategies for agglomerated and aligned single-/multiwalled CNTs are used as examples of the engineering science of CNT production, which includes an understanding of their growth mechanism, agglomeration mechanism, reactor design, and process intensification. We aim to provide guidelines for the production and commercialization of CNTs. Although CNTs can now be produced on the tonne scale, knowledge of the growth mechanism at the atomic scale, the relationship between CNT structure and application, and scale-up of the production of CNTs with specific chirality are still inadequate. A multidisciplinary approach is a prerequisite for the sustainable development of the CNT industry.

Three-dimensional hierarchical nanocomposites consisting of one-dimensional carbon nanotubes (CNTs) and two-dimensional lamellar flakes (such as clay, layered double hydroxides) show unexpected properties for unique applications. To achieve a well-designed structure with a specific function, the uniform distribution of CNTs into the used matrix is a key issue. Here, it is shown that a hierarchical composite of single/double-walled CNTs interlinked with two-dimensional flakes can be constructed via in-situ CNT growth onto layered double hydroxide (LDH) flakes. Both the wall number and diameter of the CNTs and the composition of the flakes can be easily tuned by changing the proportion of the transition metal in the LDH flakes. Furthermore, a structure with continuously interlinked CNT layers alternating with lamellar flakes is obtained after compression. The hierarchical composite is demonstrated to be an excellent filler for strong polyimide films. This study indicates that LDH is an extraordinary catalyst for the fabrication of hierarchical composites with high-quality single/double-walled CNTs. The as-obtained CNTs/calcined LDHs nanocomposite is a novel structural platform for the design of mechanically robust materials, catalysts, ion-transportation, energy-conversion, and other applications.

The growth of carbon nanotubes (CNTs) on natural materials is a low-cost, environmentally benign, and materials-saving method for the large-scale production of CNTs. Directly building 3D CNT architectures on natural materials is a key issue for obtaining advanced materials with high added value. We report the fabrication of aligned CNT arrays on fibrous natural wollastonite. Strongly dispersed iron particles with small sizes were produced on a planar surface of soaked fibrous wollastonite by a reduction process. These particles then catalyzed the decomposition of ethylene, leading to the synchronous growth of CNTs to form leaf- and brush-like wollastonite/CNT hybrids. The as-obtained hybrids could be further transformed into porous SiO₂/CNT hybrids by reaction with hydrochloric acid. Further treatment with hydrofluoric acid resulted in aligned CNT arrays, with purities as high as 98.7 %. The presented work is very promising for the fabrication of advanced materials with unique structures and properties that can be used as fillers, catalyst supports, or energy-absorbing materials.

Nanocomposites of interpenetrating carbon nanotubes and vanadium pentoxide (V₂O₅) nanowires networks are synthesized via a simple in situ hydrothermal process. These fibrous nanocomposites are hierarchically porous with high surface area and good electric conductivity, which makes them excellent material candidates for supercapacitors with high energy density and power density. Nanocomposites with a capacitance up to 440 and 200 F g⁻¹ are achieved at current densities of 0.25 and 10 A g⁻¹, respectively. Asymmetric devices based on these nanocomposites and aqueous electrolyte exhibit an excellent charge/discharge capability, and high energy densities of 16 W h kg⁻¹ at a power density of 75 W kg⁻¹ and 5.5 W h kg⁻¹ at a high power density of 3 750 W kg⁻¹. This performance is a significant improvement over current electrochemical capacitors and is highly competetive with Ni–MH batteries. This work provides a new platform for high-density electrical-energy storage for electric vehicles and other applications.