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The combination of nanomaterials with complementary properties in a well-designed architecture is an attractive strategy to develop multi-functional, high-performance materials for applications in energy conversion and storage, catalysis, electronic devices, and more. Herein, we propose three different methods: alternating filtration, spray coating, and in-situ wet chemistry synthesis, to achieve the hybridization of two-dimensional (2D) Ti 3 C 2 T x MXene and transition metal oxides (TMOs), such as Co 3 O 4 and NiCo 2 O 4 . The resulting flexible free-standing hybrid films were free of binders, conductive additives, or current collectors. When used directly as anodes for Li-ion batteries, these hybrid films successfully combined the metallic conductivity of Ti 3 C 2 T x and high capacity of TMOs, showing excellent electrochemical performance for Li-ion storage. High reversible capacities over 1200 mA h g −1 were achieved by the MXene/TMO hybrid film electrodes fabricated by all three methods. All films also exhibited impressive long cycling stabilities and excellent rate performances. In particular, the spray-coated Ti 3 C 2 T x /NiCo 2 O 4 hybrid film electrode achieved high reversible capacities of 1330, and 650 and 350 mA h g −1 at 0.1, 5 and 10 C, respectively, along with no capacity decay over hundreds of cycles. This work demonstrates that the hybridization of MXenes, a large family of 2D transition metal carbides/nitrides, and TMOs has a significant potential for energy storage, and is promising for expansion into other applications. [ABSTRACT FROM AUTHOR]

The global availability of sodium and a possibility to avoid the use of copper current collectors make electrochemical sodium-ion storage attractive for battery and metal-ion capacitor applications. However, the use of Na instead of Li ions requires different electrode materials that can accommodate larger Na ions and still provide high charging rate and high volumetric capacity. Herein we report on the fabrication of porous Ti 3 C 2 MXene/CNT composite paper electrodes for sodium-based energy storage devices. The heterostructure formation was realized by electrostatic attraction between negatively charged 2D MXene nanosheets and positively charged 1D CNTs. This method efficiently prevented restacking of MXene nanosheets and produced a well-defined porous structure, thereby facilitating electrolyte transport and access of ions to the electrode and producing functional MXene-based electrodes for sodium-ion storage. When applied as freestanding electrodes for sodium-ion storage, the built-to-order Ti 3 C 2 MXene/CNTs porous films showed high volumetric capacity of 421 mA h cm −3 at 20 mA g −1 , good rate performances, and excellent cycling stability. Prototype sodium-ion cells were also assembled using the as-prepared Ti 3 C 2 /CNTs anode and Na 0.44 MnO 2 cathode. The fabrication of porous MXene/CNT composites, using simple self-assembly, opens the door to developing electrode materials with high volumetric capacity for sodium-ion storage. [ABSTRACT FROM AUTHOR]

Abstract: The use of conductive carbon scaffolds is efficient and effective to obtain advanced composite cathodes for lithium–sulfur batteries. However, the loading amount of mostly less than 70 wt% induces a limited energy density and the typical fabrication route involving high-temperature and elaborate process also limits the manufacturability of sulfur cathode, both of which hinder the practical application of lithium–sulfur batteries. Herein, a scalable, room-temperature, and one-step method is employed for carbon nanotube (CNT)/sulfur composite cathode, in which aligned CNTs served as interconnected conductive scaffolds to accommodate sulfur. When the loading amount of sulfur increased from 50 to 90wt%, the tap density of CNT/sulfur increased from 0.4 to 1.98gcm−3, and the mass/areal/volumetric capacities of the whole electrodes (CNT/sulfur composites and binders) was improved from 500.3mAhg−1/0.298 mAhcm−2/200.1mAhcm−3 to 563.7mAhg−1/0.893 mAhcm−2/1116.0mAhcm−3, respectively. The rise of sulfur content in the composite cathode renders a dramatic increase of the energy density of lithium–sulfur cells. The ultra-high loading amount of sulfur is attributed to the open, ordered, straight pore structure of aligned CNT scaffolds for the uniform distribution of fine sulfur particles. The robust sp2 carbon frameworks served as rapid pathways for electron transfer, and the large aspect ratio, good alignment, ordered packing of individual CNT in small bundles offer a low conductive percolation threshold. Consequently, the sulfur with a high loading content was efficiently utilized for a lithium–sulfur cell with a much improved energy density. [Copyright &y& Elsevier]

Abstract: A family of layered double hydroxides (LDHs) with varied Fe contents were employed as catalyst precursors for the controllable bulk growth of few-layer graphene/single-walled carbon nanotube (G/SWCNT) hybrids in a fluidized-bed reactor through chemical vapor deposition of methane at 950°C. All the G/SWCNT hybrids exhibited the morphology of SWCNTs interlinked with graphene layers. The purity, thermal stability, graphitization degree, specific surface area, and total pore volume of the G/SWCNT hybrids decreased with the increasing Fe contents in the LDH precursors. A high yield of 0.97gG/SWCNTs/gcat can be achieved by tuning the Fe content in the FeMgAl LDHs after a 15-min growth. After the removal of the as-calcined FeMgAl layered double oxide flakes, a high carbon purity of ca. 98.3% for G/SWCNT hybrids was achieved when the mole ratio of Fe–Al is 0.05:1. The size and density of Fe nanoparticles decorated in the as-obtained G/SWCNT hybrids depend largely on Fe content in the FeMgAl LDH precursors. Furthermore, the mass ratio of graphene materials to SWCNTs in the as-prepared G/SWCNT hybrids can be well controlled in a range of 0.4–15.1. [Copyright &y& Elsevier]

Abstract: CoMgAl layered double hydroxides were prepared as catalysts for the in situ synchronous growth of graphene and single-walled carbon nanotubes (SWCNTs) from methane by chemical vapor deposition. The as-calcined CoMgAl layered double oxide (LDO) flakes served as the template for the deposition of graphene, and Co nanoparticles (NPs) embedded on the LDOs catalyzed the growth of SWCNTs. After the removal of CoMgAl LDO flakes, graphene (G)/SWCNT/Co3O4 hybrids with SWCNTs directly grown on the surface of graphene and 27.3wt.% Co3O4 NPs encapsulated in graphene layers were available. Further removal of the Co3O4 NPs by a CO2-oxidation assistant purification method induced the formation of G/SWCNT hybrids with a high carbon purity of 98.4wt.% and a high specific surface area of 807.0m2/g. The G/SWCNT/Co3O4 hybrids exhibited good electrochemical performance for pseudo-capacitors due to their high Co3O4 concentration and the high electrical conductivity of SWCNTs and graphene. In another aspect, the G/SWCNT hybrids can be used as excellent electrode materials for double-layer capacitors. A high capacity of 98.5F/gelectrode was obtained at a scan rate of 10mV/s, 78.2% of which was retained even when the scan rate increased to 500mV/s. [Copyright &y& Elsevier]

Abstract: The Li–S battery is with a much greater theoretical energy density than those of conventional lithium ion batteries. The key to achieve a high performance electrode for Li–S battery lies in the arrangement of the building blocks into a well-designed structure, in which the nanocarbon framework not only acts as an electronic conduit to the encapsulated active materials but also serves as a mini-electrochemical reaction chamber. Therefore, a nanocomposite with sulfur entrapped into hierarchical porous graphene was proposed and fabricated for Li–S batteries. The nanocomposite electrode exhibits high discharging capacitance of 1068 and 543mAhg−1 at a current density of 0.5 and 10C, respectively. The discharging capacity of 386mAhg−1 can be presented at ultra-low temperature of −40°C, which far exceeds the operating range of conventional lithium-ion batteries. The large scale produced hierarchal graphene was mainly decorated with epoxy and hydroxyl groups, which can enhance the binding of S to the C–C bonds due to the induced ripples by the functional groups. These results provided a promising electrode material for energy storage device with high capacitance, which is important for the increasing demands of power sources in cold environments, such as battery systems for electric vehicles in cold zone or for aeronautic applications. [Copyright &y& Elsevier]

Abstract: Self-organization of nitrogen-doped carbon nanotube (N-CNT) double helices was achieved by chemical vapor deposition (CVD) with Fe–Mg–Al layered double hydroxides (LDHs) as the catalyst precursor. The as-obtained N-CNT double helix exhibited a closely packed nanostructure with a catalyst flake on the tip, which connected the two CNT strands on both sides of the flake. A mechanism for the self-organization of N-CNTs into double-helix structures with a moving catalyst head is proposed. Effective carbon/nitrogen sources, high-density active catalyst nanoparticles, space confinement, and the precise chiral match between the two CNT strands are found to be crucial for the N-CNT double helix formation. The morphologies of N-CNTs can be well tuned between bamboo-like and cup-stacked structures, and a CNT/N-CNT heterojunction can be constructed by changing the carbon feedstock from C2H4 to CH3CN during CVD growth. N-CNT double helices with a length of 10–36μm, a screw pitch of 1–2μm, a CNT diameter of 6–10nm, and a N-content of 2.59at.% can be synthesized on the LDH catalysts by the efficient CVD growth. [Copyright &y& Elsevier]

Abstract: Single-walled carbon nanotube (SWCNT) double helices were fabricated with directly synthesized FeMoMgAl layered double hydroxide flakes as the catalyst precursor. The as-obtained SWCNT double helices were closely packed, while the screw pitches of the double helices were tunable from 2 to 10μm. Straight millimeter-length SWCNT yarns can be obtained by further stretching the SWCNT double helices. [Copyright &y& Elsevier]

Abstract: A family of layered double hydroxides (LDHs), such as Fe/Mg/Al, Co/Mg/Al, and Ni/Mg/Al LDHs, were used as catalysts for the efficient growth of single-walled carbon nanotubes (SWCNTs) in a fluidized bed reactor. The LDH flakes were agglomerated into clusters with sizes ranging from 50 to 200μm, and they can be easily fluidized with a gas velocity ranging from 2.3 to 24cm/s. After calcination and reduction, small metal catalyst particles formed and distributed uniformly on the flakes. At the reaction temperature, the introduction of methane realized the growth of SWCNTs with the diameter of 1–4nm. The loose structure of LDH agglomerates afforded a yield as high as 0.95gCNT/(gcat h) of SWCNTs with a surface area of 930m2/g. Compared with Fe/Mg/Al LDH, Ni/Mg/Al and Co/Mg/Al LDHs showed a better selectivity to SWCNTs. The highest selectivity for metallic SWCNTs was obtained using Co/Mg/AI LDHs as the catalyst. [Copyright &y& Elsevier]

Abstract: A parametric study investigating the impacts of loading amount of active phase, growth temperature, H2 reduction, space velocity, and apparent gas velocity on the intercalated growth of vertically aligned carbon nanotube (CNT) arrays among lamellar catalyst was performed. A series of Fe/Mo/vermiculite catalysts with Fe/vermiculite ratio of 0.0075–0.300 were tested. Metal particles were dispersed among the layers of vermiculite after H2 reduction. Uniform catalyst particles, with a size of 10–20nm and a density of 8.5×1014 m−2, were formed among the vermiculite layers at 650°C. CNTs with high density synchronously grew into arrays among the vermiculites. With the increasing growth temperature, the alignment of CNTs intercalated among vermiculites became worse. Moreover, intercalated CNTs were synthesized among vermiculite layers in various flow regimes. The as-grown particles were with a size of 1–2mm when the fluidized bed reactor was operated in particulate fluidization and bubbling fluidization, while the size of the as-grown products decreased obviously when they grown in the turbulent fluidized bed. Based on the understanding of the various parameters investigated, 3.0kg/h of CNT arrays were mass produced in a pilot plant fluidized bed reactor. [Copyright &y& Elsevier]

Abstract: Vertically aligned carbon nanotube (CNT) arrays with ordered nanostructure and extraordinary performance have become an important advanced material. CNTs were synchronously grown with high density to form aligned morphology, while the fine agglomerated structure was sensitive to the packing style of catalyst particles. Thus, synthesis of CNT arrays in a fixed bed or fluidized bed is an important issue. We reported that CNT arrays were grown from ethylene on a lamellar catalyst in a fixed bed reactor and a fluidized bed reactor, respectively. The reactor style affected the intercalated growth of CNT arrays greatly. The qualities of CNT array products in the fixed bed showed a distribution along the axis direction. The CNT arrays obtained at the top of the fixed bed were of good alignment and small diameter; while for the products obtained at the bottom of the reactor, CNT array blocks with higher densities, larger diameter, shorter length, and more defects, were formed. When CNT arrays were grown in a fluidized bed, they were of homogeneous structure, low densities, small uniform diameter, and had little defects, which can be attributed to available space, uniform temperature and reactant distribution in the fluidized bed reactor. These favored the mass production of CNT arrays with uniform properties in a fluidized bed reactor. [Copyright &y& Elsevier]

Abstract: Large amount of vertically aligned carbon nanotube (CNT) arrays were grown among the layers of vermiculite in a fluidized bed reactor. The vermiculite, which was 100–300μm in diameter and merely 50–100μm thick, served as catalyst carrier. The Fe/Mo active phase was randomly distributed among the layers of vermiculite. The catalyst shows good fluidization characteristics, and can easily be fluidized in the reactor within a large range of gas velocities. When ethylene is used as carbon source, CNT arrays with a relatively uniform length and CNT diameter can be synthesized. The CNTs in the arrays are with an inner diameter of 3–6nm, an outer diameter of 7–12nm, and a length of up to several tens of micrometers. The as-grown CNTs possess good alignment and exhibit a purity of ca. 84%. Unlike CNT arrays grown on a plane or spherical substrate, the CNT arrays grown in the fluidized bed remain their particle morphologies with a size of 50–300μm and the good fluidization characteristics were preserved accordingly. [Copyright &y& Elsevier]

Abstract: Short aligned carbon nanotubes (CNTs) were intercalated grown among vermiculite layers from ethylene using a simple fluidized bed chemical vapor deposition (CVD) process. The length of CNTs ranged from 0.5 to 1.5μm after a synthesizing duration of 1–5min at 650°C. The as-grown CNTs vertically aligned to the vermiculite layers were with the mean outer and inner diameter of 6.7 and 3.7nm, respectively. A CNT yield of 0.22g/gcat was obtained for a 5-min growth. Those indicated that the fluidized bed CVD was an effective way for mass production of short CNTs. [Copyright &y& Elsevier]

The graphene/carbon nanotube (CNT) hybrids are considered as one of the most advanced nanostructures with intrinsically self-dispersion properties for large-volume applications. However, owing to the limited understanding on the complex growth mechanism and non-linear kinetics, rational design of growth procedures and related multiphase reactors for the production of the hybrids remain great challenges. In this contribution, the in-situ monitoring of graphene/CNT hybrid synthesis on layered double oxide bifunctional catalysts was carried out in an online thermogravimetric reactor. The rapid growth of CNTs occurred at the initial 90 s and the slow deposition of graphene was throughout the whole process, becoming the dominant reaction in the second stage. Based on this unique growth behavior, a two-stage growth strategy was proposed to improve the quality of hybrid products. The deposition of amorphous carbon byproduct was significantly suppressed and the quality of the hybrids was significantly enhanced through the two-stage growth process. [ABSTRACT FROM AUTHOR]

Abstract: Natural sepiolite mineral was used as a catalyst and catalyst support for the efficient growth of single-walled carbon nanotubes (SWCNTs). With the introduction of hydrogen, uniform active metal nanoparticles can be formed in the fibrous structure of sepiolite ore. High-quality SWCNTs with few defects and a large aspect ratio (over 104) were synthesized. The structure of the CNTs was modified by controlling the catalyst composition with ion-exchange method and changing the growth conditions. The 1 wt.% Fe-based catalyst exhibited excellent activity for the growth of SWCNTs, while the Co/Mo-based catalyst preferred to grow small diameter SWCNTs. The reaction temperature showed a sensitive selectivity to the chirality and diameter distribution of the SWCNTs produced. Catalysts based on the sepiolite can also afford the effective growth of SWCNTs in a fluidized bed reactor. As-grown SWCNTs/calcined-sepiolite demonstrated excellent ability of phenol adsorption, with an adsorption capacity of 155.8mg/g, which was much higher than that on natural sepiolite (12.7mg/g). [Copyright &y& Elsevier]

Abstract: A simple method is reported for the fast growth of millimeter-tall aligned carbon nanotubes (CNTs). Two silicon substrates were stacked with catalyst layers face to face and CNT growth occurred between them. Based on in situ monitoring, the growth rate of aligned CNTs in stacked area was found to be much (over one magnitude) higher than that in the area with a single substrate. The phenomenon was also valid for different catalyst layers and cap substrate materials. This provided an easy way to improve the efficiency of CNT synthesis without changing catalyst compositions and growth parameters. [ABSTRACT FROM AUTHOR]

Abstract: Free standing vertically-aligned carbon nanotube (CNT) arrays were released from a quartz substrate on a large scale by using CO2 as an oxidative reagent to weaken the array–substrate interaction and facilitate their harvest. During the oxidation process, amorphous carbon and carbon in contact with metallic particles were preferentially etched, leading to the easy release of high quality free standing CNT arrays. O2 was also used as an oxidant for comparison. The O2 showed a stronger oxidizability and caused the formation of CNTs with a turbostratic–graphitic carbon heterojunction structure. The mechanisms of CO2 and O2 oxidation of CNT arrays were investigated, and based on these results, CO2 was considered a more suitable oxidant for the purpose. [Copyright &y& Elsevier]

Abstract: Vertically aligned carbon nanotube (VACNT) arrays grown on ceramic spheres are obtained from ethylene using a floating catalysis process. The exhaust gas mainly contains light gaseous hydrocarbons, which decreases the contamination at the outlet of the reactor. Linear synchronous growth of the VACNT arrays is demonstrated and the morphology evolution of VACNT array grown on spheres is shown. The VACNT arrays on the spheres crack radially into a flower-like structure when the length of CNT is above 400μm. The VACNT arrays grown on spheres still possess good flowability even when the length of the array reaches 1100μm after a 2-h growth at 800°C. The arrays on the spheres show good alignment, high purity and good graphitization. Meanwhile, with a decrease in temperature, the diameter of CNTs in the array correspondingly decreases, the distribution becomes narrower, and the growth rate decreases. The apparent activation energy is 180±8kJ/mol, indicating that ethylene is a good carbon source for fast and continuous radial growth of millimeter VACNT arrays on ceramic spheres. [Copyright &y& Elsevier]

Introducing graphene protuberances covalently bonded with the graphene sheets is a straightforward strategy to avoid the stacking of graphene layers. The as-obtained unstacked double-layer templated graphene (DTG) is expected to fully demonstrate intrinsic properties of graphene assemblies if its detailed structure and component can be well controlled. Herein, both the lateral size and graphene protuberance size and areal density of DTG were well modulated through adjusting the template morphology and casting procedures. The lateral size of the as-obtained DTG was ranging from 0.4 to 2 μm. They exhibited a very high specific surface area ranging from 1336 to 1579 m 2 g −1 and tailorable graphene protuberances with areal density from 5.3 × 10 14 to 7.8 × 10 14 m −2 . DTG flakes with more hydrophilic surface and well tunable reactivity were obtained by introducing nitrogen into DTG through in-situ deposition. The as-synthesized N-doped DTG afforded significantly improved reactivity on oxygen reduction reaction (nearly 50 mV positively shifted onset potential compared with that of pristine DTG and a current preservation of 92.8% after 16,000 s test). [ABSTRACT FROM AUTHOR]

Abstract: Herringbone carbon nanofibers (CNFs) were efficiently produced by chemical vapor deposition on Ni nanoparticles derived from layered double hydroxide (LDH) precursors. The as-obtained CNFs with a diameter ranging from 40 to 60nm demonstrated herringbone morphologies when they grew on Ni/Al LDH derived catalysts both in the fixed-bed and fluidized-bed reactor. The Ni/Mg/Al, Ni/Cu/Al, as well as Ni/Mo/Mg/Al catalysts were also effective to grow herringbone CNFs. The diameter and specific surface area of the as-obtained CNFs highly depended on the catalyst composition and the growth temperature. When CNFs were grown at 550°C on Ni/Al catalyst, the as-obtained products had an outer diameter of ca. 50nm and a specific surface area of 242m2 g−1, possessed a discharge capacity of 330mAhg−1 as the electrode in a two-electrode coin-type cell. With the increase of the surface area, the discharge capacity increased at a rate of 0.90mAhcm−2, while the initial coulombic efficiency decreased gradually on nanocarbon anodes. This is attributed to the fact that CNFs with higher surface area afford smaller sp2 carbon layer that facilitated more Li ions to extract from the anodes. [Copyright &y& Elsevier]

Abstract: Fluffy carbon nanotubes (CNTs), which are cotton-like macroscopic structures, are obtained by simple high-speed shearing of vertically aligned CNT (VACNT) arrays. The fluffy CNTs are composed of CNT bundles with a diameter of several micrometers, and have an extremely low apparent density of 3–10g/L. A requisite for their formation is the alignment of CNTs in the initial array. The shear between the rotor and the arrays tears the arrays along the axial direction and this results in their dispersion into low density fluffy CNTs. [Copyright &y& Elsevier]