Continuous flow chemical vapour deposition of carbon nanotube sea urchins

Solvothermal synthesis of hair-like carbon nanotubes onto sub-micron-sized spherical metal oxide catalyst cores

Long- and uniform-length, and high-density hair-like carbon nanotubes (CNTs) were produced by CNT growth on sub-micron-sized spherical catalyst supports. The nanosized catalysts (FeO _x , CoO _x , and NiO _x ) that were supported in/on the sub-micron-sized spherical metal oxides (TiO₂, ZrO₂, SnO₂, and CeO₂) were prepared via one-step solvothermal and/or two-step impregnation methods. The nanosized catalysts supported in/on the spherical metal oxide supports were converted into CNT conjugates with the CNT-hair morphology via a chemical thermal vapor deposition technique using ethyne gas as a carbon source; the CNTs grew on the central spherical metal oxide core under the base growth process conditions. Among the many types of candidate spherical catalyst materials, the combination of FeO _x as a catalyst for CNT growth and ZrO₂ as a support led to the best growth of CNT-hair under the reaction conditions, which included a temperature of 730 °C, pressure of 65 Pa, a 10 sccm ethyne gas flow, and a reaction time of 10 s. The CNTs consisted of five-to-eight-layered multi-wall structures with lengths of approximately 3 μm. The CNT-hair that was obtained using the solvothermally embedded catalyst showed higher crystallinity and was dense, thick, and straight, while the corresponding CNT-hair obtained using the impregnated catalyst was slightly sparse, thin, and curly. A unique layer structure constructed using large quantities of uniform CNT-hair, including multiple CNT yarns similar to fuzzy balls or cotton candies, was assembled. The CNT-hair conjugate, specifically constructed in a layer structure with core FeO _x /ZrO₂ catalysts and tangled CNT yarns, had an appearance similar to frog eggs. Therefore, we successfully prepared suitable catalysts for CNT-hair production and fabricated a layer structure consisting of large numbers of CNT-hair conjugates. The unique structures are expected as a new metamaterial with intriguing physical properties, including isotropic absorption of polarized light and electromagnetic waves.

Plasma production of nanomaterials for energy storage: continuous gas-phase synthesis of metal oxide CNT materials via a microwave plasma

In this work we show for the first time that a continuous plasma process can synthesize materials from bulk industrial powders to produce hierarchical structures for energy storage applications. The plasma production process's unique advantages are that it is fast, inexpensive, and scalable due to its high energy density that enables low-cost precursors. The synthesized hierarchical material is comprised of iron oxide and aluminum oxide aggregate particles and carbon nanotubes grown in situ from the iron particles. New aerosol-based methods were used for the first time on a battery material to characterize aggregate and primary particle morphologies, while showing good agreement with observations from TEM measurements. As an anode for lithium ion batteries, a reversible capacity of 870 mA h g-1 based on metal oxide mass was observed and the material showed good recovery from high rate cycling. The high rate of material synthesis (∼10 s residence time) enables this plasma hierarchical material synthesis platform to be optimized as a means for energetic material production for the global energy storage material supply chain.

Continuous-Flow Synthesis of Carbon-Coated Silicon/Iron Silicide Secondary Particles for Li-Ion Batteries

The development of better Li-ion battery (LIB) electrodes requires an orchestrated effort to improve the active materials as well as the electron and ion transport in the electrode. In this paper, iron silicide is studied as an anode material for LIBs because of its higher conductivity and lower volume expansion compared to pure Si particles. In addition, carbon nanotubes (CNTs) can be synthesized from the surface of iron-silicides using a continuous flow coating process where precursors are first spray dried into micrometer-scale secondary particles and are then flown through a chemical vapor deposition (CVD) reactor. Some CNTs are formed inside the secondary particles, which are important for short-range electrical transport and good utilization of the active material. Surface-bound CNTs on the secondary particles may help establish a long-range conductivity. We also observed that these spherical secondary particles allow for better electrode coating quality, cyclability, and rate performance than unstructured materials with the same composition. The developed electrodes retain a gravimetric capacity of 1150 mAh/g over 300 cycles at 1A/g as well as a 43% capacity retention at a rate of 5 C. Further, blended electrodes with graphite delivered a 539 mAh/g with high electrode density (∼1.6 g/cm³) and areal capacity (∼3.5 mAh/cm²) with stable cycling performance.

Facile growth of carbon nanotubes using microwave ovens: the emerging application of highly efficient domestic plasma reactors

The facile growth of carbon nanotubes (CNTs) using microwave radiation reveals a new way for the cost-effective synthesis of CNTs for a wide range of applications. In this regard, domestic microwave ovens can be used as convenient plasma reactors to grow CNTs in a very fast, simple, energy-saving and solvent-free manner. The special heating mechanism of microwaves can not only accomplish the fast growth of high-density CNT brushes within tens of seconds, but also eliminate the need for a flammable gaseous carbon source and an expensive furnace. By carefully selecting the substrate and catalyst, low-temperature growth of CNTs can also be achieved on low-melting point organic polymers at atmospheric pressure. Highly localized heating near the catalyst nanoparticles was observed under microwave irradiation, and this phenomenon can be utilized to grow CNTs at desired locations on the substrate to fabricate CNT-based nanoelectronics in situ. Finally, the microwave growth of CNTs is highly adaptive to different carbon sources, substrates and catalysts, showing enormous potential to generate functionalized CNT-based composites for emerging advanced applications.