A review of carbon nanotubes in modern electrochemical energy storage

The quest for sustainable energy storage solutions is more critical than ever,with the rise in global energy demand and the urgency of transition from fossil fuels to renewable sources.Carbon nanotubes(CNTs),with their exceptional electrical conduct-ivity and structural integrity,are at the forefront of this endeavor,offering promising ways for the advance of electrochemical energy storage(EES)devices.This review provides an analysis of the synthesis,properties,and applications of CNTs in the context of EES.We explore the evolution of CNT synthesis methods,including arc discharge,laser ablation,and chemical vapor deposition,and highlight the recent developments in metal-organic framework-derived CNTs and a novel CNT aggregate with a three-dimensional ordered macroporous structure.We also examine the role of CNTs in improving the performance of various EES devices such as lith-ium-ion,lithium-metal,lithium-sulfur,sodium,and flexible batteries as well as supercapacitors.We underscore the challenges that remain,including the scalability of CNT synthesis and the integration of CNTs in electrode materials,and propose potential solu-tions and future research directions.The review presents a forward-looking perspective on the pivotal role of CNTs in shaping the fu-ture of sustainable EES technologies.

In-situ homogeneous synthesis of carbon nanotubes on aluminum matrix and properties of their composites

Using nickel catalyst supported on aluminum powders, carbon nanotubes （CNTs） were successfully synthesized in aluminum powders by in-situ chemical vapor deposition at 650 ℃. Structural characterization revealed that the as-grown CNTs possessed higher graphitization degree and straight graphite shell. By this approach, more homogeneous dispersion of CNTs in aluminum powders was achieved compared with the traditional mechanical mixture methods. Using the in-situ synthesized CNTs/Al composite powders and powder metallurgy process, CNTs/Al bulk composites were prepared. Performance testing showed that the mechanical properties and dimensional stability of the composites were improved obviously, which was attributed to the superior dispersion of CNTs in aluminum matrix and the strong interfacial bonding between CNTs and matrix.

Composition Dependent Magnetic Properties of Ni-Co-P Coated Carbon Nanotubes

Carbon nanotubes were coated with a layer of nickel-cobalt-phosphorus （Ni-Co-P） alloy with different compositions of Ni/Co through electroless plating. The effects of the concentration ratio of Co^2＋ to Ni^2＋, bath temperature, and pH on deposition rate are discussed. The prepared carbon nanotubes covered with Ni-Co-P were characterized and analyzed by fieldemission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, energy dispersive spectroscopy, and a vibrating sample magnetometer. The results show that the deposition rate reached the maximum when the concentration ratio of Co^2＋ to Ni^2＋ is 1 and the pH is 9; the deposition rate increases with the increase of bath temperature. The measurements of the magnetic properties of the obtained carbon nanotubes covered with Ni-Co-P indicate that the magnetic properties greatly depend on the concentration ratio of Co^2＋ to Ni^2＋, and the magnetic saturation reaches the maximum value when the Co^2＋ to Ni^2＋ ratio is 1. In addition, there are two peaks in the coercivity curve at Co^2＋ to Ni^2＋ ratios of 1/2 and 4/1, while the two peaks in the magnetic conductivity curve are located at Co^2＋ to Ni^2＋ ratios of 1/4 and 4/1.

Study on the Mechanical Properties of Carbon Nanotube/Polyacrylonitrile Composite Fibers

The method of preparing the multi-walled carbon nanotubes (MWNTs)-polyacrylonitriIe (PAN) composite fibers is described and the effects of draw ratio on the mechanical properties of CNT/PAN fibers have also been discussed. The results show that the degrees of MWNTs dispersion in the polymer matrix have much effect on the mechanical properties.

Synthesis of aligned carbon nanotube with straight-chained alkanes by nebulization method

Aligned carbon nanotubes(CNTs)were synthesized by nebulized spray pyrolysis of solutions of organometallics in carbon precursor solvents.Four types of straight-chained alkanes including n-pentane,n-hexane,n-heptane and n-octane were used as precursor solvents for synthesis of aligned CNTs.The results from scanning electron microscopy,transmission electron microscopy and Raman spectroscopy show that the CNTs obtained from them have different diameters and degrees of graphitization. It is found that the n-heptane is the most suitable for the growth of aligned CNTs with high quality and yield.The thermodynamic properties of precursory carbon sources such as boiling point and formation enthalpy are considered to play a decisive role in the synthesis of CNTs.It will be very helpful for the controllable preparation of aligned CNTs at relatively low cost.

一氧化碳加氢制碳氢化合物反应选择性的调控

合成气(即一氧化碳加氢)催化转化制碳氢化合物的费托合成反应是煤、甲烷和生物质等非油基碳资源间接转化制液体燃料或化学品的关键步骤.在传统的费托合成催化剂上,产物服从Anderson-Schulz-Flory分布,特定产物的选择性差.设计和制备高选择性费托合成催化剂,实现C–C偶联产物选择性的调控,是现代C1化学最具挑战性的课题.本文概述了近年来有关C–C偶联机理方面的理论研究进展,简要总结了影响费托合成产物选择性的几个关键因素,着重阐述了活性金属尺寸及所处微环境对产物选择性和催化活性的影响.本文还评述了既具有一氧化碳加氢制高碳烃又具有高碳烃加氢裂解能力的双功能费托合成催化剂体系,并提出通过控制加氢裂解等二次反应控制费托合成产物选择性的新策略.

Templated synthesis of Ti02 nanotube macrostructures and their photocatalytic properties

Controlled synthesis of hierarchically assembled titanium dioxide （TiO2） nano- structures is important for practical applications in environmental purification and solar energy conversion. We present here the fabrication of interconnected TiO2 nanotubes as a macroscopic bulk material by using a porous carbon nanotube （CNT） sponge as a template. The basic idea is to uniformly coat an amorphous titania layer onto the CNT surface by the infiltration of a TiO2 precursor into the sponge followed by a subsequent hydrolysis process. After calcination, the CNTs are completely removed and the titania is simultaneously crystallized, which results in a porous macrostructure composed of interconnected anatase TiO2 nanotubes. The TiO2 nanotube macrostructures show comparable photocatalytic activities to commercial products （AEROXIDE TiO2 P25） for the degradation of rhodamine B （RhB）. Moreover, the TiO2 nanotube macrostructures can be settled and separated from water within 12 h after photocatalysis, whereas P25 remains suspended in solution after weeks. Thus the TiO2 nanotube macrostructures offer the advantage of easy catalyst separation and recycle and can be a promising candidate for wastewater treatment.

Understanding the discrepancy between the quality and yield in the synthesis of carbon nanotubes

High-quality carbon nanotubes （CNTs） are promising materials in many applications. However, current chemical vapor deposition （CVD） methods for CNT synthesis suffer from the discrepancy between the quality and yield of CNTs： Low-quality CNTs can be synthesized with high yield, while high-quality CNTs can only be synthesized with low yield. Here a CVD method has been designed to synthesize both high-quality and low-quality CNTs using the same combination of catalyst and precursor. As a result, we were able to understand the reasons for the low yield in high-quality CNT synthesis and a method was derived to improve their yield. This understanding is an important step towards high- yield synthesis of high-quality CNTs.

Effect of catalyst confinement and pore size on Fischer-Tropsch synthesis over cobalt supported on carbon nanotubes

This paper studies the impact of structure of cobalt catalysts supported on carbon nanotubes(CNT) on the activity and product selectivity of Fischer-Tropsch synthesis(FTS) reaction.Three types of CNT with average pore sizes of 5,11,and 17 nm were used as the supports.The catalysts were prepared by selectively impregnating cobalt nanoparticles either inside or outside CNT.The TPR results indicated that the catalyst with Co particles inside CNT was easier to be reduced than those outside CNT,and the reducibility of cobalt oxide particles inside the CNT decreased with the cobalt oxide particle size increasing.The activity of the catalyst with Co inside CNT was higher than that of catalysts with Co particles outside CNT.Smaller CNT pore size also appears to enhance the catalyst reduction and FTS activity due to the little interaction between cobalt oxide with carbon and the enhanced electron shift on the non-planar carbon tube surface.

One-step preparation of novel conjugated porous polymer with tubular structure

A shape-persistent dendritic molecule,tris(4-(2,7-dibromo-9-phenyl-9-fluoren-9-yl)phenyl)amine (TF-6Br),has been readily synthesized in high yield through a concise Friedel-Crafts reaction from triphenylamine and 2,7-dibromo(9-phenyl-fluoren-9-ol).It was further employed as the key building block to achieve the synthesis of conjugated porous polymer via Sonogashira coupling with 1,4-diethynylbenzene.Under experimental reaction conditions,the resulting porous polymer shows exceptionally nanotubular morphology,which further allows for a template-free synthesis of porous carbon nanotubes via thermal treatment at high temperature.The obtained nitrogen-doped carbon nanotubes feature with an improved porosity and high surface area.

Freestanding macroscopic metal-oxide nanotube films derived from carbon nanotube film templates

Aligned carbon nanotube films coated with amorphous carbon were developed into novel templates by atomic layer deposition. Freestanding macroscopic metal-oxide nanotube films were then successfully synthesized by using these templates. The reactive amorphous carbon layer greatly improved the nuclei density, which ensured the high quality of the films and allowed for precise control of the wall thickness of the nanotubes. Using template-synthesized alumina nanotube films, we demonstrate a humidity sensor with a high response speed, a transmission electron microscopy （TEM） grid, and a catalyst support. The cross- stacked assembly, ultrathin thickness, chemical inertness, and high thermal stability of the alumina nanotube films contributed to the excellent performance of these devices. In addition, it is expected that the metal-oxide nanotube films would have significant potential owing to their material richness, macroscopic appearance, flexibility, compatibility with the semiconducting technologies, and the feasibility of mass production.

Synthesis and TEM structural characterization of C60-flattened carbon nanotube nanopeapods

A fully flattened carbon nanotube （FNT）, a graphene nanoribbon （GNR） analogue, provides a hollow space at edges for endohedral doping. Due to the unique shape of the hollow space of FNTs, novel types of low-dimensional arrangements of atoms and molecules can be obtained through endohedral doping into FNTs, which provides a new type of nanopeapods. FNT-based nanopeapods have been synthesized through endohedral doping of C60, and their structural characterization with transmission electron microscopy （TEM） performed. The doping of C60 into the inner hollow space of FNTs has been carried out via the gas-phase filling method, where open-ended FNTs are sealed in a glass ampoule and heated at 723-773 K for two days. TEM observations show that most of the encapsulated C60 molecules align as single molecular chains along the edges of FNTs and that some of the C60 forms two-dimensional close-packed structures inside FNTs.