| Carbon nanotubes (CNTs) are a new type of one-dimensional functional materials, and their structure is similar to the graphite lamellar structure, which brings about excellent electrical properties. CNTs arrays can be directly grown on substrates by chemical vapor deposition (CVD) method, having advantages of simple operation, low cost, and controllable diameter size. Aligned carbon nanotube arrays have a huge potential advantage in the field of lithium-air batteries, and are expected to increase the energy density of the batteries. However, non-conductive substrates are often used for the growth of CNTs arrays, limiting their direct application in the electrochemical field. Therefore, CVD method was adopted and aligned CNTs arrays were prepared on quartz and electrically conductive carbon paper, characterized by SEM. Furthermore, the impact of process parameters on the morphology of the CNTs was investigated. The main results are as follows.1. Synthesis of CNTs arrays on quartz substratesHighly directional and well graphitized CNTs arrays were successfully fabricated on quartz substrate by floating catalyst CVD method, and the influence of process parameters on the morphology and deposit amount of CNTs, such as reaction temperature, the mole ratio of ferrocene and xylene, the reaction mixture gas linear velocity and the ratio of carrier gas (Ar/H2), was investigated. An optimum condition for the growth of CNTs arrays on quartz substrate was given as follows:reaction temperature was750℃, the mole ratio of ferrocene and xylene was1/75, the reaction mixture gas linear velocity was1.35cm/s, the ratio of carrier gas (Ar/H2) was7/1and H2flow rate was200sccm. The CNTs arrays obtained at the best conditions had a high graphitization degree. Besides, reaction temperature and the mole ratio of ferrocene and xylene had an important influence on the formation of CNTs arrays. Appropriate to reduce the reaction mixture gas linear velocity could reduce the generation of impurities, optimizing the microstructure of CNTs arrays, and the diameter and deposit amount of CNTs appeared decreased with H2flow rate increased.2. Synthesis of CNTs arrays on electrically conductive carbon paperPretreatment of carbon paper had an extremely important impact on growth of CNTs arrays by CVD method. First a thin film layer of the catalyst and the carbon black was coated on carbon paper as the gas diffusion layer of air electrode, and then good directional arrays of CNTs was successfully synthesized by CVD method. And the influence of process parameters on the morphology and deposit amount of CNTs, such as reaction temperature, the mole ratio of ferrocene and xylene, the reaction mixture gas linear velocity and the mole ratio of ethanol and xylene, was investigated.1) With the temperature increased, the deposit amount of CNTs arrays was presented first increased and then decreased, and the optimum temperature was800℃.2) When the reaction mixture gas linear velocity was too low, the diameter of CNTs was small and difficult to maintain directional; while linear velocity was too high, the growth of single nanotube became bent, more wall defects appeared and the amount of impurities increased. The best reaction mixture gas linear velocity was1.40cm/s.3) Catalyst had a direct impact on the morphology and structure of CNTs. Too low mole ratio of ferrocene and xylene was not conducive to the continuous growth of CNTs, leading to a shorter length; when the mole ratio of ferrocene and xylene was too large, wall defects of CNTs generated, CNTs diameter more different, which was not conducive to the growth of CNTs arrays. The best mole ratio of ferrocene and xylene was1/30.4) The right amount of ethanol added to xylene could play a protective role on the surface of the catalyst particles and substantially increase the growth rate of CNTs arrays, and CNTs arrays had a high graphitization degree.5) The growth of CNTs arrays on carbon layer/carbon paper was based on top-growth pattern. |
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