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首页> 外文期刊>Crystal growth & design >Zebra-striped fibers in relation to the H _2 sorption properties for MgH _2 nanofibers produced by a vapor-solid process
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Zebra-striped fibers in relation to the H _2 sorption properties for MgH _2 nanofibers produced by a vapor-solid process

机译：斑马条纹纤维与通过气固法制备的MgH _2纳米纤维的H _2吸附性能

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摘要

MgH 2 is a promising candidate for solid-state H _2 storage applications. To improve the H _2 sorption kinetics, highly pure MgH _2 nanofibers were synthesized by a vapor-solid process. The fibers showed improved sorption kinetics compared with bulk MgH _2, which were investigated by a volumetric pressure-composition-temperature method. To choose a meaningful kinetic model that represented the physical reality and intrinsic kinetic parameters for the unique fiber structure, theoretical modeling of the sorption data and metallographic examinations of the in situ dehydrogenation process and partially hydrogenated samples were carried out. The Johnson-Mehl-Avrami (JMA) model, which is based on the theory of nucleation and growth transformation, was selected for the kinetic mechanism analysis of the hydrogenation/dehydrogenation of the fibers. The theoretical modeling by the JMA model indicated that the phase transformation of Mg to MgH _2 (or of MgH _2 to Mg) in the individual fibers proceeded one-dimensionally along the zebra-striped MgH _2-Mg interfaces in the longitudinal direction of the fibers, as confirmed by the observation of the in situ dehydrogenation process and the partially hydrogenated samples. Interestingly, during the H _2 absorption/desorption steps, the fibers were separated into periodic white-black (MgH _2-Mg) zebra stripes, and the phase growth proceeded along the white-black interfaces in the longitudinal direction of the fibers. The activation energies for hydrogenation and dehydrogenation were estimated to be 116.55 and 150.78 kJ/mol, respectively, which were within the range of previously reported values for bulk MgH _2.
机译：MgH 2是固态H _2存储应用的有希望的候选者。为了提高H _2的吸附动力学，通过气固法合成了高纯度的MgH _2纳米纤维。与体积MgH _2相比，该纤维表现出改善的吸附动力学，这是通过体积压力-组成-温度方法研究的。为了选择一个有意义的动力学模型，该物理模型代表独特的纤维结构的物理事实和内在动力学参数，对吸附数据进行了理论建模，并对原位脱氢过程和部分氢化的样品进行了金相检查。选择基于成核和生长转化理论的Johnson-Mehl-Avrami（JMA）模型进行纤维加氢/脱氢的动力学机理分析。 JMA模型的理论建模表明，单个纤维中Mg到MgH _2（或MgH _2到Mg）的相变是沿着斑马条纹MgH _2-Mg界面在纤维的纵向上一维进行的。如通过原位脱氢过程和部分氢化样品的观察所证实。有趣的是，在H _2吸收/解吸步骤中，纤维被分成周期性的白黑（MgH _2-Mg）斑马条纹，并且相的生长沿纤维的纵向沿着白黑界面进行。估计氢化和脱氢的活化能分别为116.55和150.78 kJ / mol，这在先前报道的MgH _2值的范围内。

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