Mg基储氢材料释氢性能的掺杂效应及机理

发布时间：2018-03-10 08:45

  本文选题：Mg基储氢材料　切入点：释氢性能　出处：《湘潭大学》2015年硕士论文　论文类型：学位论文

【摘要】：Mg元素因其具有储氢量大(7.6wt%)、资源丰富、成本低等优点而被誉为是最具发展前景的金属储氢材料之一。而Mg基储氢材料要实现广泛应用,则必须很好地解决由氢在Mg表面难解离、难脱附所导致的吸、释氢速率缓慢的动力学问题和由其本身结构稳定性偏高所导致释氢温度偏高的热力学问题。目前,人们通过纳米结构调制、添加催化剂等方式已基本解决Mg基储氢材料吸、释氢速率缓慢的动力学问题,而释氢温度偏高的热力学问题仍是Mg基储氢材料走向实际应用所面临的难题。本论文以Mg基氢化物(MgH2)为研究对象,通过实验与理论计算相结合的方式,逐层深入研究了过渡金属与碳材料单独、复合掺杂对MgH2释氢性能的影响规律,着重分析了其掺杂改性机理。具体研究所得结论如下:(1)采用机械球磨的方法将过渡金属(Ti或Ni)单独掺杂以及复合掺杂于MgH2粉末中,结合理论计算研究表明:当Ni、Ti单独掺杂时,不仅能够改善MgH2体系的吸、释氢动力学性能,而且通过固溶的方式致使MgH2的晶格变形、结构稳定性降低,进而使体系初始释氢温度大幅度降低,其中,Ni的掺杂效果尤为明显,相对于纯MgH2降低了近136℃;而当Ni、Ti复合掺杂时,由于NiTi新相的生成使得体系合金表面张力增加,从而使体系颗粒细化效果较单独掺杂时并未提高,但复合掺杂体系的初始释氢温度较单独掺杂时却进一步降低,体系的初始释氢温度较纯MgH2降低了近161℃。(2)为缓解过渡金属掺杂致使MgH2体系储氢容量下降的问题,首先选择了本身具有物理储氢特性的碳材料(如Graphite、Graphene)作为掺杂物,研究了碳材料掺杂对MgH2释氢性能的影响及机理,研究表明:Graphite与Graphene掺杂,均对MgH2颗粒起到结构限域作用,使其颗粒细化且尺寸均匀,进而使MgH2体系初始释氢温度降低,其中Graphene的掺杂效果优于Graphite,相对于纯MgH2降低了近33℃;其掺杂机理在于碳材料的结构限域作用,削弱了MgH2中的Mg-H键,从而使其释氢温度降低。(3)基于(1)、(2)研究结果,选取掺杂效果优异的Ni与Graphene作为掺杂物,进一步研究了过渡金属与碳材料复合掺杂对MgH2释氢性能的影响及机理,研究表明:由于Graphene对MgH2颗粒的包覆缓冲作用,其掺杂顺序对MgH2体系释氢性能具有显著影响,即当Graphene与Ni同时掺杂时,体系初始释氢温度并未降低;而先掺杂Ni球磨4h、后掺杂Graphene球磨2h时,则使得MgH2体系的初始释氢温度较单独掺杂体系进一步降低,相对于纯MgH2体系而言,其初始释氢温度降低了近175℃,很好地实现了过渡金属与碳材料的协同掺杂效应。
[Abstract]:Mg element is regarded as one of the most promising metal hydrogen storage materials for its advantages of large hydrogen storage capacity, high hydrogen storage capacity, rich resources and low cost. However, if mg based hydrogen storage materials are to be widely used, it must be well resolved that hydrogen is difficult to dissociate from mg surface. The kinetics of the slow rate of hydrogen release and the thermodynamics of the high temperature of hydrogen release caused by the high stability of its own structure. At present, it is modulated by nanostructures. The kinetics of Mg-based hydrogen storage materials has been basically solved by adding catalysts, such as the slow rate of hydrogen release. However, the high temperature of hydrogen release is still a difficult problem in the practical application of Mg-based hydrogen storage materials. In this paper, the Mg-based hydride (MgH2) is taken as the research object, and the experimental results are combined with the theoretical calculation. The effects of transition metals and carbon materials on the hydrogen release properties of MgH2 were studied layer by layer. The mechanism of doping modification was emphatically analyzed. The conclusions are as follows: (1) the transition metal Ti or Ni) is doped by mechanical ball milling alone or by composite doping into MgH2 powder. The theoretical calculation results show that: when Niti is doped alone, It can not only improve the adsorption and hydrogen release kinetics of MgH2 system, but also deform the lattice of MgH2 by solid solution, decrease the stability of the structure, and decrease the initial hydrogen release temperature of the system, especially the doping effect of Ni. Compared with pure MgH2, the surface tension of the alloy is increased due to the formation of the new phase of NiTi, and the grain refinement effect of the system is not improved compared with that of the single doping, and the surface tension of the alloy is increased due to the formation of the new phase in the Niti Ti composite doping. However, the initial hydrogen release temperature of the composite doping system is further lower than that of the single doping system, and the initial hydrogen release temperature of the complex doping system is nearly 161 鈩，

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