新型轻金属（Li，Mg，Al）固溶体材料储氢及机理研究

Hydrogen storage is the main carrier of hydrogen energy. Although showing high hydrogen storage capacities for LiH, MgH2 and AlH3, these hydrides can not be used for hydrogen storage materials directly due to poor properties of hydrogenation/dehydrogenation thermodynamics and kinetics. .Based on the thermodynamic theory of solid solution, a comprehensive research program for (Li, Mg, Al) metastable solid solution applied to hydrogen storage is proposed in this project. Extensive and systematic experimental studies will be carried out to explore the preparation of the (Li, Mg, Al) solid solution hydrogen storage materials with high hydrogen storage capacity, good thermodynamic and kinetic properties. The process for adjusting alloy microstructures and the influence of alloy microstructures on hydrogen storage properties will be investigated. The interaction between hydrogen and alloy is a significant factor influencing the property of alloy hydrogenation/dehydrogenation, the addition of catalyst can improve the property. So the choice of catalyst will also be necessary. .In order to characterize the alloy microstructure some analysis methods will be used. For example, XRD and TEM will be applied to the change of alloy microstructure during hydrogenation/dehydrogenation and the correlation between microstrucure and hydrogen storage property, thermo analysis be used to the study on thermodynamics and kinetics of alloy hydrogenation/dehydrogenation, and NMR analysis be used to verify the effect of catalyst on hydrogen bonding action, XPS analysis also be employed to explore the electronic state of alloy surface and the interaction between hydrogen and alloy during hydrogenation/dehydrogenation..The first principle density function calculation will be applied to the structural stabilities of solid solution and hydride, the behaviour of hydrogen in hydride and the characteristic of electronic structure. Furthermore, the interaction between hydrogen and solid solution, the hydrogen storage mechanism will be investigated. .The project will provide theoretic basis for designing and preparing novel hydrogen storage materials.

氢存储是氢能的主要载体，LiH、MgH2、AlH3储氢量较高，但氢化/脱氢热力学和动力学性能差，不能直接用作储氢材料。本项目根据固溶体热力学理论，提出一种以（Li，Mg，Al）亚稳态固溶体储氢方法，探索制备具有高储氢量、热力学和动力学性能良好的（Li，Mg，Al）固溶体储氢材料，探索调控组织结构的工艺条件、组织结构对储氢性能的影响机制，研究提高吸放氢热力学、动力学性能催化剂的选取。利用XRD、TEM等研究氢化前后组织结构的变化及与储氢性能的相关性，通过热分析研究合金氢化、脱氢的热力学和动力学，利用NMR研究催化对氢成键作用的影响，对合金氢化前后进行光电子能谱等分析，研究合金表面电子态以及氢与合金作用方式。通过第一原理理论计算，研究固溶体及氢化物结构稳定性、氢化物中氢的行为以及电子结构特征，揭示氢与固溶体合金相互作用关系及储氢机制，为制备新一代储氢材料提供理论依据。

氢存储是氢能的主要载体，LiH、MgH2、AlH3储氢量较高，但氢化/脱氢热力学和动力学性能差，不能直接用作储氢材料。本项目根据固溶体热力学理论，提出一种以（Li，Mg，Al）亚稳态固溶体储氢方法，并研究其储氢性能。. 采用烧结球磨的方法制备Mg17Al12合金，并研究不同的冷却方法对Mg17Al12合金的储氢性能影响具有相同Mg17Al12相的合金，经过不同的制备方法处理后会表现出不同的氢化反应。例如，当合金经烧结并在液氮温度下冷却的氢化反应为：Mg17Al12+H2Mg2Al3+ MgH2+Al；当样品再经70小时球磨，其可逆氢化反应为：Mg17Al12+H2 MgH2+Al，最大储氢量达到4.0wt.%，接近理论值4.4 wt%。所以，球磨不仅仅能提高样品的储氢量，还能降低样品的放氢温度，提高放氢速率。液氮温度下的非平衡快速冷却过程明显改善Mg17Al12合金的氢化反应动力学性能。综上所述，液氮温度下的非平衡快速冷却过程与球磨共同作用能有效降低氢化反应的激活能，同时能够调控Mg17Al12合金的氢化过程和储氢性能。. 通过烧结和球磨制备Mg-Li固溶体并探究其储氢特性。XRD数据分析表明，Mg-Li固溶体在氢化反应中是可逆的： 。而且随着合金中Si的添加，有Mg2Si相形成。Mg2Si相作为催化剂提升了Mg-Li固溶体的吸放氢性能。例如，以2K/min升温速率从室温加热至650K，Mg90Li4Si6(x=6)合金完全放氢，而Mg90Li10(x=0)合金在相同条件下只能释放吸氢量的28.6%。而与Mg90Li10 (x=0)合金相比，Mg90Li4Si6(x=6)合金的初始放氢温度明显降低。此外，Mg90Li4Si6(x=6)合金的表观活化能（Ea）为128.3 kJmol-1，比Mg90Li10(x=0)合金低51.2 kJmol-1。Mg2Si作为催化剂降低了Mg-Li固溶体吸放氢过程反应势垒。. 基于密度泛函理论方法，研究了氢在Mg17Al12 (100)表面吸附、解离以及氢在表面体内扩散的过程。氢分子在表面发生解离吸附需要跨越最小约为0.63 eV的势垒。氢与表面的作用主要是氢原子的s轨道和镁原子的s 轨道之间的杂化。氢原子吸附使得最外层表面近邻镁原子间的键长从4.48 Å 缩短到3.30 Å，显示了镁氢原子间的较强的相互作用。