具有层状堆垛亚结构的Ca-Mg-Ni三元化合物及其储氢特性

The ternary Ca-Mg-Ni compounds with layer-stacking substructure are promising materials for hydrogen storage. Based on our preliminary work, a systematic study on ternary Ca-Mg-Ni compounds and their hydrogen storage properties is proposed in this project. First ,the chemical compsition and crystal structure of each Ca-Mg-Ni compounds formed within the composition range of ABx(where x=3-4, A stands for Ca and Mg, and B for Ni) will be determined, with an emphasis on the identification of new stoichometric Ca-Mg-Ni compounds and their features in substructure. In order to reveal the relationshiop of composition-structure-property, the thermodynamic and kinetic data for hydrogen absorption/desorption will be measured thoroughly, as well as the cycling life and (sub-)strructural stability of the compounds. Finally, the Ca-Mg-Ni compounds with optimal hydrogen storage properties will be selected, including their crystal strucutre-type and stoichmetric proportion. The strategies for further improving their properties will be discussed and suggested. The outcomes yielded from this project may provide fundamental and valuable information for the development of new intermetallics for hyddrogen storage.

具有层状堆垛亚结构的Ca-Mg-Ni系化合物是一类有应用前景的新型储氢材料。在前期工作的基础上，申请人提出系统地研究Ca-Mg-Ni系的三元化合物及其储氢性能。首先，研究在ABx（A=Ca 、Mg, B=Ni, x=3-4）成分范围内，Ca-Mg-Ni系的相组成、相结构随成分的演变规律，重点分析具有新化学计量比的三元化合物及其结构和亚结构特征；其次，通过测试化合物的吸/放氢热力学和动力学的基础数据，研究在吸/放氢过程中化合物的循环寿命和晶体结构的稳定性，揭示化合物的储氢行为变化规律；最后，筛选出具有良好储氢性能的Ca-Mg-Ni化合物及晶体结构类型，并提出改善Ca-Mg-Ni系化合物储氢性能的途径。本项目的研究结果将为研发新型金属储氢材料提供理论依据。

以原子半径逐渐减小的稀土元素Nd (1.82 Å)、Gd (1.80 Å)和Er (1.76 Å)对Ca-Mg-Ni化合物中的Ca (1.97 Å)元素进行部分取代，系统研究了稀土元素的取代对AB2、AB3和A2B7型Ca-Mg-Ni化合物的相结构、气态储氢性能以及电化学性能的影响。未经取代的Ca-Mg-Ni合金都有着最大的储氢容量，Nd、Gd和Er取代后合金储氢量依次减少；合金的吸氢平台压与平均亚单元体积满足一个线性关系，且线性斜率随着[AB5]单元的增加而减小；合金的吸氢焓变的绝对值随着亚单元体积的减小而降低，氢化物朝着不稳定的方向变化，更加有利于吸放氢过程的进行。稀土元素的取代使Ca-Mg-Ni合金的原子占位更加有序而表现出优异的气态储氢性能和电化学性能，Nd元素的取代具有最好的改善效果，特别是在充放电循环和高倍率放电性能方面。同时还研究了AB3型超点阵合金放氢过程与亚单元体积之间的构效关系，为今后储氢合金的设计提供了很大的参考价值。