镁基核壳结构复合储氢材料的构建及其储氢过程的原位TEM研究

Mg-based material is one of the most promising candidates for solid hydrogen storage. However, the high dehydrogenation temperature, sluggish kinetics and poor cycle performance limited its application, and its deep mechanism is not clear. Reducing the particle size of Mg/MgH2 can reduce the enthalpy of dehydrogenation by introducing free energy and improve its kinetics by shortening H diffusion distance. Doping catalysts can enhance the kinetics by modificating the surface states. In-situ TEM can directly observe the nucleation process, morphology/volume change, phase change, valence state and distribution change during the hydrogen absorption and desorption process. This project will study on a core-shell structured nano Mg/MgH2 @ Ti-based catalyst to dual duning the thermodynamics and kinetics by dual controlling the thickness of Ti-based catalys in shell and particle size of nano Mg/MgH2 in core. At the same time, with the help of TEM in situ characterization techniques, the dynamic evolution of the microstructure, phase structure, valence state and the distribution during Mg/MgH2 hydrogenation and dehydrogenation can be obtained with the change of the temperture, H2 pressure and time. And the nucleation process of Mg/MgH2 can be determined, the composition, distribution, valence state and distribution of catalyst and Mg/MgH2 during the interaction can be obtained. Hence, the binding effect of catalyst on Mg/MgH2 with in different particle size and catalyst mechanism can be confirmed. The dual control mechanism of core and shell for thermodynamics and kinetics can be revealed.

Mg基储氢材料是最有应用前景的储氢材料之一，然其循环性能、脱氢热力学、动力学仍难以满足服役要求，其深层次的储氢机理也不清晰。减小Mg/MgH2的颗粒尺寸能引入自由能而降低脱氢焓，缩短H扩散距离而改善动力学。添加催化剂能改善Mg/MgH2的表面状态，改善其动力学。原位TEM可以直接捕获吸放氢过程的形核过程、形貌/体积变化、相变及价态和分布变化。本项目拟通过构建核壳结构Ti基催化剂包覆纳米Mg的复合体系，并通过调控壳层催化剂的厚度及核层纳米Mg/MgH2的尺寸来调控其弹性应力约束及夹持效应的效果、额外自由能的大小以及H扩散距离，实现热力学和动力学的双调控；借助原位TEM等手段研究不同核层Mg/MgH2的颗粒尺寸在不同厚度的壳层催化剂作用下随温度、时间及氢压变化下的形核过程及结构演变（形貌/体积变化、价态及分布）规律，理解壳层催化剂的催化机制以及约束机理，揭示核壳两层双尺度的调控机制。

Mg基储氢材料是最有应用前景的储氢材料之一，然其循环性能、脱氢热力学、动力学仍难.以满足服役要求，其深层次的储氢机理也不清晰。本项目拟通过构建类核壳结构Ti基催化剂包覆纳米Mg的复合体系，通过调控核层尺寸大小及壳层催化剂的微观包覆结构来调控其弹性应力约束及夹持效应的效果、额外自由能的大小以及H扩散距离，最终实现热力学和动力学的双调控，获得六组平均尺寸尺寸为5 nm、13 nm、22 nm、35 nm、75 nm以及1000 nm的N-Mg-Ti储氢材料，其中N1-Mg-Ti材料在250 °C下3 min可基本完成吸氢，0.6h可基本完成脱氢（5.3 wt%），且经10次循环性能未发生衰减，结构保持良好；借助原位TEM等手段获得不同核层颗粒尺寸N-Mg-Ti储氢材料脱氢过程的结构演变规律，重新认识影响动力学的关键因素，最终确认当颗粒尺寸在1 μm下，Mg/MgH2的表面状态、与催化剂结合的方式、多价态复合型催化剂之间转变的能垒是影响其动力学性能的关键因素。