Mg-Al-Li基合金制备及吸放氢热力学调控研究

In the proposal, the Mg-Al-Li based alloys will be prepared by optimizing solid-phase sintering, mechanical chemistry solid state milling and heat treatment process. The influence of preparation process on the phase structure of the Mg-Al-Li based alloy and phase structure tuning on hydrogen storage properties will be investigated Furthermore, non-equilibrium processing technology for thermodynamic tuning of hydrogen absorption/desorption will be explored. . In order to identify hydrogen storage phase which is too stable hardly react with hydrogen during hydrogenation, the XRD analysis will be carried out before and after alloy hydrogenation/dehydrogenation reaction. To promote hydrogenation reaction related to the hydrogen storage phase, both adjusting preparation process and regulating alloy phase structure will be done.. The thermodynemic properties of hydrogen absorption/desorption , including reaction enthalpy and phase transition et al, will be investigated based on PCT, TGA and DSC testing. According to hydrogen absorption/desorption reaction enthalpy obtained, we adjust component of the Mg-Al-Li based alloy so that can explore thermodynamic tuning of intermediate catalytic phase, formed by adding element and alloy matrix element, on working temperature of hydrogen absorption/desorption.. The first principle density function calculation will be applied to electronic structures of the Mg-Al-Li based alloy and hydride, mechanism of hydrogenation reaction. The thermodynamic stability of alloy hydrogen storage phase, thermodynamic function, the frontier molecular orbital structure and transition state structure of hydrogenation reaction will be investigated, which will provide a theoretical basis for thermodynamic tuning of hydrogen absorption/desorption of the Mg-Al-Li based alloy.

通过固相烧结、机械化学固态球磨、热处理等工艺优化制备Mg-Al-Li基合金，研究制备工艺对Mg-Al-Li基合金相结构的影响以及相结构对储氢性能的调控；探索非平衡加工技术对合金吸放氢的热力学调控。对合金氢化反应前后及放氢后进行XRD分析，明确在氢化过程中过于稳定不易氢化的储氢相，通过调整制备工艺，调控合金相结构，以促进相关储氢相的氢化反应。根据PCT等性能测试，研究吸放氢过程的热力学特性；通过TGA、DSC测试，研究合金吸放氢反应焓和相变，根据吸放氢反应焓调整Mg-Al-Li基合金组成，研究添加元素与合金基体元素形成的中间催化相对吸放氢过程工作温度的热力学调控。开展Mg-Al-Li基合金及氢化物电子结构、氢化反应过程机理研究；从电子结构分析合金储氢相热力学稳定性，研究合金氢化反应前线轨道结构、过渡态结构、以及氢化反应过程热力学函数，为Mg-Al-Li基合金吸放氢热力学调控提供理论依据。

Mg、Al、Li氢化物储氢量高，若作为储氢材料，MgH2和LiH热力学性能太稳定，虽然AlH3具有较低的放氢温度，但氢化反应需要在2.5GPa氢压下进行。本项目探索通过制备工艺优化及催化增强对储氢相结构调控和吸放氢热力学调控，制备高储氢量、良好吸放氢热力学、动力学性能的Mg基储氢材料。同时，开展Mg基合金氢化反应过程与机理的第一性原理理论研究，为Mg基合金吸放氢热力学调控提供理论依据。.制备了系列还原氧化石墨烯负载过渡金属纳米复合材料，rGO框架中嵌入镍可以阻止石墨烯的堆积，石墨烯和Ni纳米颗粒的协同催化作用改善了Mg-Ni@rGO复合材料储氢性能；Y2O3纳米颗粒为形成镁基氢化物提供很多的氢分子渗透通道和活性成核位点、石墨烯的高表面积和高密度缺陷位点增加了氢原子的扩散通道。Y2O3-rGO催化剂有利于改善Mg-Al合金的储氢热力学动力学性能。 研究了MOF对Mg基材料的催化作用，由于ZIF-67的框架结构为Mg/ZIF-67的吸放氢提供了大比表面积，提高了Mg/ZIF-67纳米复合物的氢化活性，Mg/ZIF-67纳米复合物核壳结构的阻止了镁纳米颗粒的团聚，提高了吸放氢循环稳定性。Mg-Li固溶体在氢化反应中是可逆的，添加Si有Mg2Si相形成，Mg2Si作为催化剂降低了Mg-Li固溶体吸放氢过程反应势垒，促进可逆氢化反应并提高了Mg-Li固溶体吸放氢过程的动力学和热力学性能。.利用DFT研究了氢在Mg17Al12表面的吸附和渗透。氢更倾向于吸附在Mg17Al12表面的Mg- Mg桥位上。在次表面，氢的扩散行为变得更加容易，氢渗透到两个表面的最佳扩散势垒接近于0.70 eV。Ni原子掺杂更倾向于吸附在Mg17Al12的Mg3-Mg3桥位点上，占据掺杂Ni的结构中的Mg3位点上。Mg17Al12表面氢化性能的改善是由于吸附能的改善和对Ni作用的离解和渗透障碍的减少。在Mg17Al12表面上加入Ni可以提高原子和分子氢的吸附能，Ni吸附体系表现出较好的氢解和渗透性能。