基于整体调控的镁镍基核壳型复合储氢材料可控制备及构效关系研究

Magnesium-based alloys are considered as a promising candidate for a new solid hydrogen storage material due to its high storage density, abundant reserves and good reversibility. However, the bottlenecks such as difficulty in activation, sluggish kinetics and high desorption temperature in magnesium alloys have severely limited its further development and applications. In this project, Mg-5at.%Ni is selected as the object and a new way of the overall modification strategy on the basis of micro-alloying is put forward. The internal structure refinement and surface activity for magnesium-rich alloy is achieved through melt-spinning and surface catalysis. To maintain the effect of overall modification, a layer of polymethyl methacrylate is coated on the surface of alloy particles to construct a Mg-Ni-based (PMMA@MWCNTs/TiF3@Mg5Ni) core-shell structure. With the aid of the polymer layer’s selective permeability for H2 against O2 and its elastic coating characteristics, the poison and pulverization processes for Mg-Ni particles are inhibited. Meanwhile the thermodynamics and cycle stability will be ameliorated due to the improved transfer process of heat and mass. The internal/external microstructure evolution for modified magnesium alloys and the isothermal hydrogenation performance will be investigated. The internal/external microstructure evolution and the activation process for modified magnesium alloys will be investigated and explored. The structure-activity relationship between the microstructure and the thermodynamics of the overall modified Mg-Ni core-shell composites will be established. Based on the experimental and theoretical calculation, the of activation mechanism and synergistic catalytic mechanism are revealed. The effect of overall controlling and surface polymer layer coating on the activation and the thermodynamics of magnesium-rich alloys will be discussed, which will establish the basis for the design and modification of a new Mg-based materials with high hydrogen storage capacity.

镁储氢密度高、储量丰富、可逆性好，是一种极具潜力的新型固态储氢材料。然而，活化困难、动力学缓慢及放氢温度高等制约其发展。本项目以Mg-5at.%Ni为对象，提出微合金化基础上的整体改性新途径，即通过溶体快淬及表面催化，实现合金内部结构精细化及表面活性化。为保持整体改性效果，在合金颗粒表面包覆聚甲基丙烯酸甲酯(PMMA)，构筑核壳型镁镍基复合储氢材料 (PMMA@MWCNTs/TiF3@Mg5Ni)，借助有机层的透氢抗氧及弹性包覆特性抑制吸/放氢过程中颗粒的毒化及粉化、改善传质传热、提高热动力学特性及循环稳定性。研究整体调控及有机包覆的镁镍合金表面与内部微结构演变行为并探索活化规律，构建镁镍基核壳型复合材料微结构与吸/放氢热动力学之间的构效关系，基于实验及理论计算揭示活化及协同催化机制，探讨整体调控及表面有机层对富镁合金活化及热动力学的影响规律，为新型高容量镁基储氢材料的设计及改性奠定基础。

能源危机及环境污染日益严重，人们不得不寻求清洁、高效、可循环的新能源“驱动”未来生活。氢能以其热值高、可循环及零排放等特点，得到了越来越多的关注。然而，高效安全的氢气存储技术是氢能源能否广泛推广的关键。镁储氢密度高、储量丰富、可逆性好，是一种极具潜力的新型固态储氢材料。然而，活化困难、动力学缓慢及放氢温度高等制约其发展。本项目以Mg-5at.%Ni为对象，提出微合金化基础上的整体改性新途径，即通过溶体快淬及表面催化，实现富镁合金内部精细化及表面活性化，构筑了镁基复合材料 (MWCNTs/TiF3@Mg5Ni)。借助催化剂MWCNTs的大比表面积及特殊管状结构，加速储氢初始阶段氢气分子的吸附、解离及氢原子的表面渗透过程；并通过TiF3强烈地改善MgH2金属氢化物的异质形核作用，促使MgH2颗粒彼此碰撞接触，形成金属氢化物壳层之前，充分长大，保证了最终的储氢容量。多壁碳纳米管特别是MWCNTs与TiF3耦合作用后，Mg-5at.%Ni合金更容易活化，二者通过氢气分子解离及氢原子辅助扩散的协同催化作用，可促进富镁合金吸氢动力学。内部精细化后的富镁合金在MWCNTs和TiF3表面修饰下，具备了优异的储氢热力学性能和滞后性。60s内可实现高达5.5wt%的氢气储量，并且放氢峰温度可降低至约374℃，相比为催化的富镁合金，降低了约75℃。源于MWCNTs辅助扩散及TiF3表面溢流的协同催化作用是整体改性富镁复合储氢材料取得优异储氢热动力学性能的关键。整体调控镁镍合金表面与内部微结构演变行及协同催化储氢机制的研究，为新型高容量镁基储氢材料的设计及改性提供了新思路，为高容量固态储氢器的设计开发奠定了基础。