“固溶-催化-限域”耦合诱导氢化镁储氢性能增强机制与调控

Magnesium hydride MgH2 is a potential on-board hydrogen storage material due to its high hydrogen storage capacity, low cost and abundant resource. However, its application is limited by some drawbacks such as high dehydrogenation temperature, sluggish hydriding/dehydriding rate and poor cycling stability. In this project, a strategy based on the coupled solid-solution, catalysis and confinement for improving the hydrogen storage performance of MgH2 is proposed. The thermodynamic stability of MgH2 will be weakened through the internal solid-solution of trace transition metals in MgH2. The hydriding/dehydriding kinetic barrier of MgH2 will be decreased through the surface catalysis of nonmetal-doped graphene on MgH2. The particle dispersion and environmental stability of MgH2 will be improved through the integral confinement of reticular and defective structure of graphene on MgH2, which will result in the enhanced cycling stability. The selection and design criteria of solid-solution element and doped graphene will be explored. The synergetic modification rule and performance enhancement mechanism of transition metal elements and nonmetal-doped graphene on the thermodynamics, kinetics and cycling stability of MgH2 will be studied. Furthermore, the precise regulation of hydrogen storage performance of MgH2 will be realized based on the coupling effect of solid-solution, catalysis and confinement through the optimization of materials component and processing parameters. The research results in this project are expected to break through the limitation of synergistically improving the hydriding/dehydriding thermodynamics, kinetics and cycling performance of MgH2 and keeping its high hydrogen storage capacity, which is difficult to realize by using conventional modification methods. Meanwhile, these results will provide the new avenue and theoretical basis for the design and development of magnesium based hydrogen storage materials with excellent comprehensive performance.

储氢量大、成本低、来源广的氢化镁MgH2是一种极具应用前景的车载储氢材料，但放氢温度高、吸放氢速率慢、循环稳定性差限制了其应用。本项目提出固溶-催化-限域耦合的MgH2储氢性能改性策略，利用微量过渡金属在MgH2“体内固溶”，削弱MgH2热力学稳定性；利用非金属掺杂石墨烯对MgH2“表面催化”，降低MgH2吸放氢动力学势垒；同时利用石墨烯的网状缺陷结构对MgH2“整体限域”，提高MgH2颗粒分散性与环境稳定性，改善其循环稳定性能。项目探索固溶元素与掺杂石墨烯的选择设计准则，研究二者对MgH2吸放氢热、动力学及循环性能的协同改性规律与性能增强机制，并通过优化材料组分及工艺参数，实现基于固溶-催化-限域耦合的MgH2储氢性能的精确调控。项目研究成果有望打破传统改性方式难以协同改善MgH2吸放氢热、动力学及循环性能且兼具高氢容量的局限性，为综合性能优异镁基储氢材料的设计开发提供新思路与理论依据。

氢能是一种洁净的能源载体，提供安全、高效、经济的氢储存技术是氢能规模化应用的关键。氢化镁MgH2因具有储氢容量高、质轻价廉、资源丰富等被认为是一种理想的固态储氢材料，但其放氢温度高、吸放氢速率慢、循环稳定性差限制了其应用。本项目选取合金化元素与异质原子掺杂石墨烯作为添加剂，采用理论计算与实验研究相结合的方法，系统研究了二者对MgH2储氢性能的固溶-催化-限域耦合改性规律及机理。首选采用第一性原理计算方法，研究了过渡金属在MgH2中的固溶掺杂能力及其对MgH2相结构稳定性与脱氢性能的影响，筛选出具有显著去稳效果的固溶掺杂元素；进一步研究了非金属原子以及部分金属原子在石墨烯中的掺杂能力，在此基础上通过构建界面模型并进行能量计算，研究了掺杂石墨烯对MgH2脱氢焓、脱氢能垒以及石墨烯与MgH2界面结合强度的影响，筛选出对MgH2具有优异催化-限域效果的掺杂石墨烯。基于理论计算结果合成掺杂石墨烯，分别制备出过渡金属添加、掺杂石墨烯复合、以及过渡金属与掺杂石墨烯共同复合的MgH2基储氢体系，基于对其微观组织与储氢性能表征，从实验上验证理论计算结果，并制得了储氢性能优异的MgH2基储氢复合材料，明确了合金化元素与掺杂石墨烯对MgH2储氢性能的固溶-催化-限域耦合改性规律，并结合电子结构计算分析其改性机理，发现固溶元素致使MgH2中的Mg-H键强削弱，体系稳定性降低，而异质原子掺杂石墨烯后，促进了石墨烯与MgH2间的界面电荷转移，一方面增强了二者之间的界面结合强度，另一方面使MgH2内部电荷重新分配，进而降低了H与H重组成H2并脱附的反应能垒。此外，还拓展研究了镁基氧化物、稀土元素以及稀土与碳材料共同添加对MgH2储氢性能的影响及机理。研究结果为高性能镁基储氢材料的设计开发提供了新思路与理论依据。项目执行期内以第一和通讯作者发表SCI论文21篇，申请发明专利6项，其中授权3项，培养硕士毕业生6名。