Li-Mg-N-H体系储氢材料的高效催化及其机理研究

The over-consumption of fossil fuel recently have caused serious energy crisis and environment pollution, which compel us to exploit clean renewable energy. Hydrogen energy has been considered as one of the most ideal secondary energy. However, how to store it in a safe, efficient and economical manner remains a main bottleneck for its large-scale applications currently. In this project, we will take the Li-Mg-N-H system, one of the most promising hydrogen storage systems, as research object, and study its efficient catalysis and corresponding mechanisms in detail. The fundamental research contents are as follows: A) the catalytic modification mechanisms of different alkali metal-based compounds in Mg(NH2)2-2LiH system, B) the synthesis of nano-sized alkali metal-based modifiers and their functional mechanism on Li-Mg-N-H system, C) synergistic mechanism of different kinds of catalysts in Mg(NH2)2-2LiH system. The purpose of this proposal is to illuminate the reason for the different alkali metal-based modifiers having different modification effect, and reveal the synergetic modification mechanisms of multiphase catalysts in Mg(NH2)2-2LiH system. Simultaneously, this study will develop new efficient catalysts and modification technologies, and then provide theoretical and experimental basis for further research of enhancing the hydrogen storage properties of the Mg(NH2)2-2LiH system.

化石燃料过度消耗导致的能源危机和环境问题迫使人们开发清洁可再生能源，氢能是未来最理想的二次能源之一。然而，如何安全、高效、经济地储存氢气是目前氢能实现大规模应用的瓶颈。本项目拟以未来最有望实现大规模车载应用的Li-Mg-N-H体系储氢材料为研究对象，对其开展高效催化及相关机理的基础研究。具体研究内容包括：不同碱金属基化合物对Mg(NH2)2-2LiH体系的催化作用机制及其催化效果存在差异的内在原因；高效碱金属基催化改性剂的纳米化合成及其对该体系储氢性能的影响规律；不同种类催化改性剂对Mg(NH2)2-2LiH体系的协同作用机理。本项目的研究旨在阐明不同碱金属基化合物及其纳米化前后对Mg(NH2)2-2LiH体系储氢性能改善效果存在差异的内在原因，揭示出多相催化改性剂对该体系存在协同改性效果的机理，开发新型高效催化改性剂和催化改性技术，为进一步提高该体系储氢性能的研究奠定理论和实验基础。

Mg(NH2)2-2LiH体系储氢材料具有较高的储氢容量和较适宜的热力学性能，并且其吸放氢过程完全可逆，是目前最有望实现大规模实用化的固态储氢材料之一。但是，该体系储氢材料在吸放氢过程中存在较高的动力性壁垒。催化改性、纳米化和成分调变是改善Mg(NH2)2-2LiH体系储氢性能的重要手段。本项目采用络合催化法成功制备出了微纳态的KH，微纳KH的添加可以显著改善Mg(NH2)2-2LiH体系的储氢性能，并且其对该体系的催化改性效果比商用大颗粒KH更好。通过水热法合成出了亚微米线状的KTiO2(OH)，将其引入Mg(NH2)2-2LiH体系后，样品的吸放氢性能得到显著改善，并揭示了KTiO2(OH)改善该体系储氢性能的机理。此外，还成功制备出一系列锂钾复合氨基物，并从成分调变的思路出发，合成设计出成分为Li3K(NH2)4-xMgH2 (x = 1, 2, 3, 4)的新型Li-Mg-N-H基储氢材料，其中Li3K(NH2)4-2MgH2样品表现出最佳储氢性能。同时，也考察了该新型储氢体系的放氢反应机理。首次将K基催化改性剂以Li3K(NH2)4形式引入Mg(NH2)2-2LiH体系中，并揭示了相应的反应机理。系统研究了NaH、KH、RbH、CsH四种碱金属氢化物对Li-Mg-N-H体系吸放氢性能的影响，获得了不同碱金属氢化物在该体系放氢和吸氢过程中的催化改性效果规律。本项目资助的研究结果对进一步研究和开发储氢材料的高效催化改性剂具有重要的参考价值。