基于钌基负载的多级孔金属有机骨架化合物的锂-空气电池的基础研究

Lithium (Li)–air batteries have recently attracted a great deal of attention because of their super-high theoretical energy density. However, the sluggish oxygen reduction/evolution reaction (ORR/OER) kinetics on the air cathode much limit the performance of Li–air batteries. The highly effective catalysts can expedite the reaction rate in Li–air batteries. Nevertheless, many current catalysts on the air cathode usually have the low activity, easily promote the side reactions and cannot store enough discharge products, and so on. In this project, to address these above issues, the ruthenium (Ru)-based material-coated metal-organic frameworks (MOFs) with the hierarchical macroporous/microporous structure would be designed. The obtained the Ru-based material-coated hierarchical porous MOFs (Ru-HP-MOFs) have many advantages, including the hierarchical porous structure which can facilitate ionic/oxygen diffusivity and provide efficient buffer space for Li2O2 accommodation, the coordination structure at the molecular level which effectively improves the activity of metal sites and makes these active sites almost impossible to be agglomerated over cycle, and the Ru-based material coating layer which can alleviate undesired side reactions and enhance the surface electronic conductivity. Hence, this proposal aims to construct the highly active and stable catalysts for Li–air batteries. Firstly, the controlled synthesis of Ru-HP-MOFs can be realized through the component optimization and structural design. Then, the inner relationship between the components, morphologies and pore sizes of Ru-HP-MOFs and the electrochemical performances of the Ru-HP-MOFs-based Li–air batteries and the corresponding reaction mechanism are systematically investigated based on electrochemical tests and in/ex situ characterizations. Moreover, the matching performances between the new type electrolytes and the optimized Ru-HP-MOFs catalysts and the reaction mechanism on their interface are also studied in the Li–air batteries. This project will promote the development of Li–air batteries.

锂-空气电池由于具有极高的理论比能量而受到广泛关注，但空气电极上迟缓的氧化还原反应严重制约了锂-空气电池的性能。而高效的催化剂可以有效促进氧化还原反应。针对目前空气电极催化剂活性低，易发生副反应及难以储存放电产物等问题，本项目拟设计钌基负载的大孔/微孔多级孔金属有机骨架化合物(MOFs)。利用其多级孔结构有利于离子/气体的扩散和放电产物的储存，其分子级配位结构有利于提高金属位点的催化活性和避免活性位的团聚以及其钌基负载有利于抑制副反应和提高导电性等优点，旨在构筑一类具有高活性和高稳定性的催化剂。首先通过组分优化和结构设计，实现这类钌基负载的多级孔MOFs的可控合成。其次用电化学测试和原位/非原位表征系统研究其组分，形貌和孔径与锂-空气电池性能的内在关系和作用机理，为催化剂的优化提供理论依据。并探讨新型电解质与优选催化剂的匹配性及其界面上的反应机理。本项目将对锂-空气电池的发展具有促进作用。

锂-空气电池由于具有极高的理论比能量而受到广泛关注，但锂-空气电池中氧还原反应(ORR)和氧析出反应(OER)的动力学缓慢，通常会导致过高的过电位、较低的循环稳定性和较差的速率能力。此外，放电产物导电性差及溶解性低会影响锂-空气电池的可逆性。而且常用的有机液体电解质在敞口的锂-空气电池体系中容易挥发、泄漏并易遭到超氧中间体等的攻击发生分解。因此，开发高效多孔碳基催化剂和新型电解质可以有效解决上述问题。本项目首先合成了一系列贵金属等负载的多孔金属有机骨架(MOFs)衍生物，并将其作为锂-空气电池的催化剂。项目首先详细研究了前驱体和添加异金属的种类等对于多孔MOFs衍生物合成的影响，其次探究了不同碳化温度等实验条件与MOFs衍生物的形貌和金属基纳米颗粒的内在关联。通过上述一系列的反应条件优化等实现了多孔MOFs衍生物的可控合成。随后利用化学还原法或溶胶凝胶法等方法在已合成的多孔MOFs衍生物表面构筑贵金属等修饰层，将其应用于锂-空气电池中。由于源自有机配体的有序多孔碳基质不仅可以加速气体/离子的传输，也可以提供充足的空间储存产物；而有机配体分子水平连接金属离子衍生的高度均匀分布的金属/碳镶嵌结构可以有效促进ORR/OER并抑制反应过程中催化活性位的团聚。而且均匀贵金属基修饰层的引入可以明显降低锂-空气电池中的副反应。因此，可控合成的贵金属等负载的多孔MOFs衍生催化剂极大地提升了锂-空气电池的性能。另一方面，本项目通过紫外或者热聚合等方法构筑了一系列新型聚合物电解质，通过调控锂盐种类或者引入氧化还原电对等优化聚合物电解质组成，并利用电化学测试和原位/非原位表征等相结合的方法详细研究上述电解质对锂-空气电池性能的影响及作用机制，最终得到了与正负极较好匹配的电解质。本项目对今后锂-空气电池催化剂的发展起到了极大地促进作用。在本项目的资助下，共计发表基金标注的SCI论文16篇，包括国内外知名期刊：Advanced Functional Materials、Energy Storage Materials、Chemical Engineering Journal、Journal of Energy Chemistry、 Nano Research等。