钯基纳米晶/氧化物阵列对过氧化锂的引导生长机理及在锂–空电池中的应用

In the organic Li-air batteries, the oxygen reduction reactions (ORR, Li2O2 formation) and oxygen evolution reactions (OER, Li2O2 decomposition) show low kinetics, and the ORR product Li2O2 is insulating and highly reactive with conductive carbon, binder etc. Therefore, developing high-performance catalytic electrodes still remains one of the great challenges for Li-air batteries. In this project, the controlled preparation of Pd-based-nanocrystal/oxide array electrodes and their directing mechanism for Li2O2 growth/decomposition will be investigated. The research project includes three aspects: (1) The effect of preparation conditions on the microstructure of Pd-based-nanocrystal/oxide array electrodes will be studied to achieve the controlled synthesis of the electrodes; (2) the effect of the morphology of the Pd-based nanocrystals, especially the exposed facets, on the growth/decomposition of Li2O2, and the synergistic effect of the characteristics (the crystalline structure, catalytic property, etc) of the oxide supports will be investigated; (3) the effect of the directed Li2O2 growth and decomposition behaviors on the electrochemical performance of Li-air batteries will be investigated. The intrinsic relationships between the components and microstructures of catalytic electrodes, Li2O2 growth/decomposition behaviors, and the performance of Li-air batteries will be clarified based on the combined electrochemical tests and ex-situ/in-situ (in situ TEM) characterizations. The catalytic electrodes will be optimized according to the above research results.

有机系锂–空电池中氧还原（Li2O2形成）/氧析出（Li2O2分解）反应动力学较低，氧还原产物Li2O2的电导率低且与导电碳、粘结剂等反应性较强，因此开发高性能的催化电极是目前锂–空电池面临的重大挑战之一。本项目将研究Pd基纳米晶/氧化物阵列电极的可控制备及该电极对Li2O2生长/分解的引导机制。研究内容包括三个方面：(1)制备条件对Pd基纳米晶/氧化物阵列电极微结构的影响机制，实现阵列电极的可控制备；(2)Pd纳米晶的形态特别是暴露晶面对Li2O2引导生长/分解的作用机制及氧化物载体的特性（晶体结构、自身催化性等）对该机制的协同作用；（3）Li2O2的引导生长/分解行为对锂–空电池电化学性能的影响机制。将电化学测试与非原位及原位（原位TEM）表征相结合，揭示催化电极的组分与微结构、Li2O2的生长/分解行为、锂–空电池性能三者的内在联系。在此基础上，优化催化电极的设计。

在本研究项目中，采用水热法结合热处理工艺成功制备了多种氧化物或贵金属基复合催化剂，包括管状的MnO2/CNT阵列，三明治结构的石墨烯/Au纳米颗粒/Au纳米薄膜，编织结构的Ru/Co3O4阵列，分级结构的Pd/MnO2和IrO2/MnO2、NiCo2O4/MnO2、黑磷量子点/MnO2等催化剂。通过系统的电化学测试结合微结构表征，解明了贵金属种类、形状和取向对Li2O2形核/生长和分解的催化机制，氧化物(特别是MnO2)或碳材料对Li2O2生长/分解的协同催化机制，以及该机制与锂‒氧电池电化学性能的内在关系。在此基础上，通过原位TEM分析，第一性原理计算，Zeta电位测试等手段解明了复合催化剂的催化机制，特别是协同催化机制。通过解明催化机制和优化催化剂设计，实现了锂‒氧电池电化学性能的突破。在解明贵金属基催化剂的基础上，进行了非贵金属基复合催化剂的设计和催化机制分析，解明了其与贵金属的催化机制和催化性能的内在差别。除了研究在氧气中的性能，还研究了在二氧化碳中的性能。在研究催化正极的基础上，设计了金属锂/氟化碳复合负极。初步的研究发现，通过锂负极进行氟化碳修饰，可进一步提高了锂‒氧电池的性能，并通过原位光学显微镜分析，第一性原理计算初步解析了其内在的作用机制。这些研究结果对高性能锂‒空电池的设计具有指导意义。