强耦合钙钛矿型La1-xCaxCoO3 /石墨烯复合材料的制备及其氧电催化协同效应

Perovskite La1-xCaxCoO3 possess reasonable electro-catalytic activities for oxygen reduction/evolution with low cost and abundant, which is considered to be the most promising bi-functional catalyst for replacing expensive noble metals such as Pt, Au, Pd and Rh in alkaline medium. However, the bottlenecks of the sluggish kinetics and cycle life performance in oxygen electrode, which are caused by low specific area and poor electronic conductivity of the perovskites catalyst, must be broken. Developing facile and low cost fabrication strategy of perovskites with higher catalytic activity for large-scale practical application is still a big challenge. In this project, utilizing the advantages of complexation and hydrothermal method, the chemical complexation-hydrothermal synthesis was proposed to prepare strongly coupled perovskite La1-xCaxCoO3/graphene as bi-functional catalysts. The low specific area and poor electronic conductivity of this perovskite will be improved by anchoring on the surface of graphene. The distribution of the precursors (metal hydroxides) and the low of the perovskite-nanocrystal growth on graphene with various degrees of oxidation could be systematically investigated. The relationship between the content, composition, microstructure of perovskite on graphene and its bi-functional catalytic activities will be established. The synergistic effects of perovskite and graphene for oxygen reduction and evolution will be further illustrated. The project will provide the design of high-performance catalysts for oxygen reduction and evolution with experimental basis and theoretical supporting.

钙钛矿型La1-xCaxCoO3具有价格低廉、原料丰富以及氧还原和析出电催化活性等优点，被电化学领域认为在碱性条件下是可替代铂、金、钯和铑等贵金属的最有发展前景的电催化剂。突破比表面积小和电子电导率低等引起的氧还原/析出动力学缓慢、循环性能差的瓶颈，进一步提高La1-xCaxCoO3的电催化活性是实现其规模化应用的关键。本项目结合石墨烯比表面积大和电子电导率高的特点，综合利用化学络合和水热法的优点，提出化学络合修饰-水热重结晶法制备强耦合钙钛矿La1-xCaxCoO3/石墨烯复合催化剂，系统研究金属氢氧化物前驱体在氧化石墨烯表面的分布情况及晶体在石墨烯表面的生长规律，构建石墨烯表面钙钛矿型催化剂含量、组成、微观结构与氧催化活性之间的关系，阐明La1-xCaxCoO3/石墨烯复合材料对氧催化的协同效应，为制备高性能的双效氧电极催化剂提供实验和理论支撑。

钙钛矿型La1-xCaxCoO3具有价格低廉、原料丰富以及氧还原和析出电催化活性等优点，被电化学领域认为在碱性条件下是可替代铂、金、钯和铑等贵金属的最有发展前景的电催化剂。突破比表面积小和电子电导率低等引起的氧还原/析出动力学缓慢、循环性能差的瓶颈，进一步提高La1-xCaxCoO3的电催化活性是实现其规模化应用的关键。本项目首先研究了化学络合修饰—水热重结晶法制备出了不同质量比例的La1-xCaxCoO3/石墨烯复合材料，并测试该系列催化剂的活性发现其电子转移数n=2.8，仍以“二电子”反应为主，与商业化的Pt/C之间差距较大，主要是由于水热过程较为复杂无法对材料的纯度和相偏析进行控制而导致的。于是本项目改变制备思路，采用了原位化学还原法制备La1-xCaxCoO3/石墨烯复合材料，该法先制备出了高纯度的La1-xCaxCoO3再将其与氧化石墨烯溶液混合，接着原位将氧化石墨烯还原成为石墨烯。研究发现，钙钛矿型氧化物La1-xCaxCoO3能高度均匀地分散在石墨烯表面，使其比表面积从210 m2/g提高到了486 m2/g，并测试该系列催化剂的活性发现其电子转移数n=3.9，使其改变为“四电子”反应，其催化活性与商业的Pt/C相媲美，而循环稳定性和循环寿命都远远的高于Pt/C，达到了200次循环。