高活性锰基氧化物氧还原催化剂的理论设计与构筑

The development of high activity, low cost non-noble electrocatalysts towards oxygen reduction reactions (ORR) is the key for the widespread utilization of fuel cells and metal air batteries. Manganese oxide is considered to be a promising alternative of Pt-based catalysts due to its low cost and well stability. However, it is hampered by inferior activity to noble metals. Therefore, accelerating the exploration of outstanding MnOx catalyst is highly demanded. This project is going to explorer the relationship between electronic structure and activity, systematically search the design principle for MnOx catalyst and propose the descriptor to synthesis of high active manganese oxide catalyst, by combination of first-principles calculation and experiment. Specifically, we will use first-principles calculation to model the oxygen adsorption, calculate the electronic structures of the condensed state and tune the d band structure and the size of the band gap. Based on these results, we will try to interpret the mechanism and propose the design principle as well as descriptor. Subsequently, by synthesis method, we will prepare MnOx nanomaterials with specific active site learned from first-principles calculation. Then optimize the structure and morphology to construct high active MnOx nanomaterials for ORR that is comparable to platinum.

高性能、低成本的非贵金属氧还原催化剂是燃料电池及金属空气电池大规模应用的关键。锰基氧化物（MnOx）催化剂具有成本低、稳定性好等优势，但其性能无法与贵金属催化剂媲美，因此，加快探索高活性MnOx材料，极大提高催化性能是实现其应用的重要前提。本项目以此为切入点，拟通过理论计算与实验研究相结合的方式，研究电子结构与性能的关系，系统性探索研究MnOx催化剂的设计原则，寻找性能“描述因子”，指导实验实现高活性锰基氧化物催化剂的构筑：采用第一性原理计算从分子吸附、凝聚态结构、掺杂等多层次实现Mn元素的d带能带相对位置与禁带带隙的调控，阐明MnOx氧还原催化机制，归纳活性中心构筑的原则和“描述因子”，从理论上指导锰基氧化物催化剂的设计；在理论计算基础上，通过简单的实验手段，可控制备具有特定活性中心的MnOx纳米催化剂，优化材料结构和形貌，实现媲美铂基催化剂的MnOx催化剂的构筑。

过渡金属锰氧化物电催化剂在一次/二次电池、电化学传感器件等领域已得到广泛应用。锰氧化物中Mn的价态，粒径、形貌等直接影响ADMFC阴极性能、稳定性和使用寿命。本项目通过控制制备不同粒径和晶面的Mn3O4，研究了其对ORR的催化行为，探讨Mn3O4电催化剂的活性中心，主要结论如下：采用控制水解法和水热合成-热分解法分别制备了纳米片、纳米粒子（平均粒径为12 nm 、6 nm）及Mn3O4纳米棒。XRD、HRTEM以及XPS等测试结果表明，所制备的样品均为四方结构的Mn3O4。当Mn3O4电催化剂粒径由12 nm减小至6 nm时，Mn3O4电催化剂对ORR的比表面活性提高了约50%。与球形纳米粒子相比，Mn3O4纳米棒对ORR的比表面活性提高了约一个数量级。HRTEM、XPS等表征结合晶面原子排列模型结果表明，随着Mn3O4纳米晶尺寸的增加，Mn3+成为电催化剂的主要活性中心。纳米棒优先暴露{101}晶面，{101}晶面中Mn3+的表面密度最高，从而促进ORR的进行。