基于4d/5d结构过渡金属Pt-M合金催化剂的合成及其氧还原电催化活性和稳定性研究

The commercialization of polymer electrolyte membrane fuel cells (PEMFCs) is severely hampered by the high platinum loading for the oxygen reduction reaction (ORR) as well as its poor durability. It was recently demonstrated that by alloying Pt with 4d and 5d transition metals, i.e., Y, La, Ce and Gd, both the catalytic activity and stability of Pt for the ORR could be greatly improved. Although attractively, their synthesis in the nanoparticle form is particularly challenging owing to the large negative value for the standard reduction potentials of 4d and 5d transition metals. In this project, we propose to synthesize the nanoparticle form of Pt-M@Pt (M=Y, La, Ce and Gd) alloy catalysts in organic solvents using an electrochemical method combined with the underpotential deposition. Then, the influences of transition metal type, Pt:M atomic ratio, particle size, surface structure as well as the thickness of Pt overlayer on the ORR activity and stability will be investigated. Furthermore, the synergistic effect of the elemental composition, particle size and surface structure on both the ORR activity and stability of Pt-M@Pt (M=Y, La, Ce and Gd) alloy catalysts will be clarified. Based on the above studies, it is anticipated that a novel type of Pt-M alloy catalyst with both high ORR activity and stability will be designed，thus accelerating the commercialization of PEMFCs.

为满足质子交换膜燃料电池商业化需求，我们必须进一步降低阴极氧还原的Pt用量并提高其耐久性。基于4d、5d结构过渡金属（Y、La、Ce和Gd）的合金催化剂同时表现出优异的氧还原电催化活性和稳定性，但由于该类过渡金属的标准电极电位很负，其合金纳米颗粒的制备非常困难。本项目将首先开发有机电解液体系的电化学方法和欠电势沉积方法可控制备Pt-M@Pt（M=Y、La、Ce和Gd）合金纳米颗粒，探索过渡金属种类、Pt:M原子比、颗粒尺寸、晶体结构以及表层Pt原子层数等因素对氧还原电催化活性和稳定性的影响。通过阐明元素组成、颗粒尺寸以及晶体结构三者的协同效应对Pt-M@Pt（M=Y、La、Ce和Gd）合金催化剂的ORR电催化活性和稳定性作用规律，进一步指导设计出同时具有高氧还原电催化活性和稳定性的新型Pt-M合金催化剂用于加快质子交换膜燃料电池的商业化。

经过本项目的实施，提出新的有机电解液体系电化学合成方法，阐明其沉积机理，揭示不同有机电解液体系物理化学性质及有机溶剂分子、支持电解质离子和金属前驱体空间结构对电沉积过程的影响规律。基于该新方法制备的Pt纳米催化剂氧还原活性是商业Pt/C的3.23倍。设计氮、氮二甲基甲酰胺（DMF）选择性络合助电沉积高活性PtCo合金催化剂，DMF选择性与Pt离子络合而不与Co离子络合，大大拉近Pt、Co沉积电位差，促进电沉积时高质量PtCo合金相的形成，所得到的PtCo合金催化剂氧还原活性达到是商业Pt/C催化剂的7倍。最后，该项目拓展了同时具有高活性及高稳定性的碱性乙醇氧化电催化剂结构设计新思路，成功利用欠电势置换沉积技术形成表面Au亚原子单层修饰的全新的Pd7Ir@Au/C三元纳米合金催化剂，其碱性乙醇氧化活性增长131%，高催化活性的实现源自于Au亚原子单层对表面原子的电子效应，稳定性的提升得益于表面Au的稳定作用对颗粒表面自由能的降低。