低配位数位点修饰核-壳结构催化剂及其氧化还原反应过程研究

Core-shell structure catalyst is regarded as a promising candidate for application in fuel cells due to the ultra-low Pt loading and ultra-high Pt utilization. It appears that the degradation of transition metal cores in the core−shell catalysts is the major problem under harsh fuel-cell operation conditions. In this proposal, we build a novel core-shell structure of oxygen reduction reaction (ORR) catalyst via underpotential deposition and galvanic displacement method with the low-coordinated surface sites doped by metal oxide, e.g., vertex and edges, and Pt occupying the surface facets. The main tasks of this project are: (1) synthesizing the metal oxide doped core-shell catalysts with tunable composition and structure; (2) developing in-situ characterization methodology for the oxygen reduction process; (3) revealing the effect of catalyst structure on the ORR performance by monitoring the micro-structural and electrochemical dynamics of the synthesized core-shell catalysts; (4) uncovering the reaction mechanism of the oxygen reduction process including the low-coordinated surface sites doping and repulsive interaction between oxygen species. Based on these mechanism studies, rational design and building of the core-shell structure will be carried out for improving the performance of the ORR catalysts. The results will not only provide experimental and theoretical foundations about structure design and optimization of ORR catalysts, but also represent a better understanding of the oxygen reduction mechanism and promote the development of electrochemical metallurgy technology in the field of new energy and new materials.

核-壳结构是减小催化剂中铂（Pt）负载量，提高Pt利用率的最有效途径之一。然而，其内层核金属原子的溶出和表面富集是制约核-壳结构催化剂性能的关键。本申请项目拟采用定点修饰和欠电位沉积-伽伐尼置换的方法构筑低配位数位点修饰的单原子层Pt核-壳结构氧还原反应（ORR）催化剂；通过对催化剂内核结构和制备过程调控，开发特定位点修饰核-壳型催化剂的可控合成方法；对其结构和性能进行表征，分析催化剂微观结构与其ORR催化性能之间的内在联系；研究金属氧化物的锚定作用对核-壳结构催化剂内层核金属原子溶出和表面富集的抑制作用；采用电化学原位表征方法探讨缺陷位点修饰、氧排斥作用对催化剂催化活性和稳定性的影响机制，优化催化剂ORR催化活性和稳定性。项目的开展将为核-壳结构高性能燃料电池催化剂的合成提供一种新思路，加深对氧还原反应过程机理的认识，还能促进电化学冶金技术在新能源、新材料领域的发展，具有重要的科学意义。

针对燃料电池核-壳内层核金属原子的溶出和表面富集制约核-壳结构催化剂性能的问题，采用定点修饰和欠电位沉积-伽伐尼置换的方法构筑低配位数位点修饰的单原子层Pt核-壳结构氧还原反应（ORR）催化剂。研究结果：(1)完成第一性原理电子结构计算，改变内层核金属组成计算Pt 的d 轨道中心能级及Pt−O 结合，改变金属氧化物组成计算Pt 的d 轨道中心能级及Pt−O 结合能，初步选定Ti、Mo、Zr作为氧化物内核的材料。研究实验参数（单体浓度，反应温度、时间，溶液极性，退火气氛、温度和时间，以及表面活性剂种类和用量等），调控催化剂颗粒的粒径和表面晶型等，发展低配位数位点修饰金属纳米颗粒的可控合成方法。(2)系统表征和分析所制备的各种不同组成的核-壳结构催化剂的ORR 电催化特性，包括循环伏安特性、氧还原、耐甲醇性能、稳定性等，分析低配位数位点修饰核-壳型ORR 催化剂的微观结构与其电催化性能之间的内在联系。(3)碳载体的活性对催化剂的最终性能存在较大影响，通过一锅法热解成功地制备了Fe、N、S和F共掺杂的碳载体，其本身即具备优良的氧还原催化性能。发表论文28篇，获授权专利4件，3人晋升职称，培养研究生5人。