空心结构AuPd和CoAuPd催化剂控制合成、表面重构及氧还原性能研究

Fuel cell as a main power candidate for electric vehicles in the future is an important way to ease the energy crisis and environmental problems. Several factors related to the oxygen reduction reaction (ORR) have hindered the development and commercialization of proton exchange membrane fuel cell (PEMFC). Developing low-cost electrocatalysts with high ORR activity and stability and good methanol-tolerance has been a hot issue in the basic research for PEMFC. In this project, galvanic displacement method is used to synthesize binary AuPd and ternary CoAuPd nanocatalysts based on the non-activity of Au and Pd for the oxidation of CH3OH in acid medium. The amount of Pd in the catalysts can be less consumed in aspects of the composition (alloy) and structure (hollow). Subsequently, heat treatment and electrochemical dealloying method will be combined to restructure the surface of the catalysts to improve the ORR activity and stability as well as the utilization of Pd further. The influence of the two kinds of restructure methods to the atom structure of surface of the catalysts will be discussed and optimized. The differences of the electrocatalytic performance between the hollow and solid catalysts, binary and ternary catalysts, before and after the surface restructure process will be analysed and interpreted. The relationship between the composition, structure, restructure degrees of the catalysts and the catalytic activity and stability will be further explored based on these results. The research results of this project will be helpful for theoretical guidance to the controlled synthesis and surface restructure methods of Pt-based PEMFC with low Pt content and high catalytic activity.

燃料电池是未来电动汽车最主要候选电源之一，是缓解能源短缺与环境问题的一种重要途径。氧还原反应是制约质子交换膜燃料电池（PEMFC）发展的主要问题之一，研究低成本、高活性和稳定性以及抗甲醇的氧还原催化剂一直是PEMFC基础研究中的热点问题。本项目利用Au、Pd在酸性体系抗甲醇的本性，采用电位置换法控制合成不同结构二元AuPd和三元CoAuPd纳米催化剂，从结构(空心)和组成(合金)上减少Pd用量。再采用热处理和电化学去合金化相结合的方法重构催化剂表面，进一步提高催化剂活性和稳定性以及Pd的利用率，探讨并优化两种表面重构方法对催化剂表面原子结构的影响。对比分析空心结构和实心结构、二元合金和三元合金、表面重构前后催化剂催化性能的差异，探讨催化剂组成、结构、表面重构程度等与其电催化活性和稳定性之间的关系。本项目研究有助于为低Pd高活性氧还原催化剂的设计合成和表面重构方法提供理论指导。

研究低成本、高活性、高稳定性的氧还原（ORR）催化剂是质子交换膜燃料电池（PEMFC）中的基础核心问题之一。本项目利用三嵌段共聚物P123的还原性和保护性，在不同条件下控制合成了二元AuPd和三元CoAuPd两个体系的催化剂，结果表明，连续还原法能够得到空心结构的AuPd和CoAuPd催化剂，首先从组成（合金）和结构（空心）上减少贵金属Pd的用量。进一步采用电化学去合金化的方法将表面的Co元素溶掉，露出表面富含活性更高的AuPd催化剂。氧还原测试结果表明，空心结构的CoAuPd纳米催化剂在去合金化后的质量和面积电流密度达到81.559 mA mg Pd-1和298.15 μA cm-2，是实心结构CoAuPd催化剂去合金化后的1.15倍，是AuPd的1.27倍。500次循环之后，空心结构的CoAuPd纳米催化剂半波电位和极限扩散电流密度基本没有变化，表现出较好的稳定性。对于二元AuPd催化剂，在Ar氛围在500oC下热处理1小时后，其ORR性能得到了明显提升。三嵌段共聚物特殊的选择性这种合成思路和方法已成功应用到其他二元AuPd、PdRh和三元PtPdRh和PtPdAu等体系。热处理和电化学去合金化相结合的手段是重构催化剂表面结构的有效手段，这种合成思路和重构表面结构的手段有望为合成新型Pd基燃料电池催化剂提供新的途径。