STEM-Z衬度像在Au@Pd核壳结构二元合金纳米催化颗粒显微结构表征中的应用

STEM-Z衬度像在Au@Pd核壳结构二元合金纳米催化颗粒显微结构表征中的应用

相晨生¹，宋亚会²，夏海兵²，田  鹤^1*

（1. 浙江大学电子显微镜中心，硅材料国家重点实验室，材料科学与工程学院，浙江 杭州310027；2. 山东大学 晶体材料国家重点实验室，山东 济南 250100）

摘 要  核壳结构二元合金纳米颗粒因其金属间的协同作用具有一些优异的性质，如Au@Pd为例等，是一种应用广泛的催化剂颗粒，目前制备过程中过厚的Pd壳层会降低Pd前驱体的利用效率、催化性能，如何实现对包覆层厚度的调控是研究重点。本文利用STEM-Z衬度像技术，以Au@Pd为研究对象，分别制备了包覆层为1、4、6的Au@Pd纳米催化颗粒。根据STEM-Z衬度像原理，计算出了最优的探测器角度，θ₁、θ₂分别为41.34 mrad及266.03 mrad，在此条件下二者散射截面比为2.93。清晰确定了不同反应条件下的包覆层厚度，并基于表面结构探究了其生长机理及模式：当Pd壳层<4时，Pd的生长符合F-M模式，在4~6层时，其生长模式符合S-K模式，当包覆层>6层时，已经过渡为V-W模式，表面会出现明显的岛状团簇。通过调控前驱体用量实现了对包覆层的精准调控，确定了当包覆层为1层时，纳米颗粒其比表面积可达100.9m²/g，基于Pd计算的质量电流密度可达13.2A/mg，电流密度可达13.1mA/cm²，优于目前商用Pd/C催化剂。实现了对Au@Pd纳米合金颗粒的可控合成。

关键词   扫描透射电子显微术；STEM-Z衬度像；二元合金颗粒；核壳结构

中图分类号：  文献标识码：A      doi:10.3969/j.issn.1000-6281.2020.04.003

The application of STEM-Z-contrast imaging in the characterization of microstructure of the Au@Pd core-shell bimetallic nanoparticles as catalyst

XIANG Chen-sheng¹，SONG Ya-hui ²，XIA Hai-bing ²，TIAN He ^1*

(1. Center of Electron Microscope, State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Zhejiang University, Hangzhou Zhejiang 310027；2. State Key Laboratory of Crystal Materials, Shandong University, Jinan Shandong 250100，China)

Abstract  Core-shell (CS) structured bimetallic nanoparticles (NPs) can have some excellent properties due to the synergistic effects between the metals. For example, Au@Pd NPs have enhanced chemical catalytic activity than either pure Au or Pd. However, thick Pd shells could decrease the efficiency of the Pd precursor and catalytic performance, which prevails in the current synthesis, leading much efforts to control the thickness of the shell. In this paper, Au@Pd NPs with 1, 4, and 6 layers of shell Pd were synthesized respectively. The Z-contrast imaging was used to determine the thickness of the shells formed under different conditions, based on which the growth mode and mechanism were researched. According to the principle of the Z-contrast imaging, best detector parameters were calculated: θ₁、θ₂ are 41.34 mrad and 266.03 mrad respectively, under which the ratio of the scattering cross section could be 2.93. Two elements can be distinguished clearly and the growth modes were researched.When the layers are less than 4, the Pd growth following the F-M mode; when the layers are between 4 and 6, the growth mode changed into the S-K mode, and when the layers are more than 6, it finally transited into the V-W mode. Through finely tuning the amount of the Pd precursor, the best synthesis condition was discovered. The Au@Pd Np with only one layer of shell had the best performance. Our work realized the precise manipulation of the thickness of the shell and controlled growth of the Au@Pd CS NPs.

Keywords  STEM-Z contrast imaging；core-shell structure；bimetallic nanoparticles

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