Han Xiao, Zhou Yanan, Tai Xiaolin, Wu Geng, Chen Cai, Hong Xun, Tong Lei, Xu Fangfang, Liang Hai-Wei, Lin Yue
Hefei National Research Center for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui, P.R. China.
School of Material Science and Chemical Engineering, Institute of Mass Spectrometry, Ningbo University, Ningbo, Zhejiang, P.R. China.
Nat Commun. 2024 Aug 22;15(1):7200. doi: 10.1038/s41467-024-51541-0.
Intermetallic compounds (IMCs) with ordered atomic structure have gained great attention as nanocatalysts for its enhanced activity and stability. Although the reliance of IMC preparation on high-temperature annealing is well known, a comprehensive understanding of the formation mechanisms of IMCs in this process is currently lacking. Here, we employ aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (AC-HAADF-STEM) to track the formation process of IMCs on carbon supports during in-situ annealing, by taking PtFe as a case study within an industry-relevant impregnation synthesis framework. We directly discern five different stages at the atomic level: initial atomic precursors; Pt cluster formation; Pt-Fe disordered alloying; structurally ordered PtFe formation, and final PtFe-PtFe IMC conversion. In particular, we find that the crucial role of high-temperature annealing resides in facilitating the diffusion of Fe towards Pt, enabling the creation of alloys with the targeted stoichiometric ratio, which in turn provides the thermodynamic driving force for the disorder-to-order transition.
具有有序原子结构的金属间化合物（IMCs）作为纳米催化剂因其增强的活性和稳定性而备受关注。尽管IMC的制备依赖于高温退火是众所周知的，但目前缺乏对该过程中IMC形成机制的全面理解。在这里，我们以工业相关浸渍合成框架内的PtFe为例，采用像差校正高角度环形暗场扫描透射电子显微镜（AC-HAADF-STEM）来跟踪原位退火过程中碳载体上IMC的形成过程。我们在原子水平上直接识别出五个不同阶段：初始原子前驱体；Pt团簇形成；Pt-Fe无序合金化；结构有序的PtFe形成，以及最终的PtFe-PtFe IMC转变。特别是，我们发现高温退火的关键作用在于促进Fe向Pt的扩散，从而能够创建具有目标化学计量比的合金，这反过来又为无序到有序的转变提供了热力学驱动力。
