Gas adsorbate-induced Au atomic segregation and clustering from Cu(Au)

气体吸附诱导Cu(Au)合金中Au原子的偏聚和富集

Abstract

Surface compositional and phase segregation in an alloy can change its functionality, especially for applications where surface structure and chemistry play a vital role. For instance, the surface status of alloy catalysts significantly affects their catalytic performance for both heterogeneous and electrochemical processes. Surface segregation is believed to be driven by the difference in surface energy to reduce the total free energy of the alloy. However, the atomistic processes during the segregation process remain elusive, especially for gas molecule-induced segregation, where both structural and chemical reordering may occur. Herein, we achieved in-situ atomic-scale visualization of the surface segregation behaviors of a solid solution Cu(Au) alloy under the CO gas by an aberration-corrected environmental transmission electron microscope. CO-induced Cu(Au) surface ordering structures largely change the surface chemistry of the alloy. Further gas exposure at elevated temperature could facilitate Au atom diffusion through a specific “atomic channel” structure for dealloying and clustering on the surface. The segregated Au nanoparticles show rich phase and morphological dynamics interacting with the alloy surface, where the gas adsorption also plays an important role. These atomic insights provide direct evidence for the surface segregation and dealloying mechanisms of bimetallic alloys, and highlight the role of gas adsorbate in these surface processes.

摘要

合金中的表面成分和相偏析会改变其功能, 尤其是在表面结 构和化学起着至关重要作用的应用中. 例如, 合金催化剂的表面状 态显著影响其在异相催化和电化学过程中的催化性能. 表面成分 偏析被认为是由表面能的差异驱动, 以减少合金体系的总自由能. 然而, 目前合金中成分偏析的原子尺度进程还尚不清楚, 尤其是对 于气体分子诱导的成分偏析, 在该过程中可能同时发生结构和化 学重排. 本文通过像差校正环境TEM从原子尺度研究了固溶态 Cu(Au)合金在CO气氛下的表面偏析行为. CO气氛能够诱导Cu (Au)合金表面形成有序结构, 在很大程度上改变合金的表面化学 性质. 高温条件下, CO气氛会进一步促进Au原子通过特定的“原子 通道”进行扩散, 在合金表面偏聚和富集. 富集形成的Au纳米颗粒 与合金表面在形貌和结构方面发生了丰富的动力学交互作用. 这 其中CO气体吸附也起着重要的作用. 这些原子尺度的研究结果为 双金属合金的表面偏析和去合金化机理提供了直接证据, 并突出 了气体吸附物在这些表面行为中的作用.

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Acknowledgements

This work was supported by the National Natural Science Foundation of China (21873069 and 11504162). The authors would like to thank the Collaborative Innovation Center of Sustainable Energy Materials in Guangxi University for the use of the aberration-corrected HRTEM facility.

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Authors

Contributions

Luo L and Zhang L conceived this study and designed the experiments; Zhang L and Dong Z carried out the sample preparation and series of TEM experiments; Zhang L analyzed all the data and wrote the draft of the paper with the help of all the authors. All authors discussed the results and commented on the manuscript.

Corresponding author

Correspondence to Langli Luo.

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Conflict of interest

The authors declare that they have no conflict of interest.

Supplementary information

Experimental details, supporting data and movies are available in the online version of the paper.

Lifeng Zhang received his PhD degree from the Institute of Metal Research, Chinese Academy of Sciences. Currently, he is a lecturer at the Institute of Molecular Plus at Tianjin University in China. His current research interest focuses on the advanced (S)TEM studies of microstructure, interface and complicated defects in materials to reveal their related processing, structure and properties.

Langli Luo received his PhD degree in materials science and engineering from the State University of New York at Binghamton. He was a postdoctoral fellow at Northwestern University and Pacific Northwest National Laboratory in USA. Currently, he is a professor at the Institute of Molecular Plus, Tianjin University in China. His current research focuses on in situ TEM studies of chemical processes and energy-related materials.

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Cite this article

Zhang, L., Dong, Z., Wang, S. et al. Gas adsorbate-induced Au atomic segregation and clustering from Cu(Au). Sci. China Mater. 64, 1256–1266 (2021). https://doi.org/10.1007/s40843-020-1529-3

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Keywords

  • surface segregation
  • clustering
  • Cu(Au) alloy
  • environmental TEM
  • CO