Monitoring dynamics of defects and single Fe atoms in N-functionalized few-layer graphene by in situ temperature programmed scanning transmission electron microscopy
Monitoring dynamics of defects and single Fe atoms in N-functionalized few-layer graphene by in situ temperature programmed scanning transmission electron microscopy
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DOI：
10.1016/j.jechem.2021.05.005
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发表时间：
2021-06-01
影响因子：
13.1
通讯作者：
Schuster, Manfred Erwin
中科院分区：
文献类型：
--
作者：
Arrigo, Rosa;Sasaki, Takeo;Schuster, Manfred Erwin
在这项研究中，我们的目标是有助于理解的Fe物种的形成过程中，自上而下的合成分散的Fe在N-官能化的几层石墨烯，广泛用于电催化分解。我们使用X射线吸收光谱来确定Fe物种的电子结构和配位几何形状，并结合原子分辨电子能量损失谱原位高角度环形暗场扫描透射电子显微镜来定位这些，确定它们的化学构型并监测它们在热退火过程中的动力学。我们显示了外围Fe原子的高迁移率，首先在石墨烯层的修剪处快速扩散，并且在高达573 K的温度下，从边缘平面向石墨烯层的平面内位置扩散，形成三，四配位金属位点和更复杂的多核Fe物种。该过程通过键C-C断裂发生，这部分地减少了石墨烯域的延伸。然而，绝大多数Fe以金属相形式析出。这种动态的相互转换取决于周围的石墨环境中，这些形成的结构细节，以及铁负载。氮物种出现稳定的孤立和多核的铁物种，即使在温度高达873 K。我们的研究结果的意义在于石墨烯中的单个Fe原子是高度移动的，因此对电活性位点的结构描述是不够的，更复杂的物种可能更相关，特别是在多电子转移反应的情况下。本文提供了这些多核Fe-N位形成的实验证据及其结构特征。(c)2021科学出版社、中国科学院大连化学物理研究所。由ELSEVIER B. V.和科学出版社出版。All rights reserved.这是一个在CC BY许可证下的开放获取文章（http：//creativecommons.org/licenses/by/4.0/）。
In this study, we aim to contribute an understanding of the pathway of formation of Fe species during top-down synthesis of dispersed Fe on N-functionalized few layer graphene, widely used in electrocatal-ysis. We use X-ray absorption spectroscopy to determine the electronic structure and coordination geom-etry of the Fe species and in situ high angle annular dark field scanning transmission electron microscopy combined with atomic resolved electron energy loss spectroscopy to localize these, identify their chem-ical configuration and monitor their dynamics during thermal annealing. We show the high mobility of peripheral Fe atoms, first diffusing rapidly at the trims of the graphene layers and at temperatures as high as 573 K, diffusing from the edge planes towards in-plane locations of the graphene layers forming three-, four-coordinated metal sites and more complexes polynuclear Fe species. This process occurs via bond C-C breaking which partially reduces the extension of the graphene domains. However, the vast majority of Fe is segregated as a metal phase. This dynamic interconversion depends on the structural details of the surrounding graphitic environment in which these are formed as well as the Fe loading. N species appear stabilizing isolated and polynuclear Fe species even at temperatures as high as 873 K. The signif-icance of our results lies on the fact that single Fe atoms in graphene are highly mobile and therefore a structural description of the electroactive sites as such is insufficient and more complex species might be more relevant, especially in the case of multielectron transfer reactions. Here we provide the experimen-tal evidence of the formation of these polynuclear Fe-N sites and their structural characteristics. (c) 2021 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by ELSEVIER B.V. and Science Press. All rights reserved. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).