Mapping Microscale Chemical Heterogeneity in Nafion Membranes with X-ray Photoelectron Spectroscopy
Mapping Microscale Chemical Heterogeneity in Nafion Membranes with X-ray Photoelectron Spectroscopy
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DOI：
10.1149/2.0771811jes
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发表时间：
2018-08-28
影响因子：
3.9
通讯作者：
Baker, Lane A.
中科院分区：
文献类型：
--
作者：
Friedman, Alicia K.;Shi, Wenqing;Baker, Lane A.
Nafion已经在各种各样的应用中发现了实用性，特别是作为燃料电池技术中最常用的电解质膜。尽管用x射线光电子能谱（XPS）进行了几十年的表征，但文献中存在关于氧结合能从Nafion中存在的醚和磺酸官能团中正确分配的争议。在这里，我们采用高取向热解石墨（HOPG）作为内标来校准所有XPS光谱，并能够将C1s， O1s， F1s和S2p的结合能与Nafion结构相关联。此外，通过薄膜截面的二维XPS映射以及通过Ar+离子溅射的表面烧蚀，揭示了这种配方固有的微尺度非均质性。结果清楚地表明，Nafion膜由两层化学性质不同的层组成：几微米厚的表层由磺酸基组成，内层屏蔽更非极性的全氟醚部分。(C)作者2018。由ECS出版。
Nafion has found utility in a wide variety of applications, particularly as the most commonly used electrolyte membrane in fuel cell technology. Despite decades of characterization by X-ray Photoelectron Spectroscopy (XPS), a dispute exists within literature over the proper assignment of oxygen binding energies from the ether and sulfonate functional groups present in Nafion. Here, we have employed highly oriented pyrolytic graphite (HOPG) as an internal standard to calibrate all XPS spectra and are able to correlate binding energies from C1s, O1s, F1s and S2p to the Nafion structure. Further, microscale heterogeneities inherent to this formulation of Nafion membranes are revealed through two-dimensional XPS mapping of membrane cross-sections as well as surface ablation via Ar+ ion sputtering. Results clearly show Nafion membranes are comprised of two chemically distinct layers: a surface layer several microns thick that is comprised of sulfonate groups and an inner layer that shields the more non-polar perfluoroether moieties. (C) The Author(s) 2018. Published by ECS.