Nanometer thin films of Nafion ionomer interfaced with platinum form the functional electrodes in many electrochemical devices including fuel cells and electrolyzers. To impart facile proton conduction in a Nafion ionomer, sufficient hydration of the Nafion ionomer is necessary to create a percolating network of water-filled nanometer-sized hydrophilic domains that manifest as macroscopic swelling. This hydration behavior of the ionomer thin films is poorly understood especially for films confined on electrochemically relevant Pt substrates. In this work, we present the evolution of hydration-dependent microscopic hydrophilic domains and macroscopic expansion of a 55 nm thin Nafion film on a Pt substrate. The cross-correlation among the film macro-expansion from ellipsometry, the micro-expansion from GISAXS, and the water distribution from neutron reflectometry (NR) explains the observed non-affine behavior of the film which can be attributed to the randomly and spatially non-uniform distribution of water domains. A correlation between the macroscopic factor (ε/τ) for protonic conductivity, and the domain size and swelling is presented for the first time. In addition, interfacial water between Pt and the ionomer interface is estimated at 75% and 84% RH, and an increase in domain size with RH is discussed to explain the increased activity and oxygen diffusivity with RH.

中文翻译：

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交叉相关的Nafion薄膜受湿度依赖的结构演变，该薄膜限制在铂基板上。

Nafion离聚物的纳米薄膜与铂的界面形成了许多电化学装置（包括燃料电池和电解槽）中的功能电极。为了在Nafion离聚物中提供容易的质子传导，Nafion离聚物的充分水合对于产生充水的纳米级亲水域的渗滤网络是必要的，其表现为宏观溶胀。尤其对于局限在电化学相关的Pt基板上的薄膜，对离聚物薄膜的这种水合行为知之甚少。在这项工作中，我们介绍了水合作用的微观亲水域的演化和Pt基板上55 nm薄的Nafion薄膜的宏观膨胀。椭圆偏振法的胶片宏观膨胀与GISAXS的微观膨胀之间的互相关，中子反射法（NR）的水分布解释了观察到的膜的非仿射行为，这可以归因于水域的随机和空间不均匀分布。首次提出了质子传导率的宏观因素（ε/τ）与畴尺寸和溶胀之间的相关性。另外，Pt和离聚物界面之间的界面水估计为75％和84％RH，并讨论了随着RH畴尺寸的增加，以解释随着RH活性的增加和氧扩散系数的增加。并首次显示了域大小和肿胀。另外，Pt和离聚物界面之间的界面水估计为75％和84％RH，并讨论了随着RH畴尺寸的增加，以解释随着RH活性的增加和氧扩散系数的增加。并首次显示了域大小和肿胀。另外，Pt和离聚物界面之间的界面水估计为75％和84％RH，并且讨论了随着RH畴尺寸的增加，以解释随着RH活性的增加和氧扩散性的增加。