The ionic conductivity of polymer electrolyte membranes (PEMs) is an essential parameter for their device applications. In water-swollen PEMs, protons and other ions are transferred through hydrophilic channels of a few nanometers in diameter at most. Thus, optimizing the chemical and physical properties of the channels can enhance the conductivity of PEMs. However, the factors controlling the conductivity have not been completely clarified. Here, we report that measurements taken near the channel walls by a special nuclear magnetic resonance technique with ≤1 nm spatial resolution showed the largest water diffusivity when ∼80% of hydrophilic sulfonic acid groups were blocked, but the proton conductivity was low. The water diffusivity was much less affected by differences in water content. Our results provide a concept for changing the properties of PEMs and a challenge to implement the improved diffusivity in a way that enhances net ion conductivity.

中文翻译：

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Nafion 聚合物电解质膜中的纳米级水动力学：重新审视分子疏水性和水含量的影响

聚合物电解质膜 (PEM) 的离子电导率是其器件应用的重要参数。在水膨胀的 PEM 中，质子和其他离子最多通过直径为几纳米的亲水通道转移。因此，优化通道的化学和物理特性可以提高 PEM 的电导率。然而，控制电导率的因素尚未完全阐明。在这里，我们报告了通过空间分辨率≤1 nm 的特殊核磁共振技术在通道壁附近进行的测量显示，当 80% 的亲水性磺酸基团被阻断时，水扩散率最大，但质子电导率较低。水扩散率受水含量差异的影响要小得多。