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.
Bibliographical noteFunding Information:
This work was supported by the Grant (DRC-14-1-KBSI) of the National Research Council of Science and Technology in Korea to O.H.H., by Ministry of Science, the Grant (C39925) of the KBSI, and Technology Development Program to Solve Climate Changes (NRF-2018M1A2A2063349) through the National Research Foundation of Korea. We thank Dr. SangGap Lee at the Korea Basic Science Institute for the generous loan of an NMR console and informative discussion during the initial construction of a NMR system for the ODNP-NMR system.
Copyright © 2020 American Chemical Society.
All Science Journal Classification (ASJC) codes
- Organic Chemistry
- Polymers and Plastics
- Inorganic Chemistry
- Materials Chemistry