Low resistive electrolyte membranes are important to improve fuel cell performance and they are indispensable for fuel cells, especially for automotive application, which are used under elevated temperature and low humidity conditions. There are some approaches to lowering membrane resistance in fuel cell operation. From a view point of the membrane design, increasing the ion-exchange capacity^{1, 2} and employing a thin membrane ³ are promising ways to decrease resistance. Although both are effective in improving fuel cell performance, they are not desirable in terms of mechanical durability in fuel cell operation. In reality, reinforced membranes made of perfluorinated sulfonic acid (PFSA) polymer and ePTFE have been widely used in fuel cell sytem³. However, relationship between mechanical properties of PFSA polymers and mechanical durability of unreinforced PFSA membranes is not yet well understood.

In this study, focusing on the backbone and cluster structure of the polymer, we synthesized PFSA polymer electrolytes with various mechanical properties and high proton conductivity as shown in Fig. 1, and investigated their mechanical properties and mechanical durability when used in a membrane electrode assembly. Various polymer properties were obtained, including work of fracture, ratio of yield stress to breaking stress, water uptake, and creep characteristics, which were compared with the results of RH cycling test. Though we couldn’t explain the results of RH cycling test using a single mechanical property, we found a clear relationship between a combination of four mechanical characteristics and the mechanical durability.

Acknowledgement

This research was partially funded by ImPACT Program of Council for Science, Technology and Innovation (Cabinet Office, Government of Japan).

References

1. S. Kinoshita, T. Tanuma, K. Yamada, S. Hommura, A. Watakabe, S. Saito, and T. Shimohira, 226^th Meeting of The Electrochemical Society, 1195 (2014).
2. S. Kinoshita, T. Shimohira, A. Watakabe, S. Hommura, S. Saito, T. Tanuma, and K. Yamada, 26^th PRiME, 2414 (2016).
3. B. Kienitz, J. Kolde, S. Priester, C. Baczkowski, and M. Crum., ECS Transactions, 41(1), 1521 (2011).