Ex-Situ Investigation of Membrane Swelling in an Electrolyzer Using X-Ray Tomography

Abstract

In this contribution, we focus on the membrane swelling of a catalyst coated Nafion© 212 in the compound of a polymer electrolyte membrane electrolyzer. So far, the swelling of the catalyst coated membrane (CCM) is mostly investigated isolated from the surrounding components as porous transport layers (PTL) and the flow field plates[1-4]. To explore the swelling, ex-situ tests were carried out, using a special device [5] to control contact pressure and compression and computer tomography. This allowed the swelling of the CCM to be studied at different positions in the structure and at different compression pressures as well as the interaction of the different components. Figure 1 shows a comparison of the dry (a) and (c) and flooded (b) and (d) state of the CCM. The black lines indicate the surface of the CCM. In the flooded state, the thickness of the CCM increases by 20 % from about 50 µm to 60 µm, while the distance of the expanded metal sheets stays constant. This means, that the thickness increase of the CCM results in a decrease of at least one PTL thickness. One main goal of the experiment was to show, whether the swelling of the membrane is dependent or independent of the compression pressure and therefore may cause a different water uptake, which might give an explanation of the decreasing high frequency resistance with increasing pressure [4, 6].[1] Ito, H., Maeda, T., Nakano, A., & Takenaka, H. (2011). Properties of Nafion membranes under PEM water electrolysis conditions. International journal of hydrogen energy, 36(17), 10527-10540[2] Budinski, M. K., & Cook, A. (2010). Osmotic pressure of water in Nafion®. Tsinghua Science & Technology, 15(4), 385-390[3] Kusoglu, A., Kienitz, B. L., & Weber, A. Z. (2011). Understanding the effects of compression and constraints on water uptake of fuel-cell membranes. Journal of the Electrochemical Society, 158(12), B1504[4] Borgardt, E., Giesenberg, L., Reska, M., Müller, M., Wippermann, K., Langemann, M., Lehnert, W., & Stolten, D. (2019). Impact of clamping pressure and stress relaxation on the performance of different polymer electrolyte membrane water electrolysis cell designs. International journal of hydrogen energy, 44(42), 23556-23567[5] Hoppe, E., Janßen, H., Müller, M., & Lehnert, W. (2021). The impact of flow field plate misalignment on the gas diffusion layer intrusion and performance of a high-temperature polymer electrolyte fuel cell. Journal of Power Sources, 501, 230036[6] Stähler, M., Stähler, A., Scheepers, F., Carmo, M., Lehnert, W., & Stolten, D. (2020). Impact of porous transport layer compression on hydrogen permeation in PEM water electrolysis. International journal of hydrogen energy, 45(7), 4008-4014 Figure 1