(Invited) Diagnostic Tools to Evaluate Materials for High-Performance PBI Systems

Abstract

Even so, high-temperature PEM fuel cells (HT-PEMFC) based on phosphoric acid doped PBI-type membranes share many similarities with their low-temperature PEM fuel cells counterpart, as they use the same cell chemistry. Additionally, their structure and material selection for the membrane electrode assemblies (MEA) are very similar (1).An essential difference between these two systems is the liquid and, therefore, a mobile electrolyte partially flooding the gas diffusion electrode. The acid distribution within the MEA depends not only on its components but also on the operating conditions. Therefore, it is challenging to manage the acid household effectively for this type of fuel cell. Our collaborators and group members developed novel diagnostic tools to observe the acid distribution within membranes (2), catalyst layers (3, 4), gas diffusion layers (5, 6), and MEAs (7-9) over the past years. These processes occur on various length and time scales. For this reason, different characterization techniques are required to investigate them.For example, the NMR spectroscopy can elucidate phosphoric acid's preferred distribution sites inside the catalyst layer's pore structure. The micropores are filled first, followed by the larger mesopores (3). X-ray computed tomography showed that catalyst and microporous layer cracks are the phosphoric acid's main pathway to exit the cell and contribute mainly to its acid loss (4, 5). Impedance spectroscopy combined with the distribution of relaxation time analyses is one of the few full cell characterization techniques. It is a powerful tool for investigating the acid household to evaluate different catalyst materials (7).References R. Zeis, Beilstein J. Nanotechnol., 6, 68 (2015).F. Mack, S. Heissler, R. Laukenmann and R. Zeis, Journal of Power Sources, 270, 627 (2014).E. Zhang, N. Fulik, H. Zhang, N. Bevilacqua, R. Zeis, F. Xu, E. Brunner and S. Kaskel, Chem Commun (Camb), 57, 2547 (2021).J. Halter, N. Bevilacqua, R. Zeis, T. J. Schmidt and F. N. Büchi, Journal of Electroanalytical Chemistry, 859, 113832 (2020).N. Bevilacqua, M. G. George, S. Galbiati, A. Bazylak and R. Zeis, Electrochimica Acta, 257, 89 (2017).S. Chevalier, M. Fazeli, F. Mack, S. Galbiati, I. Manke, A. Bazylak and R. Zeis, Electrochimica acta, 212, 187 (2016).N. Bevilacqua, T. Asset, M. A. Schmid, H. Markötter, I. Manke, P. Atanassov and R. Zeis, Journal of Power Sources Advances, 7, 100042 (2021).A. Weiß, S. Schindler, S. Galbiati, M. A. Danzer and R. Zeis, Electrochimica Acta, 230, 391 (2017).N. Bevilacqua, M. Schmid and R. Zeis, Journal of Power Sources, 471, 228469 (2020). Figure 1