Towards the Performance and Stability of Different Fe-N-C Catalysts in the High Temperature Proton Exchange Membrane Fuel Cell

Kurzfassung

The operation temperature of around 160 °C of the high temperature proton exchange membrane fuel cell (HT-PEMFC) enables a higher tolerance towards contaminants like CO. This makes the operation with reformate from green methanol possible, which is beneficial for volume critical application. However, due to the presence of phosphates from the acid-doped polymer membrane the commonly used expensive Pt catalyst is partly poisoned making high Pt loadings up to 1 mgPt cm-2 per electrode inevitable [1]. At this point, less expensive Fe-N-Cs provide a promising alternative to Pt based catalysts with a better tolerance towards phosphates. In this study, we present a comparison of four Fe-N-Cs towards their application in HT-PEMFC. This includes a commercial PMF catalyst (Pajarito Powder, 011904), a Black-Pearl (BP)- and two activated biomass-based Fe-N-Cs. Physical characterization reveals homogenous Fe and N distribution, higher contents of oxygen-containing functional groups for biomass-based Fe-N-Cs and differences in porosity [1,2]. Mass activities of the Fe N Cs determined by thin-film analysis in 0.5 M H3PO4 display values in range of 1.2-2.5 A g-1 (at 0.8 VRHE). The implementation of the Fe N Cs in gas diffusion electrodes (GDE) results in more inhomogeneous GDE structures for the biomass-based Fe N Cs [3]. Moreover, the application of these GDEs as cathodes in HT-PEM single-cells show the lowest performances within this series. A constant load HT-PEMFC test over 90 h shows strong performance losses of 15 26 % within the first 24 h for all Fe-N-Cs. Cyclic voltammetry after 50 h, end of test characterization as well as post-mortem analysis of membrane electrode assembly (MEA) e.g. using µ computed tomography (µ-CT) are used to identify degradation processes like carbon corrosion. This study helps to understand the impact of catalyst and GDE structure on HT-PEMFC performance and stability which is necessary for further catalyst and GDE developments. [1] R. Zeis, Beilstein J. Nanotechnol. 2015, 6, 68. [2] J. Müller-Hülstede, D. Schonvogel, H. Schmies, P. Wagner, A. Dyck, M. Wark, ACS Appl. Energy Mater. 2021, 4, 7, 6912. [3] J. Müller-Hülstede, T. Zierdt, H. Schmies, D. Schonvogel, Q. Meyer, C. Zhao, P. Wagner, M. Wark, J. Power Sources 2022, 537, 231529.