Effect of Different Fe-N-C Catalysts on the Performance and Stability of HT-PEMFCs

Kurzfassung

High electrode loadings up to 1 mgPt cm-2 are commonly used in high temperature proton exchange membrane fuel cells (HT-PEMFC) due to partial deactivation of the Pt catalyst by phosphates [1]. At this point, the implementation of less expensive Fe-N-C catalysts for the oxygen reduction reaction in HT-PEMFCs can significantly reduce the material costs. However, a decrease in performance of Fe-N-C-based HT-PEMFCs within the first hours of operation was reported for Black Pearls (BP)-based Fe-N-Cs [2]. In this study, the effect of different Fe N-C types on their stability in HT-PEMFCs is evaluated and degradation processes are identified. A commercial catalyst (PMF 011904, Pajarito Powder), a BP- and two activated biomass-based Fe-N-Cs are implemented as cathode catalysts [3]. Single-cell tests with begin of test characterization followed by 90 h operation at a constant load of 0.1 A cm-2, cyclic voltammetry (CV) and end of test characterization are performed. While initial cell performances display significant differences, the performance decay after 24 h of operation is comparable for all cells. There, an overall performance loss of up to 26 % is observed. Electrochemical and physical post mortem analysis of the cathodes using CV, transmission electron microscopy and mass spectroscopy with inductively coupled plasma reveal, that deactivation of Fe-Nx sites is the main degradation process and corrosion of carbon support is negligible. This study helps to understand degradation phenomena of Fe-N-Cs in HT PEMFC. Moreover, approaches for the optimization of this catalyst class to increase the stability and to the overall Pt loading in HT-PEMFCs is given. [1] R. Zeis, Beilstein J. Nanotechnol. 2015, 6, 68. [2] Y. Hu et al., Appl. Catal. B 2018, 234, 357. [3] J. Müller-Hülstede et al., J. Power Sources 2022, 537, 231529.