Effect of Fe-N-C Catalysts and Catalyst Layers on High Temperature Proton Exchange Membrane Half-Cell and Single-Cell Performance

Abstract

The high-temperature proton exchange membrane fuel cell (HT-PEMFC) is a promising candidate for conversion of hydrogen e.g., from green reformate and oxygen to electrical energy at temperatures in range of 120-200 °C. However, because of the deactivation of the platinum catalyst due to partial adsorption of phosphates, high Pt loadings up to 1 mgPt cm-2 per electrode are needed which increases the stack production costs.[1] Therefore, Fe-N-C catalysts as promising alternative to Pt materials are under investigation. Thin-film analysis already reveal auspicious oxygen reduction reaction (ORR) activities and high tolerance towards phosphate adsorption and deactivation.[2,3] For characterization of Fe-N-Cs under more realistic conditions, gas diffusion electrode (GDE) half-cell measurements have been established for alkaline and low temperature PEMFC conditions.[4] In this study, GDEs are fabricated by ultrasonic spray (US) and doctor blade (DB) coating employing three different Pt free ORR catalysts and are tested in GDE half-cell and single-cell setups under HT-PEMFC conditions. A commercial catalyst from Pajarito Powder (Fe-N-CPMF), a Black-Pearl-based Fe N ox BP and a phosphoric acid activated rye straw-based Fe-N-aRSH3PO4 catalysts are used. Structural characterization using µ computed tomography shows an up to 50 % higher GDE thickness for DB samples. Implementation of GDEs in HT-PEM half- and single-cells demonstrates that the coating method strongly impacts the half-cell performance and the single-cell performance only minorly, as shown in Fig. 1. This is correlated to different PTFE distributions within the catalyst layers (CL) caused by the fabrication method and differences in phosphoric acid penetration into the CL between half- and single-cell setup. Moreover, high N (10.3 at%) and O contents (9.0 at%) in case of Fe-N-aRSH3PO4 and large catalyst agglomerate size negatively impact the half- and single-cell performances. Thus, this study contributes to the understanding of catalyst and CLs impact of Fe-N-Cs in HT-PEMFCs.

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