Innovative Catalyst Design: Fe-Sn-N-C Catalysts for Improved ORR Activity in PEM Fuel Cells

Kurzfassung

Metal-nitrogen-carbon (M-N-C) compounds have emerged as promising catalysts for the oxygen reduction reaction (ORR) at the cathode of high-temperature proton exchange membrane fuel cells (HT-PEMFC) due to their promising activity and tolerance to poisoning by phosphoric acid electrolyte. However, in contrast to commonly used Pt-based catalysts, the activity and stability of Fe-N-Cs in PEMFCs has been found to be significantly lower.[1] In order to address this challenge, Fe-Sn-N-C catalysts based on ZIF-8 have been developed, which show superior ORR mass activities in comparison to the commercial Fe-N-C benchmark (19.3 A g-1 for Fe-Sn-N-C vs. 4.8 A g-1 for PMF-014401 in 0.5 mol L-1 H3PO4 at 0.8 V; Figure 1a).[2] The beneficial role of Sn in improving the performance of Fe-N-C catalysts has been observed. In our recent study, a two-step synthesis route with an intermediate drying step between the doping of each metal was employed.[2] We now report an improved one-pot synthesis that incorporates a ball milling step. This streamlines the process while maintaining the high performance of the catalysts (Figure 1b) and even achieving higher metal contents without obtaining unwanted metal particles. In order to evaluate their performance under realistic operating conditions, we will present gas diffusion electrode half-cell measurements under HT-PEMFC conditions (160 °C, conc. H3PO4). Furthermore, ex- and in-situ X-ray absorption near edge structure (XANES) measurements of the Fe edge will be presented to provide initial insights into the electronic structure of Fe-Sn-N-C catalysts.