Fe–Sn–N–C Catalysts: Advancing Oxygen Reduction Reaction Performance

Kurzfassung

High-temperature proton exchange membrane fuel cells (HT-PEMFCs) typically rely on platinum-based catalysts, which require high loadings due to Pt deactivation by phosphates from the phosphoric acid-doped membrane. As alternative catalysts for the oxygen reduction reaction, metal−nitrogen-carbons (M−N−Cs) are promising due to their high intrinsic activity and tolerance to phosphates. However, low volumetric activitycompared to Pt nanoparticles on carbon blacks (Pt/C) and insufficient stability limit their applicability. In order to enhance the stability and activity of Fe−N−Cs, this study investigates the incorporation of tin as a second metal, resulting in Fe−Sn−N−Cs, prepared by a metal−organic framework (MOF)-based approach. Stable and highly active catalysts with total mass activities of 8.2 A g−1 (Fe−Sn−N−C (1:1)) and 19.3 A g−1 (Fe−Sn−N−C (1:0.3)) in 0.5 mol L−1 H3PO4, drastically exceeding those of the commercial Fe−N−C catalyst PMF-014401 (Pajarito-Powder, 4.8 A g−1), are obtained by a synthesis without the need for subsequent purification steps. A stress test under harsh conditions (0.6−1.0 VRHE, 10,000 cycles, O2-saturated electrolyte) ascertains stability-enhancing effects of tin, highlighting an increase in stability in conjunction with the tin content. These results provide a valuable contribution to the development of cost-effective HT-PEMFCs by significantly enhancing the catalytic activity of platinum group metal-free catalysts.