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

Abstract

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 activity compared 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 V_RHE, 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.