Sodium thiosulfate-assisted synthesis of high-Pt-content intermetallic electrocatalysts for fuel cells

Carbon supported Pt-based intermetallic compounds (IMCs) with high activity and durability are the most competitive cathode catalysts for the commercialization of proton exchange membrane fuel cells (PEMFCs). The synthesis of Pt-based intermetallics with a good balance between small size and high metal loading remains challenging because of the high-temperature annealing that is generally required to form intermetallic phases. We developed a sodium thiosulfate-assisted impregnation strategy to synthesize small-sized and highly ordered PtM IMCs catalysts (M = Co, Fe, Ni) with high-Pt-content (up to 44.5 wt%). During the impregnation process, thiosulfate could reduce H₂PtCl₆ to form uniformly dispersed Pt colloid on carbon supports, which in turn prevents the aggregation of Pt at the low-temperature annealing stage. Additionally, the strong interaction between Pt and S inhibits particle sintering, ensuring the formation of small-sized and uniform PtM intermetallic catalysts at the high-temperature annealing stage. The optimized intermetallic PtCo catalyst delivered a high mass activity of 0.72 A mg_Pt^–1 and a large power performance of 1.17 W cm^–2 at 0.65 V under H₂-air conditions, along with 74% mass activity retention after the accelerated stress test.