Multistep Antimony-Seeded Pathway to Catalytic High-Entropy Skutterudite-Type (CoNiRhIrRu)Sb₃ Intermetallic Nanoparticles

High-entropy intermetallic compounds combine the merits of crystallographically ordered structures with the random occupation of distinct crystallographic sites by the constituent metals. Nanoparticles of high-entropy intermetallic compounds are starting to emerge as intriguing materials for applications in catalysis, due to the combination of high surface area-to-volume ratios with their structural characteristics that differ from alloys. However, little is known about how high entropy intermetallic compounds form as nanoparticles and most of those that have been studied are NiAs-related structures. Here, we show that a high-entropy skutterudite-type intermetallic compound, (CoNiRhIrRu)Sb₃, can be synthesized as colloidal nanoparticles by slowly injecting a solution containing a mixture of all constituent metal salts into a heated solvent. Time-point studies suggest that nanoparticles of elemental antimony form first, followed rapidly by the galvanically triggered formation of (CoNiRhIrRu)Sb₃. The formation of (CoNiRhIrRu)Sb₃ is especially notable because among the binary skutterudite end members, only IrSb₃ forms under the same reaction conditions and NiSb₃ and RuSb₃ are metastable phases that have not previously been reported as nanoparticles. Given their constituent elements, the (CoNiRhIrRu)Sb₃ nanoparticles were screened for catalytic viability for the hydrogen evolution and oxygen evolution reactions in acidic and alkaline electrolytes.