Sulfur-stabilized intermetallic nanoparticles: Nanoparticles of intermetallic alloys of platinum could have enhanced electronic properties that improve their catalytic activity, but the high temperatures needed to ensure complete atomic diffusion often lead to the growth of larger nanoparticles—sintering—with low surface area and hence low overall activity. Yang et al . show that sulfur-doped carbon supports create strong platinum-sulfur bonds that stabilize small platinum alloy nanoparticles (<5 nanometers in diameter) to temperatures up to 1000ºC. They screened libraries of platinum alloys and identified ones with high mass activity for the oxygen reduction reaction in hydrogen fuel cells. —PDS

Morphological shape in chemistry and biology owes its existence to anisotropic growth and is closely coupled to distinct functionality. Although much is known about the principal growth mechanisms of monometallic shaped nanocrystals, the anisotropic growth of shaped alloy nanocrystals is still poorly understood. Using aberration-corrected scanning transmission electron microscopy, we reveal an element-specific anisotropic growth mechanism of platinum (Pt) bimetallic nano-octahedra where compositional anisotropy couples to geometric anisotropy. A Pt-rich phase evolves into precursor nanohexapods, followed by a slower step-induced deposition of an M-rich (M = Ni, Co, etc.) phase at the concave hexapod surface forming the octahedral facets. Our finding explains earlier reports on unusual compositional segregations and chemical degradation pathways of bimetallic polyhedral catalysts and may aid rational synthesis of shaped alloy catalysts with desired compositional patterns and properties.