Heat-treatment-induced enhancement of activity and stability in Rh/Mo-doped PtNi octahedra for the oxygen reduction reaction

Platinum-based bi- and trimetallic octahedral nanoparticles are among the most promising catalysts for the oxygen reduction reaction (ORR) at the cathode of proton exchange membrane fuel cells (PEMFCs). While these catalysts already exhibit excellent activity, their performance and durability can be significantly enhanced through reductive heat treatment and controlled doping. In this study, we investigate the structural and electrochemical evolution of Ni-rich PtNi and Mo/Rh-doped PtNi octahedra subjected to heat treatment in a hydrogen atmosphere. Rotating disk electrode (RDE) measurements reveal substantial improvements in both specific activity and long-term stability for the doped, heat-treated catalysts. Identical location scanning transmission electron microscopy (IL-STEM) confirms the exceptional morphological stability under accelerated aging conditions. <i>In situ</i> X-ray diffraction (XRD) and environmental STEM analyses attribute the enhanced performance to the formation of a thermodynamically stabilised Pt-rich skin. These findings highlight the dual role of dopants in preserving the active morphology and promoting beneficial surface segregation, offering valuable insights for the rational design of next-generation ORR catalysts for PEMFCs.