Thanks to their remarkably high activity towards ORR platinum-based octahedrally shaped nanoparticles have attracted ever increasing attention in last years. Although high activities for ORR catalysts have been attained, the practical use is still limited by their long-term stability. In this work, we present Rh-doped Pt-Ni octahedral nanoparticles with high activities up to 1.14 A mgPt-1 combined with improved performance and shape stability compared to previous bimetallic Pt-Ni octahedral particles. The synthesis, the electrocatalytic performance of the particles towards ORR and atomic degradation mechanisms are investigated with a major focus on a deeper understanding of strategies to stabilize morphological particle shape and consequently their performance. Rh surface doped octahedral Pt-Ni particles were prepared at various Rh levels. At and above about 3 at.% the nanoparticles maintained their octahedral shape even past 30,000 potential cycles, while undoped bimetallic reference nanoparticles show a complete loss in octahedral shape already after 8,000 cycles in the same potential window. Detailed atomic insight in these observations is obtained from aberration-corrected scanning transmission electron microscopy (STEM) and energy dispersive X-ray (EDX) analysis. Our analysis shows that it is the migration of Pt surface atoms, not - as commonly thought - the dissolution of Ni that constitutes the primary origin of the octahedral shape loss for Pt-Ni nanoparticles. Using small amounts of Rh we were able to suppress the migration rate of platinum atoms and consequently suppress the octahedral shape loss of Pt-Ni nanoparticles.