High-Index Core-Shell Ni-Pt Nanoparticles as Oxygen Reduction Electrocatalysts

Developing solid solution nanoparticles with complex faceted geometries and unusual composition sectoral zoning can enhance their catalytic performance. In a solution-phase synthesis of PtNi nanoparticles, we show that a mixture of surfactants results in surface functionalization, which in turn controls the morphological evolution of nanoparticles. The nanoparticles exhibited complex chemical growth zoning, rich in Pt geometric topologies, which varied as a function of surfactant mixture. Compositional mapping, using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) coupled with energy dispersive X-ray spectroscopy (EDS), highlights core-shell structures (similar to 1 nm Pt coating thickness) with edge-vertex Pt-enrichment and Ni-rich faces. These core-shell Ni-Pt nanoparticles demonstrated enhanced activities toward the oxygen reduction reaction (ORR) compared to commercial Pt/C, even after extended potential cycles (5000). Our synthetic approach, which utilizes the surfactants' array of distinct functional groups, offers new avenues toward the formation of concentric core-shell structures with multifaceted topologies. These materials show considerable promise as electrocatalysts.