High-performance PtCu_x at Pt core-shell nanoparticles decorated with nanoporous Pt surfaces for oxygen reduction reaction

PtCu_x at Pt/C (x = 3, 5, and 7) core-shell catalysts with nanoporous Pt surfaces were synthesized via the galvanic replacement reaction. The surface morphology and elemental compositions of the PtCu_x at Pt/C catalysts were significantly influenced by the initial ratio of Cu to Pt in the PtCu_x nanoparticle substrates, and porous surfaces on the PtCu_x at Pt nanoparticles could be produced when the Cu to Pt ratios in the PtCu_x nanoparticle substrates were greater than 5. In addition, the nanoporous PtCu_x at Pt nanoparticles showed different electronic structures depending on the surface to bulk compositions. Therefore, the oxygen reduction reaction (ORR) activities of the PtCu_x at Pt/C catalysts were significantly influenced by the surface morphologies and atomic ratios of Cu to Pt near the surface of the nanoparticles. Among the PtCu_x at Pt/C catalysts synthesized, PtCu₇ at Pt/C catalyst with a nanoporous Pt surface exhibited superior ORR activity and durability compared to a commercially available Pt/C JM catalyst. The d-band downshift of the PtCu₇ at Pt/C catalyst by the formation of highly porous Pt layers on the Cu-enriched subsurface layer resulted in the enhancement of the catalytic activity and durability for the ORR. High durability of the PtCu₇ at Pt/C catalyst was attributed mainly to the increase in the dissolution potential of the Pt surface layers on the Cu-enriched subsurface layer. The Cu dissolution from the subsurface regions of the nanoparticles was also considerably retarded, owing to the surface protection offered by stable Pt shell layers.