Revealing Robust Atomic Configurations of the Ligand-Assisted Synthesized High-Entropy PtIrFeCoNiCu...

Despite excellent catalytic performance via the "cocktail effect" and the phase stability of high-entropy alloys (HEAs), their multicomponent surface remains inadequately explored after oxygen reduction reaction (ORR). Moreover, the facile synthesis of nano HEAs is required for practical applications. Herein, nanosized (∼4.8 nm) carbon-supported PtIrFeCoNiCu intermetallics (PtIr-iHEA/C), ∼90% ordered, are prepared through a mercaptosuccinic acid (MSA)-assisted strategy. Combining atomic-level characterizations and theoretical calculations, the activity is correlated with the evolving surface configuration. Leveraging the activated Pt and Fe sites, PtIr-iHEA/C displays an initial mass activity (MA) of 1.65 A mg_Pt/Ir ^-1 (0.90 V vs RHE) in rotating disk electrodes (6.9 times that of Pt/C), notably with negligible E_1/2 degradation after 50 000 potential cycles. However, post-characterizations suggest the cycling induces transition metal (TM) leaching, reconstructing the PtIr-iHEA@Pt core-shell structure. Theoretical analysis attributes the durable performance tothe electronically optimized rigid Pt shell (active sites) and the strain-anchored sublayer TMs. Consequently, the fuel cell incorporating PtIr-iHEA@Pt/C delivers a high mass-normalized peak power density of 11.6 W mg_Pt/Ir ^-1 (H₂/Air), and 79% MA retention from 0.75 A mg_Pt/Ir ^-1 after cycling (DOE targets: 0.44 A mg_Pt ^-1, 60% retention). This study uncovers structure-performance correlations of Pt-based iHEA for acidic ORR, enlightening the rational HEA design for broader applications.