Directional f-d Orbital Coupling as a Key Electronic Factor for Enhanced Oxygen Reduction Reaction in Pt-based Core-Shell Catalysts.

Abstract

The intensity and spatial ordering of f-d orbital coupling in platinum-rare earth (Pt-RE) intermetallic compounds represent an important factor for the oxygen reduction reaction (ORR). Using a Pt5Ce@Pt core-shell model, we engineer two distinct structures: ordered s-Pt5Ce@Pt with expected strong directional f-d coupling, and disordered w-Pt5Ce@Pt with weak localized coupling. Despite similar Pt shell thicknesses, the ordered core confines Ce uniformly within the interior, whereas the disordered counterpart exhibits uneven Ce distribution and partial diffusion into the shell. The periodic ordered lattice enables maximized Ce 4f-Pt 5d orbital overlap, which drives efficient electron transfer, modulating the Pt d-band-center position toward a more favorable range, strengthening Pt-Ce bonds, and effectively suppressing Pt dissolution and Ostwald ripening. Consequently, s-Pt5Ce@Pt delivers a mass activity of 0.8 A mgPt -1 and achieves a 13% increase after 30k cycles in acidic media. Post-cycling characterizations reveal partial selective dissolution of subsurface Ce atoms, which is expected to sustain the near-surface compressive-strain field and contribute to catalyst durability. This work reveals a qualitative correlation between atomic-ordering-mediated Pt-Ce electronic interaction and ORR performance for high-performance Pt-RE catalysts and offers new insights into the structural evolution of intermetallic compounds under harsh electrochemical conditions.

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