Tailoring Interfacial Oxygen Vacancy‐Mediated Ordering in Ternary Pt ₃ (Co,Mn) ₁ Intermetallic Nanoparticles for Enhanced Oxygen Reduction Reaction

ABSTRACT The sluggish kinetics and limited durability of the oxygen reduction reaction (ORR) at the cathode remain a major barrier to the widespread deployment of proton exchange membrane fuel cells (PEMFCs). Here, we introduce a low‐temperature interfacial engineering strategy to construct ternary L1 2 ‐ordered Pt 3 (Co,Mn) 1 intermetallic nanoparticles. A conformal MnO shell on Pt 3 Co 1 cores not only suppresses particle coalescence but also undergoes redox activation to generate interfacial oxygen vacancies that initiate the disorder‐to‐order transition. During thermal activation, these vacancies mediate Co–Mn atomic exchange across the core@shell interface, forming interfacial Co–O and intralattice Pt–Mn bonds that cooperatively stabilize the ordered framework. This oxygen‐vacancy‐driven interfacial evolution reconfigures the Pt electronic structure, downshifting the d‐band center, enriching electron density at Pt active sites, and optimizing oxygen‐intermediate adsorption. The resulting catalyst exhibits high intrinsic ORR activity and outstanding durability over extended accelerated cycling. When implemented into practical membrane‐electrode assemblies, it surpasses the U.S. Department of Energy (DOE) 2025 PEMFC benchmarks for both rated power density and durability, demonstrating its promise for real‐world fuel cell applications. More broadly, this work establishes redox‐active, confinement‐mediated interfacial engineering as a general paradigm for directing atomic ordering and electronic structure in complex multimetallic electrocatalysts.