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

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 L1₂-ordered Pt₃(Co,Mn)₁ intermetallic nanoparticles. A conformal MnO shell on Pt₃Co₁ 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.