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Pt-based intermetallics are expected to be the highly active catalysts for oxygen reduction reaction (ORR) in proton-exchange membrane fuel cells but still face great challenges in controllable synthesis of interatomically ordered and ultrafine intermetallic nanoparticles. Here, we propose an oxygen vacancy-mediated atomic diffusion strategy by mechanical alloying to reduce the energy barrier of the transition from interatomic disordering to ordering, and to resist interparticulate sintering via strong M-O-C bonding. This synthesis results in a nanosized core/shell structure featuring an interatomically ordered PtM core and a Pt shell of two to three atomic layers in thickness and can be extended to the multicomponent PtM (M = Co, FeCo, FeCoNi, FeCoNiGa) systems. The electron enrichment in the Pt outer shell induced by the compressive strain leads to the enhanced antibonding orbital occupation below the Fermi level and accelerated OH* desorption kinetics. The optimized PtCo-O/C-6 catalyst presents excellent ORR activity (mass activity = 1.28 A mgPt-1 at 0.9 ViR-free, peak power densities = 2.38/1.25 W cm-2 in H2-O2/-air) and durability (∼1% activity loss in over 50 h in air condition) in fuel cells at a total Pt loading of 0.1 mgPt cm-2. Furthermore, we establish a systematic correlation to elucidate the formation mechanisms of highly ordered intermetallic catalysts underlying oxygen vacancies. This study provides a general approach for the large-scale production of highly ordered and nanosized Pt-dispersed intermetallic catalysts.
Kong et al. (Tue,) studied this question.