Abstract
We report the top-down modification of intermetallic platinum-cobalt (Pt-Co) nanoparticle catalyst with molybdenum (Mo) promoters that significantly enhance its oxygen reduction activity. With an optimized coverage of the Mo promoters, X-ray absorption spectroscopy reveals the cluster-like Mo species effectively weakened the binding affinity of Pt surfaces towards oxygen. The Mo-promoted intermetallic Pt-Co catalyst thus exhibits high ORR mass activity of 0.89 A/mg_(Pt) compared to 0.22 A/mg_(Pt) and 0.62 A/mg_(Pt) for pure Pt and Pt-Co respectively under rotating disk electrode testing conditions. The high ORR activity further enabled the operation of the fuel cell membrane electrodes under low cathode relative humidities with minimal penalties in ionic transport resistance at low current regions. Density functional theory calculations reveal the beneficial role of molybdenum oxide cluster species in lowering the d-band energy surface Pt atoms, particularly at Pt segregated regions with no Pt-Co phase in proximity to induce the strain or ligand effects.
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