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Refined Structural Analysis of Connected Platinum–Iron Nanoparticle Catalysts with Enhanced Oxygen Reduction Activity

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journal contribution
posted on 30.01.2018, 00:00 by Hidenori Kuroki, Takanori Tamaki, Masashi Matsumoto, Masazumi Arao, Yohei Takahashi, Hideto Imai, Yoshitaka Kitamoto, Takeo Yamaguchi
Carbon-free connected Pt–Fe nanoparticle catalysts exhibit excellent oxygen reduction reaction (ORR) activity. Unlike conventional ORR catalysts, connected Pt–Fe catalysts comprise a beaded network structure formed by the connection of Pt–Fe nanoparticles. The refined structural analyses reveal that the connected Pt–Fe network comprises a polycrystalline structure, whereas the commercial Pt nanoparticle on carbon is formed by a single crystal. In addition, a Pt-rich thin layer made of three-to-four platinum atomic layers with high-index stepped facets was observed on the catalyst surface in the connected Pt–Fe catalyst after electrochemical treatment in an acid electrolyte. Lattice spacing analysis showed that the Pt–Pt bond distance in the Pt-rich surface layer is longer than that inside the network of Pt–Fe alloys. Such surface structures play a beneficial role in enhancing ORR activities. The obtained results provide guidelines for catalyst structural designs that can improve ORR activity.