Single-nanometer-scale Pt–Si fine particles (Pt–Si NPs) were synthesized via the arc-plasma deposition of Si on a highly oriented pyrolytic graphite at a fixed substrate temperature of 600 °C, followed by electron-beam deposition of Pt at the temperatures between 100 and 600 °C in ultra-high vacuum. X-ray diffraction patterns of the vacuum-synthesized Pt–Si NPs showed that a solid solution of Pt–Si was the major component of the particles. Minor diffraction peaks, due to the intermetallic compounds (Pt3Si1 and Pt12Si5), at the Pt-deposition temperature (Tsub-Pt) of 500 °C, were also observed. Scanning tunneling microscopic images exhibited that Pt–Si NPs with an average diameter less than 10 nm were dispersed in the substrate at Tsub-Pt temperatures up to 500 °C. The Pt–Si NPs synthesized at a Tsub-Pt of 300 and 450 °C showed 1.7 times higher initial mass activity for oxygen reduction reaction (ORR) compared to commercial carbon-supported Pt NPs catalysts and showed better electrochemical stability than pure Pt NPs. These results demonstrate that the arc-plasma deposition of Si NPs, followed by e-beam deposition of metal elements (Pt) in ultra-high vacuum is a new class dry-synthesis for the single-nanometer-scale fine particles of Pt–Si for electrocatalysis, e.g. ORR.
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