The carbon supported PtFeS catalysts were prepared by a modified polyol method. In brief, 0.3 g carbon (Ketjen-black heat-treated at 2250 °C, SE = 160 m2 g-1) was dispersed in 135 g ethylene glycol. 5.993 g of 8 wt% H2PtCl6 (Umicore; Pt content, 39.8 wt%), 1.874 g of 8 wt% FeCl3. 6H2O (Sigma-Aldrich), and 0.352 g of 8 wt% (NH2)2SC (Sigma-Aldrich) previously mixed in ethylene glycol were added to the dispersion. The pH of the stirred reaction mixture was adjusted to ∼11 using 1 M NaOH dissolved in ethylene glycol. Then, 2.095 g of 50 wt% H2NaPO2.H2O and 1.57 g of 20 wt% hydrazine were added to the reaction mixture. The resulting mixtures were reduced in a microwave reactor at 250 °C for ∼1 h. The reduced resulting product was washed with deionized
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3a–b. All the catalyst nanoparticles are uniformly distributed on the carbon support with a graphitic layer. Although the average particle size of Pt and PtFeS catalysts, obtained from more than 20 nanoparticles in their corresponding TEM images, is 3.12 and 3.37 nm, respectively, a clear difference in the morphology was observed. The TEM image of Pt catalyst shows spherical shaped Pt nanoparticles, in contrast to PtFeS catalyst exhibiting a mixture of spherical and rod-like morphology. The rod-typed morphology observed in the PtFeS catalyst indicates that nanoparticles are horizontally overgrown at the edge of preformed nanoparticles by the decomposition of thiol compound. The mapping of the electron energy-loss spectroscopy (EELS) using a scanning transmission electron microscope (STEM) was performed to reveal the distribution of Pt, Fe, and S elements in a representative single nanoparticle of the PtFeS catalyst as shown in Fig. 3c. Overlapping the mapping of Pt, Fe, and S EEL signals from a single nanoparticle validates the core–shell structure, indicating the formation of sulfur and iron atom-rich core and Pt-rich shell. Those structures could form more favorable compressive strain on Pt because of the contraction by binary alloy of Fe and S in the core. The apparent positive effect of PtFeS core–shell structure enables convenient tuning of the geometric properties of Pt in the alloy
3a–b. All the catalyst nanoparticles are uniformly distributed on the carbon support with a graphitic layer. Although the average particle size of Pt and PtFeS catalysts, obtained from more than 20 nanoparticles in their corresponding TEM images, is 3.12 and 3.37 nm, respectively, a clear difference in the morphology was observed. The TEM image of Pt catalyst shows spherical shaped Pt nanoparticles, in contrast to PtFeS catalyst exhibiting a mixture of spherical and rod-like morphology. The rod-typed morphology observed in the PtFeS catalyst indicates that nanoparticles are horizontally overgrown at the edge of preformed nanoparticles by the decomposition of thiol compound. The mapping of the electron energy-loss spectroscopy (EELS) using a scanning transmission electron microscope (STEM) was performed to reveal the distribution of Pt, Fe, and S elements in a representative single nanoparticle of the PtFeS catalyst as shown in Fig. 3c. Overlapping the mapping of Pt, Fe, and S EEL signals from a single nanoparticle validates the core–shell structure, indicating the formation of sulfur and iron atom-rich core and Pt-rich shell. Those structures could form more favorable compressive strain on Pt because of the contraction by binary alloy of Fe and S in the core. The apparent positive effect of PtFeS core–shell structure enables convenient tuning of the geometric properties of Pt in the alloy