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Carbon-supported Pt@Cu “core−shell” nanoparticles with Pt−Cu alloy core and Pt shell have been synthesized by a galvanic displacement of Cu by Pt4+ at ambient conditions, followed by a leaching out of unreacted Cu on the surface by treating with 9 M H2SO4. X-ray diffraction (XRD) data indicate the formation of a Pt−Cu alloy below the Pt shell. Energy dispersive spectroscopic (EDS) analysis in a scanning electron microscope (SEM) reveals that the experimental Cu content is much lower than the initial nominal Cu content, confirming the displacement of a significant amount of Cu by Pt. X-ray photoelectron spectroscopic (XPS) studies indicate surface enrichment by Pt. Cyclic voltammetry (CV) and rotating disk electrode (RDE) measurements demonstrate an enhanced catalytic activity for the oxygen reduction reaction (ORR) for optimum Pt@Cu compositions compared to that found with commercial Pt catalyst, both per unit mass of Pt and per unit active surface area basis. Moreover, the surface area specific activities of the Pt@Cu samples increase linearly with increasing initial nominal Cu content. The increase in activity for ORR is ascribed to an electronic modification of the outer Pt shell by the Pt−Cu core.

The formation of copper oxides and hydroxides from metallic copper and underpotentially deposited copper atoms on platinum nanoparticles, when it is subjected to a potential scan between the hydrogen evolution potential and the oxygen evolution potential in alkaline solution as a function of scan rate and the pH of the solution has been investigated. Cyclic voltammetry of bulk copper electrodes in alkaline solution reveal that oxidation proceeds in steps leading to formation of Cu 2 O, Cu(OH) 2 and CuO on the surface as well as some soluble oxides which corroborates well with X-ray photoelectron spectroscopy (XPS) analysis. Furthermore, interesting needle like formations on copper surface was observed in a scanning electron microscope (SEM), which can explain the unusual relation between the peak current and scan rate. On the other hand, the oxidation of copper monolayer on platinum nanoparticles leads primarily to formation of Cu 2 O and shows the effect of nobility imparted by the underlying platinum in terms of increased potential.

Carbon-supported Pd 100-x Mo x (0 e x e 40) nanoparticles have been synthesized by a simultaneous thermal decomposition of palladium acetylacetonate and molybdenum carbonyl in an organic solvent (o-xylene) in the presence of Vulcan XC-72R carbon, followed by heat treatment up to 900 °C in H 2 atmosphere and characterized chemically and structurally. X-ray diffraction data reveal the formation of single-phase facecentered cubic solid solutions for 0 e x e 30 after heat treating at 900 °C and the occurrence of a Mo 2 C impurity phase for x ) 40. The particle size of the Pd 100-x Mo x samples increase with increasing heat treatment temperature as revealed by transmission electron microscopy. Cyclic voltammetry (CV) and rotating disk electrode (RDE) measurements reveal that the alloying of Pd with Mo enhances the catalytic activity for the oxygen reduction reaction (ORR) as well as the stability (durability) of the electrocatalyst. However, the activity reaches a maximum at Pd 90 Mo 10 and then decreases with increasing Mo content. Similar observations are made in both single-cell proton-exchange membrane fuel cell (PEMFC) and direct methanol fuel cell (DMFC) for the ORR activity. Interestingly, the 900 °C Pd 90 Mo 10 exhibits catalytic activity for ORR in DMFC at 80 °C similar to that of as-synthesized Pt despite a significantly larger particle size due to a high tolerance of Pd 90 Mo 10 to methanol poisoning.

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