ABSTRACT
Here, we study the influence of the Pt loading and the particle size of Pb0.25@Ptx/C catalysts on their specific activity toward ethanol oxidation in acid media. High angle annular dark field-scanning transmission electron microscopy and electron energy loss spectroscopy data indicate the formation of Pb0.25@Ptx/C core-shell structures, which are well dispersed on carbon support, with spherical shapes and small particle sizes (2.9-6.6 nm). Cyclic voltammetry experiments confirm characteristic profiles of polycrystalline Pt for Pb0.25@Ptx/C structures. The specific activity of the catalysts toward ethanol oxidation reaction greatly depends on the Pt content on Pb core, and consequently, depends on the size of the nanoparticles. The optimum activity occurs with the lowest Pt load in the shell and smaller particle size. Enhancements in specific activity result from the higher number of nanoparticles available for the ethanol oxidation reaction and the tensile strain effect of Pt atoms on the surface expanded in Pb0.25@Pt0.75/C. The lower activity observed for the catalysts with loads of 35 and 50% wt. (Pb0.25@Pt1.5 and Pb0.25@Pt2.25/C, respectively) in comparison to Pt/C, could be explain by the larger particle sizes obtained at these catalysts. Moreover, the Pb0.25@Pt0.75/C catalyst has high electrochemical stability and should be more stable in direct ethanol fuel cells systems than monolithic Pt catalysts. This is because the Pt shell in Pb0.25@Pt0.75/C exhibits lower chemical potential (p < 0) than at Pt/C and at the other core-shell catalysts studied; thus, reducing its tendency to dissolve. The developed core-shell nanostructure is thus a potential candidate as high-performance anode catalyst for application in direct ethanol fuel cells.
