Assessing the roles of synthesis method and chemical composition in determining structure–property correlations in alloyed, ultrathin nanowire motifs for the methanol oxidation reaction

Abstract

In the context of developing novel fuel cell catalysts, we have successfully synthesized in high yields not only ultrathin nanowires with compositions of Pt₁Ru₁ and Pt₃Ru₁ but also more complex spoke-like dendritic clusters of Pt₁Ru₁ and Pt₁Ru₉ in ambient pressure under relatively straightforward, solution-based reaction conditions, mediated by either cetyltrimethylammonium bromide (CTAB) or oleylamine (OAm), respectively. EXAFS analysis allowed us to determine the homogeneity of the as-prepared samples. Based on this analysis, only the Pt₃Ru₁ sample was found to be relatively homogeneous. All of the other samples yielded results, suggestive of a tendency for the elements to segregate into clusters of ‘like’ atoms. We have also collected complementary HRTEM EDS mapping data, which support the idea of a segregation of elements consistent with the EXAFS results. We attribute the differences in the observed morphologies and elemental distributions within as-prepared samples to the presence of varying surfactants and heating environments, employed in these reactions. Methanol oxidation reaction (MOR) measurements indicated a correlation of specific activity (SA) values not only with intrinsic chemical composition and degree of alloying but also with the reaction process used to generate the nanoscale motifs in the first place. Specifically, the observed performance of samples tested decreased as a function of chemical composition (surfactant used in their synthesis), as follows: Pt₃Ru₁ (CTAB) > Pt₁Ru₁ (CTAB) > Pt₁Ru₁ (OAm) > Pt₁Ru₉ (OAm).