Influence of Sn content on PtSn/C catalysts for electrooxidation of C1-C3 alcohols:: Synthesis, characterization, and electrocatalytic activity

A series of carbon-supported bimetallic PtSn catalysts for the electrooxidation of C-1-C-3 alcohols (i.e., methanol (C-1), ethanol (C-2), and 1-propanol (CO) were prepared with different Pt:Sn atomic ratios using borohydride reduction method combined with freeze-drying procedure at room temperature. The catalysts were investigated by employing various physicochemical analyses: X-ray diffraction (XRD), transmission electron microscopy (TEM) and extended X-ray absorption fine structure (EXAFS) to investigate the structural modification, and X-ray photoelectron spectroscopy (XPS) and X-ray absorption- near-edge spectroscopy (XANES) to characterize the change in electronic features. The variation of Sn content by forming PtSn alloys causes significant structural and electronic modifications of Pt crystallites, resulting in increases of lattice parameter and decreases of the Pt 5d band vacancies with Sn content. Cyclic voltammetry (CV) measurements showed that the addition of Sn into the Ptcatalyst promotes the electro-catalytic activities for the electrooxidations of C-1, C-2, and C-3 alcohols, in which the maximum activities appeared at different Sn contents for the C-1-C-3 alcohols. In particular, a shift in optimum Pt:Sn composition was observed in that the Sn content required to reach the maximum peak current density was increased with the increasing number of carbon atoms in the C-1-C-3 alcohols. Both the geometric and electronic effects with variation of Sn content are in close relationship in the bimetallic PtSn catalysts, consequently affecting the electrocatalytic activities by showing volcano-type behaviors over the electrooxidation of the individual alcohol. (C) 2008 Elsevier B.V. All rights reserved.