The preparation and characterization of platinum based electrocatalysts for methanol oxidation in fuel cells

Novel bimetallic Pr/Fe colloidal particles were prepared using iron oxide colloidal particles as seed sols and platinum oxides were grown on them. Bimetallic Pt/Ru colloidal particles were made with the method developed by Watanabe. By using Vulcan XC-72 carbon black as supports, bimetallic electrocatalysts of Pt/Ru/C and Pt/Fe/C for methanol electrochemical oxidation in fuel cells were synthesized. Electrochemical measurements of the Pt/Fe/C colloidal particles as electrocatalyst for methanol oxidation demonstrated that this catalyst has much higher electrochemical efficiency than conventional Pt catalyst.; By using transmission electron microscopy (TEM) and energy dispersive x-ray spectroscopy (EDXS), effects of different preparation conditions including reaction time, sequence of adding chemicals and metal oxide particle size on the generation of the metal oxide colloidal particles and the formation of bimetallic colloidal particles were investigated. It has been demonstrated that: (1) The sizes of platinum and platinum oxide colloidal particles were controlled by the reaction time after the addition of {dollar}rm Hsb2Osb2{dollar} into the platinum complex solution; (2) The sequence of adding chemicals ({dollar}rm Hsb2Osb2{dollar} and iron oxide colloidal particles) was critical for the formation of Pt/Fe bimetallic particles; and (3) The reaction time for the formation of platinum oxide colloidal particles greatly influenced the particle size, chemical composition and crystal structure of the Pt/Ru bimetallic products.; The electrochemical efficiencies for methanol oxidation of the Pt/Fe/C catalysts were determined by cyclic voltammetry. No obvious difference was observed between the Pt/Fe/C catalysts with and without hydrogen bubbling treatment during the preparation. For the Pt/Fe/C catalysts prepared with 2 h and 24 h reaction time, a higher electrochemical efficiency was observed for the catalyst with 24 h reaction time. Introduction of iron oxide particles before the addition of {dollar}rm Hsb2Osb2{dollar} in the preparation of Pt/Fe/C catalysts resulted in a higher electrochemical efficiency. Study of the durability of the Pt/Fe/C catalysts indicated that good electrochemical efficiencies were recorded up to the third runs. Two electrolyte solutions, 0.1 M {dollar}rm Hsb2SOsb4{dollar} and 0.1 M HClO{dollar}sb4{dollar}, were used to compare the catalytic activities of the catalysts. No significant difference was observed between these two electrolyte solutions. For increasingly higher methanol concentrations (up to 4 M), higher oxidation potentials were observed for methanol electrochemical oxidation, as well as higher current efficiencies of the Pt/Fe/C catalysts. Multiple scan effects were measured and discussed. The electrochemical efficiencies of the Pt/Fe/C catalyst prepared by introducing iron oxide particles prior to the addition of {dollar}rm Hsb2Osb2{dollar} increased to a maximum after several potentiodynamic cycles, and then dropped. For the catalyst prepared by adding {dollar}rmsb Hsb2Osb2{dollar} before introducing iron oxide, the electrochemical efficiencies of the catalyst increased in terms of increased dissolution of the iron oxide. There was no significant improvement in electrochemical efficiencies by treating the Pt/Fe/C catalysts with hydrogen bubbling. (Abstract shortened by UMI.)...