Carbon supported Pt-Au catalysts with different bimetallic compositions were prepared by water in oil (w/o) microemulsion. Carbon Vulcan XC-72 was added during the synthesis of particles in order to obtain their good dispersion and a mean particle size distribution of 5.02 +/- 0.56 nm. Structural characterization was performed using XRD at wide angles (WAXS), which showed that Pt-Au particles exhibited alloy properties. Electrochemical characterization allowed to estimate the surface composition of Pt-Au alloys, which was close to that of the bulk material Pt(20)Au(80). This catalyst composition displayed the best catalytic activity in steady-state conditions in comparison with Pt(50)Au(50) or Pt and Au alone. Moreover, a Pt-Au/C catalyst with a metal loading of 40 wt % was immobilized onto a carbon porous tube as anode. A membrane-less biofuel cell was tested using laccase/ABTS biocathode in phosphate buffer (pH 5).
The electrooxidation of DME was studied at a bulk platinum electrode. It was shown that the DME adsorption was a slow step in the overall oxidation reaction. The DME adsorption is potential dependent in the hydrogen region of platinum and independent in the double layer region. From low potential scan rate voltammetry and DME stripping experiments, it was shown that the DME oxidation mechanism occurred via several reaction paths. At low potentials, DME oxidation leads to the existence of a positive current plateau. ''In situ'' Infrared Reflectance Spectroscopy experiments were carried out to identify the intermediate and reaction products of DME adsorption and oxidation at different potentials. CO L (linearly bonded CO), CO B (bridge bonded CO), adsorbed COOH species and CO 2 were detected. From these electrochemical and spectro-electrochemical results, it was proposed that some adsorbed DME was hydrolysed and directly oxidized to CO 2 or HCOOH species and some partially blocked platinum sites at the surface forming Pt-CHO and/or Pt-CO. Then, as soon as platinum becomes able to activate water, a bifunctionnal mechanism occurs to form either HCOOH or CO 2 again following two different reaction paths.
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