454 453 462 466 470 474 Binding Energy/eV

454 453 462 466 470 474 Binding Energy/eV

Binding Energy / eV

Fig. 2a-b. X-ray photoclcctron spcctra of the Pt-Ru/C catalyst

SEA f-EDAX analysis. — The "paste process" method introduces new features with respcct to the conventional procedures employed in the realization of a M&E assembly. In the present assembly the ionomer is distributed through the overall catalyst region. As opposite, in the conventional method, the ionomer is localized at the clcctrode - electrolyte interface. It is pointed out that the colloidal ionomer chains, in the "paste process", establish links between catalyst particles improving the structural integrity of the catalyst layer and supplying a net- work for proton conduction. Microprobe analysis was carricd out on various portions of the catalyst layers. The relative intensities of platinum and sulfur signals did not significantly change along the catalyst layers accounting for a homogeneous distribution of the ionomer in the two catalysts. It is observed that the "paste process" preparation method allows a significant increase of the three-phase reaction zone at the clectrode-electrolyte interface. Electrochemical analysis. —Fig. 3 shows a comparison of the galvanostatic polarization data with 2 M and 1.5 M methanol concentration together with the corresponding power density curves obtained upon correction for ohmic drop (0.22 ohm cm2). It can be observed that the open circuit potential is close to 0.9 V. Significant potential losses are observed in the activation and diffusion controlled regions of the polarization curves. At low current densities, a sudden decrease of about 0.2 V of ccll potential is recorded when a slight current is allowed to pass through the ccll (Fig. 3). The polarization curve obtained in 1.5 M methanol solution showed a lower deactivation at intermediate currents. Power densities of about 150 mW cm"2 are obtained at 95 °C with low Pi loadings in the electrodes.

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