Electrochemical and physical characterization of Pt-Ru alloy catalyst deposited onto microporous-mesoporous carbon support derived from Mo2C at 600 °C

The electrochemical reduction of oxygen on binary Pt-Ru alloy deposited onto microporous-mesoporous carbon support was studied in 0.5 M H2SO4 solution using cyclic voltammetry, rotating disk electrode (RDE), and impedance method. The microporous-mesoporous carbon support C(Mo2C) with specific surface area of 1,990 m(2)g(-1) was prepared from Mo2C at 600 degrees C using the chlorination method. Analysis of X-ray diffraction, photoelectron spectroscopy, and high-resolution transmission electron microscopy data confirms that the Pt-Ru alloy has been formed and the atomic fraction of Ru in the alloy was similar to 0.5. High cathodic oxygen reduction current densities (-160 Am-2 at 3,000 revmin(-1)) have been measured by the RDE method. The O-2 diffusion constant (1.9 +/- 0.3x10(-5)cm(2)s(-1)) and the number of electrons transferred per electroreduction of one O-2 molecule (similar to 4), calculated from the Levich and Koutecky-Levich plots, are in agreement with literature data. Similarly to the Ru/RuO2 system in H2SO4 aqueous solution, nearly capacitive behavior was observed from impedance data at very low ac frequencies, explained by slow electrical double-layer formation limited by the adsorption of reaction intermediates and products into microporous-mesoporous Pt-Ru-C(Mo2C) catalyst. All results obtained for C(Mo2C) and Pt-Ru-C(Mo2C) electrodes have been compared with corresponding data for commercial carbon VULCAN (R) XC72 (C(Vulcan)) and Pt-Ru-C(Vulcan) electrodes processed and measured in the same experimental conditions. Higher activity for C(Mo2C) and Pt-Ru-C(Mo2C) has been demonstrated.