Pt and Pt-Ru catalysts for polymer electrolyte fuel cells deposited onto carbide derived carbon supports

This paper presents the behaviour of ordered micromesoporous tungsten carbide derived carbon supported catalysts as possible cathodes for polymer electrolyte membrane fuel cell (PEMFC). Tungsten carbide derived carbon (C(WC), specific surface area 2116 m(2) g(-1)) has been prepared at 1100 C using chlorination method. Pt and Pt-Ru alloy catalysts were deposited onto C(WC) with high dispersion, and particle size being approximately 2.1 nm for Pt-Ru and 7.4 nm for Pt. The loading of Pt nanoparticles and Pt-Ru alloy was 20 wt% (wt% is weight percent). Analysis of X-ray diffraction, X-ray fluorescence, transmission and high-resolution transmission electron microscopy, X-ray photoelectron and energy-dispersive X-ray spectroscopy data confirms that Pt-Ru alloy has been formed and the atomic fraction of Ru in the alloy is similar to 0.43. Cyclic voltammetry and rotating disc electrode data show that high cathodic oxygen reduction current densities (-150 Am-2 at 3000 rpm, calculated per flat cross-section surface area) have been achieved in 0.5M H2SO4 solution. The behaviour of the Pt-C(WC) and Pt-Ru-C(WC) catalysts has been determined by mixed kinetic processes within the electrode potential range from 0.1V to 0.3 V vs. MSE and the diffusion within the range from 0.1 V to -0.35V vs. MSE. The number of electrons transferred per electroreduction of one O-2 molecule (similar to 4) at Pt-C(WC), calculated from Levich plots, are in a good agreement with literature data. Analysis of impedance spectra for Pt-C(WC) and Pt-Ru-C(WC), similarly to Ru/RuO2 system in H2SO4 aqueous solution, the pseudocapacitive processes have been observed at very low ac frequencies, explained by cathodic hydrogen adsorption/desorption and very slow electrical double layer formation processes caused by adsorption of reaction intermediates at/inside micromesoporous Pt-C(WC) and Pt-Ru-C(WC) catalysts. Very high series and parallel capacitance values similar to 200 F g(-1) have been established at -0.51 V vs. MSE, attractive for hybrid aqueous supercapacitor applications. (C) 2012 Published by Elsevier Ltd.