Electrocatalytic properties of Co, Pt, and Pt-Co on carbon for the reduction of oxygen in alkaline fuel cells

The effect of cobalt, platinum, and cobalt-platinum, alloys on high surface area carbons for oxygen reduction in alkaline electrolyte was investigated. The Pt-Co catalyst with ca. 1:3 atomic ratio was prepared by addition of H2PtCl6 solution to a mixture of methanol and a 5% surfactant in deionized water containing cobalt acetate and carbon suspension. This was followed by drying and heat-treatment at 700 and 900 degrees C in a flow of hydrogen and nitrogen gas mixtures. Polarization curves and kinetic parameters for Pt, Co, and Pt-Co were conducted and compared in 6 M KOH and at 80 degrees C. Higher activities were observed for the Pt-Co alloy, that had been heat treated at 900 degrees C. In addition to increased activity of this catalyst, the unalloyed base metal (Co) contributes to total performance improvement of the oxygen reduction process. Furthermore, surface, structural, and chemical characterizations of the catalysts were carried out using transmission electron microscopy, x-ray diffraction, Brunauer, Emmett, and Teller method, and atomic absorption spectroscopy. Dissolution of cobalt from the electrodes, both from the single cobalt phase and Pt-Co alloy catalysts, has been established. The x-ray results demonstrated a shift to lower lattice parameters (3.618 Angstrom) by the Pt-Co alloys, prepared at 900 degrees C, than the pure platinum catalyst (3.919 Angstrom).