Platinum-free electrocatalysts for oxygen reduction reaction

Platinum and Pt-alloys are at present the best catalysts for oxygen reduction in PEM fuel cells. Since the precious metal is scarce and expensive, there is a strong effort to find substitute catalysts. Catalysts based on iron and cobalt ions seem to be a good and promising alternative to platinum. Moreover, the nature and behaviour of the catalyst support are also of the utmost importance. Activated carbons are used as catalyst and electrocatalyst supports in many chemical and electrochemical processes. This is due to the fact that through their structural and morphological features (high surface area, controlled porosity with selected pore size dimensions, high adsorption power and complex surface chemistry) they generally improve the intrinsic catalyst behavior. Improved performances of such composite catalyst-substrate materials are desirable and can be obtained by modifying the nature and number of the native functional groups of the carbon surface and by introducing new surface species, as metal centres, heteroatoms, etc.. In this work we present some data concerning electrochemical oxygen reduction onto nitrogen-modified activated carbon also bearing transition metal cations. Different nitrogen-bearing precursors and carbon sources will be considered. Catalysts characterisation was carried out by physical, chemical and electrochemical methods. Results are given in terms of the influence that nitrogen and carbon precursors exert on the electrocatalytic activity of the obtained materials.