Bimetallic catalysts for ORR and EOR

Actually platinum is still the most common metal catalyst in both anode and cathode fuel cell. In spite of the many attempts made in the last decade to develop non-Pt based catalysts for low temperature air cathodes, Pt remains the catalyst of choice, at least for acid based fuel cells. The situation in alkaline electrolytes is rather different; due to the stability of non-noble metals in this environment, many more opportunities are available for the development of non-Pt catalysts for the Oxygen Reduction Reaction (ORR) and for the Ethanol Oxidation Reaction (EOR). To completely remove Pt and to replace it with less expensive materials, bimetallic electrocatalysts have been proposed to exploit a synergic mechanism with one metal able to break the O-O bond of the molecular oxygen at the cathode side and the second metal effective in reducing the adsorbed oxygen so formed [1]. At the same time the Pd-based catalysts in alkaline-type DEFCs can be an alternative to the Pt-based catalysts for the alcohol oxidation reactions in alkaline media [2]. In this contest we studied the contribution of two binary catalyst against the ORR and EOR: Silver and cobalt, whose catalytic activity against the ORR have been reported long ago [3- 5] were combined together by electrodeposition on a glassy carbon electrode. The activity of the small amount of the binary Ag-Co catalyst (17 g cm-2) were compared with the catalytic activity of the only-silver deposits that had given the best catalytic effect in Ref 6. Rotating ring electrode measurements were performed to estimate the average number of exchanged electron during the reaction. On the other hand the catalytic activity of a Pd-Co alloy against the EOR was estimated. The Pd-Co samples were grown by co-deposition on a Si/Au electrode and the increasing amount of Co was correlated with the increasing catalytic propriety of the samples. An unusual change of the morphology on the Co-rich sample was observed during the cyclic voltammetry study due to a partial dissolution and deposition of the same metal..