Palladium-copper alloys as catalysts for the oxygen reduction reaction in an acidic media I: Correlation between the ORR kinetic parameters and intrinsic physical properties of the alloys

The oxygen reduction reaction (ORR) on Pd-Cu catalyst has been studied in acidic media. The palladium alloys were prepared by coating glassy (GC) carbon substrates using a R-F magnetron sputtering equipment with a palladium and a copper wafer as targets. The dual sputtering we used has allowed us to obtain a thin film of 1 mu m thick. The ORR kinetics was studied on these catalysts in 0.1 M HClO4. Cyclic voltammetry (CV) was used to determine the electrochemical surface area (S-el). An increase in S-el with the Cu content in the alloy was observed for the alloys containing less than 50% in Cu while a constant value of 23 cm(2) is reached after this content in Cu. It was further shown that the ORR on the Pd-Cu alloys proceeds through four transferred electrons mechanism and a Tafel slope of 60 mV/dec at low over potentials. The Pd50Cu50 exhibits the highest activity for this reaction. The enhancement of the electro catalytic activity is attributed to an optimal d band property that makes easier the OOH dissociative adsorption which is considered as chemical rate determining step (RDS) for the ORR. (C) 2009 Elsevier B.V. All rights reserved.