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 μm 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 (Sel). An increase in Sel with the Cu content in the alloy was observed for the alloys containing less than 50% in Cu while a constant value of 23 cm2 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.