Electrochemical investigation of Pd-Co thin films binary alloy for the oxygen reduction reaction in acid medium

The oxygen reduction reaction (ORR) on Pd-Co electro-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 cobalt wafers as targets. The dual sputtering allowed us to obtain a thin film of 40-60 nm thick. The ORR kinetics was studied on these catalysts in 0.05 M H2SO4. An increase in the hydrogen adsorption charge, the oxide formation and the oxide reduction or desorption was observed with the Co content in the alloy for the alloys containing 20-84% of Co. It was further shown that the ORR on Pd-Co alloys proceeds through four transferred electrons mechanism and a Tafel slope of 60 mV/dec. The electro catalytic performance of the ORR on the various electrodes studied here is: in the order Pd16Co84 < Pd42Co58 < Pd < Pd50Co50 < Pd75Co25 < Pd65Co35 < Pt. This result clearly shows that alloying Pd with a specific composition of Co enhances significantly the electro-catalytic properties of the ORR on Pd-Co alloys in comparison to Pd alone. 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.