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

Abstract

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.