Comparison of the Activity of Pd-M (M: Ag, Co, Cu, Fe, Ni, Zn) Bimetallic Electrocatalysts for Oxygen Reduction Reaction

Carbon-supported 7.5 wt% Pd-2.5 wt% M (M: Ag, Co, Cu, Fe, Ni, Zn) bimetallic catalysts were synthesized via wet impregnation and assessed as electrocatalysts for the oxygen reduction reaction (ORR) in acidic solution at room temperature, using the thin-film rotating disk electrode technique. Monometallic 10 wt% Pt/C and 10 wt% Pd/C catalysts, prepared via the same method, were used as reference materials. The highest activity for ORR among the tested electrocatalysts was exhibited by PdZn/C and the lowest by Pd/C and PdCu/C. The activity of the rest Pd-based electrocatalysts followed the descending order: PdNi/C > PdAg/C >= PdCo/C > PdFe/C. The specific activity of PdZn/C was higher than that of Pt/C (more than 3 times higher for potentials 0.35-0.5 V versus Ag/AgCl), whereas their mass activities were similar. PdNi/C and PdAg/C also exhibited higher specific activity than Pt/C for potentials lower than ca. 0.4 V versus Ag/AgCl, but their mass activity was lower. The high ORR activity of PdZn/C, which renders it a promising alternative to Pt-based cathodic electrocatalysts in PEMFCs, was associated with the presence of Pd-Zn alloy in the active phase, as revealed via XRD and TEM.