Pd-Zn/C bimetallic electrocatalysts for oxygen reduction reaction

A series of eight 10 wt% Pd-Zn/C electrocatalysts were synthesized via wet impregnation and compared concerning their activity for the oxygen reduction reaction (ORR) in 0.1 M HClO4 and room temperature, using the thin-film rotating disk electrode technique. The electrocatalysts differed in Pd:Zn mass ratio and reduction temperature. Pt/C, Pd/C and Zn/C electrocatalysts of 10 wt% metal loading, also prepared via wet impregnation and reduced at 300 A degrees C, were used as reference. The highest activity among the Pd-Zn/C, Pd/C and Zn/C electrocatalyts was exhibited by Pd-Zn/C reduced at 300 A degrees C and with a Pd:Zn mass ratio equal to 3:1. Its specific activity was higher than that of 10 wt% Pt/C (by ca. 3.5 times at 0.5 V vs. Ag/AgCl), whereas their mass activities were similar. On the contrary, the ORR specific activity of a 29 wt% Pd-Zn/C electrocatalyst reduced at 300 A degrees C and with Pd:Zn mass ratio 3:1 was lower than that of a 29 wt% Pt/C electrocatalyst prepared in the same manner, by ca. 3.7 times at 0.5 V vs. Ag/AgCl, although their mass activities were similar above this potential. Both these catalysts were clearly less active than a commercial (TKK) 29 wt% Pt/C electrocatalyst. [GRAPHICS] .