Oxygen reduction reaction on AgPd nanocatalysts prepared by galvanic exchange

Abstract

In this work galvanic exchange was employed as bimetallic catalyst preparation method to obtain AgPd nanocatalysts. Ag nanoparticles synthesized by the citrate method and commercial silver nanowires (AgNWs) were used for Pd spontaneous deposition. From transmission electron microscopy images, the particle sizes were determined between 10 and 20 nm and AgPd particles with the Ag/Pd molar ratio of 18:82 obtained using MP-AES were larger compared to those of 89:11 ratio. The galvanic exchange process resulted in porous and half-moon shaped particles. Pd distribution for AgPd/C_1 (18:82) and AgPd/C_2 (56:44) catalysts was rather uniform. Decreasing the amount of Pd salt in the galvanic exchange bath led to only surface decoration of Ag particles as can be seen in the case of AgPd/C_3 (79:21) and AgPd/C_4 (89:11). AgPd120NW and AgPd80NW samples showed the Ag/Pd ratio of 82:18 and 94:6, respectively. The electrocatalysts were studied for oxygen reduction reaction (ORR) in alkaline media using the rotating disk electrode technique. Higher specific activity values for ORR were obtained on larger particles, however galvanic exchange process was not limited to surface layers, thus increasing Pd content resulted in lower mass activities. For all the AgPd catalysts a typical Tafel slope value of ∼−60 mV was observed.