Carbon Supported Noble Metal (Pd and Au) Catalysts Synthesized by an Oxide Route with High Performance for Oxygen Reduction in Acidic Media

Abstract

Carbon supported palladium (C/Pd) and gold (C/Au) catalysts were synthesized through a synthesis route involving oxide precipitation and partial reduction, and their performance for the oxygen reduction reaction (ORR) in acidic media was studied. Scanning electrochemical microscopy (SECM) ORR screening and tip-generation/substrate collection performed on glassy carbon supported metal spots showed a strong effect of the reactant ratio (precursor salt/precipitant/reducing agent) on the performance of the resulting catalysts for oxygen reduction and hydrogen peroxide production. These SECM results were further confirmed using a rotating ring-disk electrode with Nafion-embedded Vulcan carbon supported dispersed metal nanoparticles, and characterization with XRD and TGA. A significant enhancement in the overall activity for the ORR was observed on both C/Pd and C/Au catalysts under conditions involving metal oxide reduction, compared to those catalysts that were synthesized by direct metal salt reduction. For C/Pd, this enhanced overall activity with concomitant low peroxide yield is due to the different ways in which the metal and unreduced metal oxide in the catalysts interact with the hydrogen peroxide pathway. For C/Au, a highly dispersed metal with high electroactive area is obtained that shifts the potentials for the reduction of oxygen to hydrogen peroxide to near-reversible conditions.