Graphene-Manganite-Pd Hybrids as Highly Active and Stable Electrocatalysts for Methanol Oxidation and Oxygen Reduction

Hybrids of graphene nanosheets (GNSs) with Pd and MMn2O4 (M = Mn & Co) have been prepared and investigated as electrocatalysts for the methanol oxidation (MOR) and oxygen reduction (ORR) reactions in 1 M KOH at 25 °C. Results show that incorporation of Mn3O4 (or CoMn2O4) into 40wt%Pd/GNS increases the electrocatalytic activity toward both the reactions (MOR and ORR) greatly; the observed enhancement in the activity being much higher with CoMn2O4 addition. It is observed that at an anodic potential, E = 0.610 V vs RHE, 8wt% CoMn2O4 addition improves the methanol oxidation current density of 40wt%Pd/GNS by more than 3 times. Similarly, at E = 0.90 V vs RHE, 5wt% CoMn2O4 addition improves the ORR activity of 40wt%Pd/GNS nearly two times. The stability of the active hybrid electrode is also found to be outstanding under both MOR and ORR conditions. Similar stabilities have not been found with other fuel cell catalysts. In a chronoamperometry experiment at E = 0.626 V vs RHE, the methanol oxidation current observed on Pd-8%CoMn2O4/GNS at 2 min decreased by only ∼5% at 120 min.