Carbon-supported palladium-cobalt-noble metal (Au, Ag, Pt) nanocatalysts as methanol tolerant oxygen-reduction cathode materials in DMFCs

The carbon-supported nanoparticles of Pd-Co-M (M=Pt, Au, Ag) catalysts for direct methanol fuel cells (DMFCs) in a ratio of (70:20:10) were prepared through reverse microemulsion method. The X-ray diffraction (XRD) analysis showed well-defined reflections corresponding to a face centered cubic phase of palladium. From transmission electron microscopy analysis, the particle size after heat-treatment at 500 degrees C was found to be approximately 20 nm, which was also confirmed by XRD analysis. Polarization data indicated Pd-Co-Pt to have better oxygen reduction reaction (ORR) activity than the other combinations with Ag and Au, in terms of shift in onset potential to a positive value of more than 100 mV and increased reduction current. The ORR kinetics on Pd-Co-Pt was analyzed by using rotating disk electrode to follow a 4 electron pathway, the order of the reaction being unity. The peroxide formation estimated from the rotating ring disk electrode measurements was found to be a negligibly small amount of 1.1%. An additional advantage observed with Pd-Co-Pt was its high methanol tolerance and ORR activity nearly equal to Pt.