Improved Pd electro-catalysis for oxygen reduction reaction in direct methanol fuel cell by reduced graphene oxide

Noble metallic nano-catalysts supported on carbon based substrates are extensively used as electrodes for direct methanol fuel cells (DMFCs). Pd is a promising alternative to the more expensive Pt whether its catalytic properties should be improved. To this aim, reduced graphene oxide (rGO) was employed in this study as an alternative to conventional carbon black (C) substrates to improve the catalytic properties of Pd. Pd nanobars and Pt nanoparticles were synthesized, by the polyol method, and deposited for comparison both on commercial carbon and rGO. The oxygen reduction reactions (ORRs) at the fabricated electrodes were tested by the Rotating Disk Electrode (RDE) technique in acidic media. To correlate the activity to other physico-chemical properties, the nano-catalysts were characterized by Thermo Gravimetric Analysis (TGA), X-Ray Diffraction (XRD), and Transmission Electron Microscopy (TEM). The electro-catalytic activity of the electrode is importantly affected by the support chosen. Specifically, the Pd nano-catalyst proved an enhanced performance when on rGO, while the Pt counterpart was found being more active when placed on C. This result can be explained with a strong dependence of the ORR on the interaction between the metal nano-catalyst and the carbon based support.