Oxygen Reduction Catalyzed by Platinum Nanoparticles\nSupported on Graphene Quantum Dots

Abstract

Nanosized\ngraphene quantum dots were prepared by acid etching of carbon fibers\nand used as effective substrate supports for platinum nanoparticles\nwhich were synthesized by thermolytic reduction of platinum­(II) chloride\nin ethylene glycol. Transmission electron microscopic measurements\nshowed that the resulting nanocomposite (Pt/G) particles exhibited\nan average diameter of 2.79 ± 0.38 nm, with clearly defined lattice\nfringes of 0.23 nm that might be assigned to the interlayer spacing\nof the (111) crystal planes of <i>fcc</i> Pt. In addition,\nthe Pt nanoparticles were found to be wrapped with a low-contrast\nhalo that likely arose from the poorly crystalline graphene quantum\ndots. X-ray diffraction studies confirmed the composite nature of\nthe Pt/G nanoparticles, and the average size of the crystal domains\nof the Pt/G nanoparticles was found to be close to the nanoparticle\nphysical dimensions, whereas for commercial Pt/C nanoparticles the\nsize of the crystal domains was only half that of the nanoparticle\ndiameter. XPS measurements showed the formation of metallic platinum\nalong with sp² and oxygenated carbons in the nanocomposite\nnanoparticles. Significantly, in comparison with commercial Pt/C catalysts,\nthe Pt/G nanocomposites showed markedly enhanced catalytic activity\nin oxygen reduction reactions, with an onset potential of +1.05 V\nthat was 70 mV more positive than that of Pt/C, and a specific activity\nthat was almost nine times higher. These results were ascribed to\nthe abundant structural defects of the nanosized graphene quantum\ndots that manipulated the dissociative adsorption of oxygen and the\nbinding of reaction intermediates O* and HO* on platinum surfaces.