Oxygen reduction catalyzed by nanocomposites based on graphene quantum dots-supported copper nanoparticles

Nanocomposites based on graphene quantum dots (GQDs)-supported copper nanoparticles were prepared by thermal refluxing of copper salts in 1,2-propanediol at 140 C in the presence of GQDs. Transmission electron microscopic measurements showed that the resulting Cu/GQD nanoparticles increased from 5 to 15 nm in average diameter with increasing metal loadings. Raman spectroscopic measurements showed that all nanocomposites exhibited well-defined D and G vibrational bands. X-ray photoelectron spectroscopic studies indicated the formation of Cu2O and CuO in the nanocomposite particles, along with various defect concentrations within the GQD graphitic skeletons. Electrochemical studies showed that the nanocomposites exhibited apparent electrocatalytic activity in oxygen reduction in alkaline media, and the sample with a Cu/C atomic ratio of 2.88% exhibited the best ORR activity among the series, within the context of onset potential, number of electron transfer and kinetic current density. The performance was further improved by deliberate hydrothermal treatments of the sample, and 160 C was identified as the optimal temperature, which was ascribed to manipulation of the electronic interactions between copper nanoparticles and oxygen intermediates by the GQD