Platinum nanoparticles encapsulated in nitrogen-doped graphene quantum dots: Enhanced electrocatalytic reduction of oxygen by nitrogen dopants

Nitrogen-doped graphene quantum dots (NGQDs) prepared by hydrothermal treatment of citric acid and urea were used as an effective support for platinum nanoparticles synthesized by carbon monoxide reduction of Pt(IV) in water. TEM measurements showed that the platinum nanoparticles were 2.03 ± 0.43 nm in diameter, and wrapped with one layer of NGQDs, as compared to results from AFM measurements. XPS measurements confirmed the formation of metallic platinum and the incorporation of nitrogen dopants within the graphitic molecular skeleton, and the shifts of Pt 4f binding energy suggested that charge transfer from Pt to NGQDs was facilitated by the more electronegative nitrogen dopants, as compared to platinum nanoparticle supported on undoped GQDs (Pt-GQDs). Because of this, the Pt-NGQDs nanocomposites showed markedly enhanced catalytic activity towards oxygen reduction reactions in alkaline media, as compared to Pt-GQDs, with a specific activity more than three times that of commercial Pt/C. Further comparison with NGQDs-supported gold nanoparticles showed that the platinum nanoparticles, rather than the NGQDs, played a dominant role in determining the ORR activity.