In situ synthesis of sulfur-doped graphene quantum dots decorated carbon nanoparticles hybrid as metal-free electrocatalyst for oxygen reduction reaction

In this study, we have successfully prepared in-situ synthesis of sulfur-doped graphene quantum dots decorated carbon nanoparticles (S-GQDs/CNPs) hybrid from low-cost fructose and H2SO4 by the hydrothermal method. Fructose molecules are dehydrated by concentrated sulfuric acid, then formed honeycomb carbon matrix including sulfate radical in the hydrothermal process, while H2SO4 catalyses the reaction and offers sulfur atom for the carbon material. The result of transmission electron microscopy (TEM) demonstrates that a lot of in-situ grown S-GQDs are decorated on carbon nanoparticles by π–π stacking in the hydrothermal process, advantages of both GQDs and carbon nanoparticles combined, which facilitates the electron transfer between S-GQDs and carbon nanoparticles. X-ray photoelectron spectroscopy (XPS) and Fourier Transform Infrared (FT-IR) spectra show the presence of –C–S–C– bonds and the absence of oxygen-containing groups in S-GQDs/CNPs hybrid. As expected, the electrochemical data of S-GQDs/CNPs hybrid indicate that the layer by layer modified method can inhibit the occurrence of a two-electron pathway and cause a four-electron pathway for ORR. Moreover, the resulting S-GQDs/CNPs hybrid has a better methanol tolerance and long-term durability than commercial 20% Pt/C.