Low-temperature and one-pot synthesis of sulfurized graphene nanosheets via in situ doping and their superior electrocatalytic activity for oxygen reduction reaction

The chemical doping of foreign atoms and functional moieties is a significant strategy for tailoring the electronic properties and enhancing the catalytic ability of graphene. However, the general approaches to the synthesis of heteroatom-doped graphene often involve chemical vapor deposition (CVD) and/or thermal annealing performed at high temperature under gas phases, which require special instruments and tedious process. In this study, we have developed a low temperature, economical, and facile one-pot hydrothermal method to synthesise sulfur-doped reduced graphene oxide (S-RGO) nanosheets, in which the sodium sulfide (Na2S) was employed not only as a sulfur source but also as a reductant to reduce the graphene oxide (GO) simultaneously with sulfur (S) being in situ doped into graphene frameworks. The as-prepared S-RGO has a high S content (4.19 at%), as well as high-quality sulfurated species (mainly as C-S-C-), and possesses numerous open edge sites and defects on its surface, which are beneficial for the improved ORR catalytic activity. Electrochemical characterizations clearly demonstrated the excellent electrical conductivity and superior electrocatalytic activity of S-RGO for oxygen reduction reaction (ORR), coupled with considerably enhanced stability and methanol tolerance compared to the commercial Pt/C catalyst. The present low temperature and one-pot approach provides the possibility for the synthesis of S-RGO at the Gram-scale for its application in electronic nanodevices and electrode materials for fuel cells.