Sulfur modification of worm-like exfoliated graphite with crumpled graphene sheets derived from mesocarbon microbeads for electrochemical supercapacitors

Chemical exfoliation and unzipping of graphitic mesocarbon microbeads tend to form bone-like aggregates of graphene oxide (GO) sheets (marked as O-EMCMB). Heat treatment of O-EMCMB leads to the formation of partially reduced GO fragments (marked as HT-EMCMB) with hydrophobic sheets. Sulfur doping of O-EMCMB through hydrothermal process with sodium sulfide results in the formation of sulfur-doped and reduced GO with worm-like shape (marked as S-EMCMB). S-EMCMB has more crumpled sheets and hydrophilic surface than HTEMCMB. Cyclic voltammetry reveals that S-EMCMB electrode gains more pseudocapacitive charge-storage capacity than the O-EMCMB and HT-EMCMB electrodes in 6 M KOH solution. S-EMCMB electrode exhibits high rate performance, cycling stability, and coulombic efficiency during galvanostatic charge and discharge (GCD) processes, its specific capacitance attains 314 F g(-1), far greater than the O-EMCMB (67 F g(-1)) and HT-EMCMB (222 F g(-1)) under a GCD current of 1 A g(-1). The enhanced charge-storage properties of S-EMCMB can be ascribed to its high hydrophilicity and electrical conductivity after incorporation of sulfur-related functional groups into the crumpled graphene sheets. This unique worm-like configuration inhibits graphene sheets from restacking and enables rapid transport of ions and electrons through hydrophilic pores for facilitating the redox kinetics at the electrolyte-electrode interfaces.

Automated summary

Chemical exfoliation and unzipping of graphitic mesocarbon microbeads can lead to the formation of bone-like aggregates of graphene oxide. Different treatments can result in partially reduced GO fragments with hydrophobic sheets or sulfur-doped and reduced GO with a worm-like shape. The sulfur-doped GO exhibits enhanced charge-storage properties due to its high hydrophilicity, electrical conductivity, and unique worm-like configuration. It has higher pseudocapacitive charge-storage capacity and better rate performance compared to the other two types of electrodes.