Graphene aerogel derived by purification-free graphite oxide for high performance supercapacitor electrodes

Abstract

Graphite oxide (GO), often being used as a precursor of graphene-based materials, can be prepared through a modified Hummers' method. The last step of GO synthesis, i.e. the removal of hydrogen chloride (HCl), is generally time-consuming, costly and polluting. Herein, the HCl-containing graphite oxide (H-GO) and pure GO aqueous suspensions were respectively hydrothermally treated followed by freeze-drying, leading to two graphene aerogels (H-GA and GA). Characterization results show that the two aerogels possess similar microstructure but distinct surface chemistry properties. When used as the active electrode materials in supercapacitors, GA and H-GA show comparable electrochemical properties in KOH aqueous electrolyte. In EMIMBF4 ionic liquid electrolyte, H-GA shows larger specific capacitance (243 F g−1 at 1 A g−1), better rate capability, and higher energy density (135 Wh kg−1 at 1 kW kg−1) compared with GA (216 F g−1, 120 Wh kg−1), which is attributed to its higher O/C ratio and better electrolyte wettability. We propose that it is not always necessary to conduct the HCl removal, and H-GO could be directly used as a precursor, which not only saves the time and cost remarkably but also may open up a relatively facile route to fabricate some graphene-based functional bulk materials.