Construction of three-dimensional porous graphene with N,S co-doping in KOH-K2CO3 eutectic active molten salt system for supercapacitors

Abstract

We prepared a three-dimensional porous graphene (3DPG) with N or/and S doping (N-3DPG, S-3DPG, NS-3DPG) in the KOH-K2CO3 eutectic active molten salt system. Graphene oxide, urea, and 3-mercaptopropionic acid are adopted as the 3DPG, nitrogen, and sulfur precursors, respectively. As a result, a continuous 3D network with dense cross-linked architecture is gained because the KOH-K2CO3 medium works as template to accelerate the conversion of GO to 3D architecture. A specific capacitance of 521 F/g is obtained for the NS-3DPG, which is much larger than that of 3DPG, N-3DPG, S-3DPG. A symmetric supercapacitor NS-3DPG||NS-3DPG delivers an energy density of 21.7 Wh/kg at a power density of 300 W/kg, and displays the capacitance retention ratio of 98.0 % after 10,000 cycles. An asymmetric supercapacitor 3DPG||NS-3DPG is assembled, which shows an energy density as high as 33.6 Wh/kg at a power density of 400 W/kg and little capacitance fading for 10,000 cycles. Outstanding supercapacitor performances of the 3DPG||NS-3DPG are attributed to its excellent 3D hierarchical porous structure and the synergistic effect of N,S co-doping.