Facile preparation of nitrogen/sulfur co-doped and hierarchical porous graphene hydrogel for high-performance electrochemical capacitor

Nitrogen/sulfur co-doped and hierarchical porous graphene hydrogels (DHGHs) are prepared by facile self-assembly process. The results show that the pH values of preparation process significantly affect the microstructures and electrochemical properties of DHGHs and the mechanism has been discussed. The as-prepared DHGHs can be directly used as binder-free electrodes to assemble full-cell supercapacitor devices. It is surprising that the DHGHs prepared at basic condition (DHGH-12) delivers a specific capacitance of 251 F g(-1) (0.5 A g(-1)). Moreover, the DHGH-12 shows rectangular cyclic voltammetry shape at a high scan rate of 3000 mV s(-1) and symmetrical galvanostatic charge/discharge curves at 100 A g(-1) which exhibits a specific capacitance of 136.5 F g(-1), a high energy density of 4.74 Wh kg(-1) and high power density of 25.47 kW kg(-I). Additionally, DHGH-12 presents superior cycling stability (96.8% retention after 2000 cycles at 20 A g(-1)) in 6 M ICOH solution. Therefore, the novel DHGHs can be considered as promising candidate for high energy density supercapacitors at high rates. (C) 2017 Elsevier B.V. All rights reserved.