Title : Preparation and electrochemical capacitive properties of graphene-siloxene hydrogels
Supercapacitor has attracted a great deal of interest because of its higher power density and longer cycling life compared with those of other electrochemical energy storage devices. In the past decades, graphene, as one of the most promising candidates, has been received great attention because of its large theoretical specific surface area (about 2600 m2 g-1), high electronic conductivity and excellent chemical stability. The electrochemical properties of graphene-based supercapacitor electrode materials are closely related to their architecture and chemical nature. Herein, we developed 3D oxygen-rich graphene-siloxene hydrogels (O-GSH) via an one-step hydrothermal method using graphene oxide (GO) and siloxene as precursors. In O-GSH, siloxene as a 2D inserting material forms an extensive π-conjugated structure with graphene, which induces high structural stability and large specific surface area, thus significantly improving the capacitive performance. More importantly, it can also serve as a protective agent to anchor the oxygen atoms on the reduced GO (rGO) sheets during the hydrothermal process, leading to oxygen-rich graphene-siloxene hydrogels. Via the dehydration reaction between GO and siloxene, new oxygen-containing functional group (C-O-Si) generates to contribute to the pseudo-capacitance. Meanwhile, the introduced oxygen-containing polar bonds can greatly increase the wettability of O-GSH, which is useful for the charge storage behavior in aqueous electrolytes and the acceleration of transfer rate of electrolyte ions. Thus, the developed O-GSH (graphene/siloxene = 3:1) exhibits a high specific capacitance of 520 F g-1 at 1 A g-1 in a three-electrode system in 1 M H2SO4 aqueous solution. Moreover, O-GSH (3:1) has an excellent stability (approximately 96.3% retention of the initial specific capacitance after 15000 cycles at a high current current of 50 A g-1). Furthermore, the assembled symmetrical supercapacitor of O-GSH (3:1)//O-GSH (3:1) has a high energy density of 24.5 Wh kg-1 at the power density of 399.6 W kg-1. These imply that O-GSH (3:1) may be a promising electrode material in high-performance supercapacitors.