Tailoring the oxygenated groups of graphene hydrogels for high-performance supercapacitors with large areal mass loadings

High-performance electrodes with high areal capacitances are highly desired for the practical applications of supercapacitors. Herein, we report such electrodes prepared from hydroxyl-rich graphene hydrogels (HRGHs). The hydroxyl groups on graphene sheets contribute to pseudo-capacitance and improve the wettability of HRGHs to aqueous electrolyte, ensuring fast ion transport within the electrodes, especially for the electrodes with high mass loadings. The supercapacitor based on mechanically compressed HRGHs shows a high gravimetric capacitance (260 F g(-1)) and volumetric capacitance (312 F cm(-3)) at 1 A g(-1), good rate capability (similar to 78% at 100 A g(-1)), and excellent cycling stability (similar to 100% after 10 000 cycles). Moreover, an ultrahigh areal capacitance of 2675 mF cm(-2) at 1 mA cm(-2) is achieved at the mass loading of 10 mg cm(-2). Even at a high current density of 50 or 100 mA cm(-2), the areal capacitance is still retained at 2140 or 1768 mF cm(-2), demonstrating the outstanding scalability of the HRGH electrodes.