Carbon nanotube spaced graphene aerogel has been prepared by a hydrothermal method and used for supercapacitor applications. The specific surface area and specific capacitance can be controlled by tuning the amount of added carbon nanotubes. The as-prepared composite aerogel keeps the advantage of aerogel structure in providing macropores to ensure electrodes fast wetted by the electrolyte ions, and also possesses additional mesopores created by the carbon nanotube spacers for more ion adsorption. Benefited from that, the composite aerogel exhibit significantly enhanced supercapacitor properties in both aqueous and ionic liquid electrolyte. Compared with graphene aerogels, the composite aerogels show a 37 % © 2014. This manuscript version is made available under the Elsevier user license http://www.elsevier.com/open-access/userlicense/1.0/ 2 larger specific capacitance of 245.5 F g -1 at a current density of 2.5 A g -1 , and high rate capability of 197.0 F g -1 at a high current density of 80 A g -1 in aqueous electrolyte. Moreover, the composite aerogels also deliver a 33 % larger specific capacitance of 183.3 F g -1 at 0.5 A g -1 and a high energy density of 80 Wh kg -1 when using an ionic liquid (EMIMBF 4 ) as the electrolyte.
We have successfully assembled graphene nanosheets into spherical shells using polystyrene spheres as templates. Compared with stacked planar graphene, the as-prepared graphene spherical shells have more free space in between the spheres, which results in a larger accessible surface area for adsorption of electrolyte ions in supercapacitors. Electrochemical tests show that the graphene hollow spheres exhibit a high specific capacitance of 273 F g À1 and excellent electrochemical stability.
Ionic liquid modified graphene for supercapacitors with high rate capability, Electrochimica Acta http://dx. Graphical abstractHighlights Ionic liquid is used to functionalize the graphene electrodes of supercapacitor; Treated electrodes become more compatible with the same electrolyte; Rate capability is improved with the treated graphene electrodes. Abstract:Ionic liquids (ILs) with large electrochemical windows up to 4 V have been employed as the electrolyte to boost the energy density of graphene-based supercapacitors.However, due to the larger molecular size, lower conductivity, and higher viscosity of the IL electrolyte, graphene-based supercapacitors in IL electrolyte usually exhibit 2 low rate capability. To make graphene-based electrodes more compatible with the IL electrolyte, we functionalized chemically reduced graphene oxide with the same IL which is also used as the electrolyte. Electrochemical test results show that the relaxation time and charge transfer resistance at electrode-electrolyte interface for IL modified electrode is one third and one fourth of that for the pristine graphene electrode, respectively, indicating the improved compatibility between the IL modified electrode and the electrolyte. Furthermore, the capacitance retention of the IL modified electrode from current density of 0.5 to 20 A g -1 is 85 %, which is much higher than that of the pristine electrode (53%).
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