| dc.description.abstract | In this study, we report a flexible supercapacitor including a unique macroporosity self-assembly of graphene as electrode. The graphene supercapacitor made by three-dimensional graphene electrodes were prepared by electrochemical exfoliated graphene (EC-graphene) follow by freeze-dried and annealed process. Here we study the effects of macroporous structured electrodes on capacitor performance by altering the graphene concentration. Moreover, flexible supercapacitor devices made by such unique electrodes were demonstrated by using gel electrolyte (1M H2SO4 /PVA).
We found out the pore size of 3D graphene electrodes correlated to the solution concentration of initial graphene suspension, where the pore size were 4.88μm, 1.19μm, 1.02μm, 0.39μm corresponding to 10 mg/mL, 15 mg/mL, 20 mg/mL, and 25 mg/mL, respectively.
The result shows that graphene electrode exhibit superior high specific capacitance of 45.40 F/g in liquid electrolyte (6M KOH) and 23.89 F/g in gel electrolyte (1M H2SO4/PVA) at low concentration of graphene (10mg/mL), which was higher than that (31.85 F/g in liquid electrolyte and 10.43 F/g in gel electrolyte) of samples prepared at high concentration (25 mg/mL). The device shows excellent rate performance and cycling stability. It was clearly seen the larger pore sized electrodes, result in higher capacitance which was due to few-layered stacked graphene creating more accessible surface area and better kinetic process of ion diffusion.
In addition, it can be seen that the dipping method can be used to gain higher performance of flexible supercapacitor. The specific capacitance of EC-graphene without dip is 17.23 F/g (27.91% lower than dipping method). This can be caused by higher efficient ion diffusion in sample dips into dilute PVA-H2SO4 electrolyte due to more time electrolyte immersed into electrode. Moreover, it was found out that EC-graphene shows higher performance than conventional used reduced graphene oxide(rGO) (43.45 F/g in 6M KOH electrolyte), which was attributed to its poor electrical conductivity (sheet resistance of rGO 7.07x10-3 Ω/sq while EC-Graphene 6.60 x10-3 Ω/sq) and lower oxygen functional groups.
The flexible supercapacitor, exhibit superior working stability during the bending testing, where 94% of capacitance was preserved for bending angle up to 180o and 90% after 50 times bending cycles. This work introduces a new concept of flexible, environment friendly, large scale production, and high performance graphene-based supercapacitors that could have a way for practical applications in energy devices. | en_US |