(709b) Novel Hybrid Electrode-Electrolyte Materials Based on Ionic Liquids and Reduced Graphene Oxide for Supercapacitors

Supercapacitors are energy storage devices that store energy physically by excess ion accumulation near the electrode surface. A large electrochemical surface area is essential in improving the capacitance. Therefore, carbonaceous materials with large surface area are widely used. However, the large portion of the physically available electrode surface area originates from micropores that are inaccessible to hydrated or solvated ions. Additionally, during supercapacitor assembly, it is a challenge to ensure complete wetting of the pores while eliminating trapped gases. We addressed these challenges by designing a hybrid electrode-electrolyte material where an ionic liquid (IL) is encapsulated within reduced graphene oxide (rGO) shell. The utility of the hybrid material (rGO-IL) is three folds: (1) increased potential range by ILs, in comparison to aqueous and organic solvent based electrolytes; (2) almost complete wetting of the electrode achieved inherently without a post electrolyte impregnation step; (3) ready-to-use active material in contact with the electrolyte. We demonstrate the proof of concept by synthesis through Pickering-type emulsions consisting of a dispersed phase of 1-methyl-3-butylimidazolium hexafluorophosphate, [bmim][PF₆], and a continuous water phase where GO sheets were used as the surfactant. Interfacial polymerization during the synthesis yielded polyurea which bound the nanosheets together to form the capsule shell. The performance of the rGO-IL hybrid as a supercapacitor material was evaluated based on measured capacitance of the fabricated symmetrical coin cells by cyclic voltammetry (CV) as a function of scanning rate (500 – 10 mV/s) at 18 and 60 ËšC. The specific capacitance of rGO-IL was 80 and 26 F/g at 10 and 500 mV/s, respectively at 18 ËšC; compares favorably with respect to just the rGO shell material or the common porous carbon (YP-50) with the same IL as the electrolyte. At 60 ËšC, the specific capacitance increased by 1.6-fold (126.77 F/g at 10 mV/s) for the rGO-IL, while it increased by 2-fold (89.95 F/g at 10 mV/s) with rGO electrode. The smaller change of the capacitance indicated that the inaccessible surface area within rGO-IL hybrid electrode was smaller than rGO electrode. The characterization of rGO-IL hybrid material by SEM, TGA and Raman will be presented as well as the electrochemical measurements of impedance and cycling stability.