Aqueous, Mixed Micelles as a Means of Delivering the Hydrophobic Ionic Liquid EMIM TFSI to Graphene Oxide Surfaces

Ultrafast and Reversible Superwettability Switching of 3D Graphene Foams via Solvent-Exclusive Plasma Treatments

For highly active electron transfer and ion diffusion, controlling the surface wettability of electrically and thermally conductive 3D graphene foams (3D GFs) is required. Here, we present ultrasimple and rapid superwettability switching of 3D GFs in a reversible and reproducible manner, mediated by solvent-exclusive microwave arcs. As the 3D GFs are prepared with vapors of nonpolar acetone or polar water exclusively, short microwave radiation (≤10 s) leads to plasma hotspot-mediated production of methyl and hydroxyl radicals, respectively. Upon immediate radical chemisorption, the 3D surfaces become either superhydrophobic (water contact angle = ∼170°) or superhydrophilic (∼0°), and interestingly, the wettability transition can be repeated many times due to the facile exchange between previously chemisorbed and newly introduced radicals via the formation of methanol-like intermediates. When 3D GFs of different surficial polarities are incorporated into electric double-layer capacitors with nonpolar ionic liquids or polar aqueous electrolytes, the polarity matching between graphene surfaces and electrolytes results in ≥548.0 times higher capacitance compared to its mismatching at ≥0.5 A g-1, demonstrating the significance of wettability-controlled 3D GFs.

Reduced graphene oxide/ionic liquid composites with tunable interlayer spacing for improved charge/discharge kinetics in supercapacitors

The large specific surface area and high conductivity of reduced graphene oxide (RGO) make it a promising material for supercapacitors. However, aggregation of graphene sheets into graphitic domains upon drying hampers supercapacitor performance by drastically impeding ion transport inside electrodes. Here, we present a facile approach to optimize charge storage performance in RGO-based supercapacitors by systematically tuning their micropore structure. To this end, we combine RGOs with room temperature ionic liquids during electrode processing to impede stacking of sheets into graphitic structures with small interlayer distance. In this process, RGO sheets function as the active electrode material while ionic liquid serves both as a charge carrier and a spacer to control interlayer spacing inside electrodes and form ion transport channels. We show that composite RGO/ionic liquid electrodes with larger interlayer spacing and more ordered structure exhibit improved capacitance and charging kinetics.