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.