Synthesis of functionalized 3D porous graphene using both ionic liquid and SiO₂ spheres as "spacers" for high-performance application in supercapacitors

In this work, a high-capacity supercapacitor material based on functionalized three-dimensional (3D) porous graphene was fabricated by low temperature hydrothermal treatment of graphene oxide (GO) using both ionic liquid (IL) and SiO₂ spheres as "spacers". In the synthesis, the introduction of dual "spacers" effectively enlarged the interspace between graphene sheets and suppressed their re-stacking. In addition, the IL also acted as a structure-directing agent playing a crucial role in inducing the formation of unique 3D architectures. Consequently, fast electron/ion transport channels were successfully constructed and numerous oxygen-containing groups on graphene sheets were effectively reserved, which had unique advantages in decreasing ion diffusion resistance and providing additional pseudocapacitance. As expected, the obtained material exhibited superior specific capacitance and rate capability compared to single "spacer" designed electrodes and simultaneously maintained excellent cycling stability. In particular, there was nearly no loss of its initial capacitance after 3000 cycles. In addition, we further assembled a symmetric two-electrode device using the material, which showed outstanding flexibility and low equivalent series resistance (ESR). More importantly, it was capable of yielding a maximum power density of about 13.3 kW kg^-1 with an energy density of about 7.0 W h kg^-1 at a voltage of 1.0 V in 1 M H₂SO₄ electrolyte. All these impressive results demonstrate that the material obtained by this approach is greatly promising for application in high-performance supercapacitors.