Hierarchically Porous Graphene Aerogels with Abundant Oxygenated Groups for High-Energy-Density Surpercapacitors

Abstract

A hierarchically porous graphene aerogel (HP-GA) with abundant oxygenated groups and hand-tearing bread-like macromorphology is achieved by a sacrificial MnO 2 template approach. Oxygenated groups on graphene sheets improve the wettability of HP-GA to an aqueous electrolyte and contribute to pseudocapacitance. The chlorine (Cl 2 ) gas as a result of the reaction of MnO 2 and HCl is responsible for the formation of the hierarchically porous microstructure and hand-tearing bread-like macromorphology, ensuring a large electrolyte accessible surface area within the electrodes. When used as the active electrode material in supercapacitors, HP-GA exhibits a large specific capacitance of 284 F g −1 at 1 A g −1 and ultrahigh energy density of 10 Wh kg −1 at 250 W kg −1 in an aqueous electrolyte. This work provides a versitile, simple, and easy to control way to alter the microstructure and macromorphology of graphene-based areogels that have promising applications in many areas, including adsorption, energy storage, heat insulation, acoustical insulation, and intelligent sensing system.

One-Step Synthesis of Fragment-Reduced Graphene Oxide as an Electrode Material for Supercapacitors

“…GCD curves at 1–20 A/g (a), CV curves at 10–200 mV/s (b), and (c) Ragone plots of FrGO (1:4, 180 °C, 3 h), reported carbon materials, ,− and commercial SCs (Table S8). …”

“…At the same time, as the charge and discharge progress, more OCFGs on the surface of the graphene material inside the electrode material are activated or introduced. These are the main reasons for the increase in capacitance retention of electrode materials. ,,,,, …”

“…Xu et al reported the self-assembled graphene hydrogel prepared by the hydrothermal method, and the specific capacitance is 175 F/g at a scan rate of 10 mV/s . However, the rGO obtained via the hydrothermal method mostly has a gravimetric specific capacitance below 300 F/g. − …”

“…Steric effects will limit the ion access when the micropores are smaller than the solvation shell ions (ion sieve effect), and this part of the micropore cannot store energy. Therefore, many researchers have studied that the macroporous structure in materials can serve as a buffer zone to store electrolyte ions, thereby minimizing the diffusion distance of ions, and the mesoporous structure can provide a larger accessible surface area for ion attraction in EDLCs and promote electrodes’ capacitance retention. ,,− In the preparation of graphene material, affected by the influence of interlayer π–π electrons and van der Waals forces, it is easy to cause interlayer aggregation/restacking of graphene material during the reduction process, which will limit the access of electrolyte ions into the graphene layer and limit the number of active sites, resulting in low ratio capacitance and low conductivity . Some studies have prepared graphene composites or porous materials using various ″spacer″ materials, such as carbon, metal oxides, and polymers.…”

Applications of Graphene in Five Senses, Nervous System, and Artificial Muscles

“…Graphene can be divided into several types according to their morphologies and dimensions, such as 0D quantum dots, − 1D nanoribbons, − nanosheets, − flakes, , 2D films, − and 3D macroforms. − The 0D quantum dots can be used in fluorescence imaging and light emission devices. The 1D nanoribbon provides a platform for topological insulators , and Dirac physics .…”