Effective microwave-hydrothermal reduction of graphene oxide for efficient energy storage

Reduced graphene oxide (rGO) is an important member of the family of graphene-based nanomaterials. Conventional strategies for preparing rGO include chemical, thermal, photo, laser, hydrothermal, and microwave reduction. Here we report on a rapid microwave-hydrothermal (MH) method for the effective production of pure rGO (denoted as M-rGO) without using any reducing agents. The MH process was optimized in terms of temperature and duration to tune the structure and composition of the formed M-rGO to attain high specific capacitance for energy storage. The M-rGO possessed a three-dimensional (3D) interconnected porous structure with the C/O ratio of 9:5. The 3D interconnected structure of M-rGO not only increased the active surface area and enhanced the electrical double layer capacitance, but also improved its stability. Retaining the appropriate proportion of active functional groups also made a notable contribution of pseudocapacitance. The synthesized M-rGO exhibited a much higher capacitance of 298 F g(-1) (1 A g(-1), 0.5 M H2SO4) for a three-electrode system and 263 F g(-1) (0.5 A g(-1), 20% H2SO4-PVA gel) for a two-electrode system, as well as much better capacitance retention and cyclability, in contrast to conventional chemically reduced graphene oxide (C-rGO) and thermally reduced graphene oxide (T-rGO). Moreover, the energy density of the M-rGO was very high (36.6 Wh kg(-1)) at a power density of 0.5 kW kg(-1). This first-rate energy storage performance of the M-rGO can be attributed to its highly active surface area, appropriate carbon-oxygen ratio, porous structure, and interconnected 3D morphology.

Automated summary

This study presents a rapid microwave-hydrothermal (MH) method for the efficient production of pure rGO with a three-dimensional interconnected porous structure. The optimized MH process allows for high specific capacitance and excellent capacitance retention and cyclability. The M-rGO demonstrates superior energy storage performance due to its highly active surface area, appropriate carbon-oxygen ratio, porous structure, and interconnected three-dimensional morphology.