Synthesis Of Flexible3D Graphene Architecture Based On Graphene Oxide Nanosheets And Its Application In Electrochemical Capacitor

Electrochemical capacitor (EC), also known as supercapacitor, are emerging as a new class of energy storage device since they can offer a number of outstanding characteristics such as high power density and charging speed, superior cycle lifetime, and relatively maintenance free. However, it is still a great challenge to enhance the energy density of EC. As the main reason of lower energy density is lower specific surface area and disconnected pore of traditional electrode materials, the paper will change and improve these shortcoming by freeze-drying and chemical vapor deposition (CVD) separately. The main content were summarized as following:1. Graphene and3D graphene architecture were synthesis using vacuum filtrating and freeze-drying graphene oxide (GO), separately. Further electrochemical test showed that3D graphene possess higher specific capacitance and charge speed (150F/g at2mV/s and90F/g at200mV/s) than graphene paper (108F/g at2mV/s and65F/g at200mV/s). This is main attributed to higher specific surface area and optimized pore distribution of3D structure. Furthermore, graphene/CNT composite paper also prepared by vacuum filtrating GO and CNT dispersion. The electrochemical performance of the composited paper were investigated at different graphene and CNT ratio.2. The flexible3D frameworks composed of winged G-NFs have been prepared by freeze-drying method assisted by MW irradiation and salt addition, followed with a scalable highly efficient chemical reduction. Furthermore, we propose an electrostatic force induced crimping mechanism for the assembly of G-NFs, where the MW irradiation can play a critical guiding role in the formation of the winged GO-NFs with edge crimped firstly, and the ionic strength of GO solution enhanced by salt addition will further wrinkling GO sheets into nanofibers. Benefited from the highly porous structure and good conductive skeletons of G-NF networks, the MnO2loaded on G-NF frameworks exhibits a remarkably enhanced capacitance than that of G-NS ones. EC measurements indicate that the specific capacitance of MnO2on MnO2/G-NF-based electrodes is enhanced by43%compare to that of G-NS-based ones. Moreover, the total specific capacitance of MnO2/G-NF electrodes is almost double that of the MnO2/G-NS ones. This new kind of3D structure composed of G-NFs show enhanced properties, which will make them have potential applications in the fields of high-performance catalysts, sensors, and energy storage systems.3. A type of freestanding three-dimensional (3D) interconnected structure, with a conjunction of microsized graphene paper, nanosized3D carbon nanotube (CNT) forests, and consequently loaded MnO2nanorods, has been designed as the electrodes of an ultralight flexible supercapacitor. The resulting graphene/CNFs/MnO2composite networks exhibit remarkable flexibility and highly mechanical properties due to good and intimate contacts among them, without current collectors and binders. The high specific capacitance of360F/g from galvanostatic charging/discharging (GCD) were obtained. Furthermore, we have also investigated the superior electrochemical performances of an asymmetric supercapacitor device (weight of less than4mg/cm2and thickness of～30μm), showing a maximum energy density of10Wh/kg. These performances would make our designed supercapacitors become promising candidates for the future flexible and lightweight energy storage systems.