Construction And Performance Of An Integrated Supercapacitor Based On Graphene-based Membrane

Supercapacitor?SC?as one of the most important energy storage devices attracts great attention because it can not only realize the fast energy storage and release but also has ultralong cycle life.As a result,the flexible supercapacitor shows great potential as the power source in the flexible electronics that fast develop in these years.Although the assemble technique for the flexible SC has been widely reported,the problems,such as the complicated assembly process,high cost and the weak contact between the electrode and separator,still exist.In this thesis,with the fully considering the electrode materials and device configuration for flexible SC,we proposed a new integrated SC in one graphene membrane and showed a simple fabrication method for it.The main content and conclusion are as follows:For the active material to assemble this SC,we first prepared the uniform dispersion of graphene oxide?GO?and TiO₂ nanoparticles?NPs?by sonication,and then the dispersion was filtrated on the filter to form a thin GO-TiO₂ membrane.With the assistance of the TiO₂,the GO was reduced into reduced graphene oxide?rGO?by UV irradiation induced reduction,and finally,a high performance rGO-TiO₂ membrane electrode was obtained.At the same time,the TiO₂ NPs avoided the aggregation of graphene.We investigated the influences of UV irradiation time on the reduction degree and electrochemical behaviors,and the results show the short irradiation time cannot realize the full reduction of GO which leads to the low conductivity while the prolonged irradiation time removes too much functional groups leading to the loss of the pseudocapacitance.It is found the membrane with a 40 min reduction shows the best electrochemical performance.For the device configuration,we prepared a membrane with the sandwich structure of GO-TiO₂/GO/GO-TiO₂ using a continuous filtration process.After a UV-assisted reduction process,both sides of above membrane were reduced into rGO-TiO₂ forming a rGO-TiO₂/GO/rGO-TiO₂ membrane which can be used as the flexible SC directly.The rGO-TiO₂ layer is used as the active material and the GO layer acts as the separator.We investigated the influences of thickness of GO layer and electrolyte on the electrochemical performance in detail.The results show that the membrane shows the best performance of high volumetric capacitance and volumetric energy density of 237 F cm^-3 and 16 mWh cm^-3 using Na₂SO₄ as the electrolyte and being with the GO layer thickness of 0.78?m.Such configuration and assembly method avoids the destroying of the membrane structure compared to the conventional reduction methods,and thus,ensures the tight contact between these three layers and finally the good flexibility and cyclic stability.Moreover,we also investigated the effects of the morphology of TiO₂ on the electrochemical performance.It is shown the nanoparticles can help realize the more uniform reduction of GO and thus the better electrochemical performance compared with the TiO₂ nanowires.