Preparation Of 3D Porous FeC₂O₄/graphene And MnO₂/graphene Electrode Materials And Application In Suercapacitors

Supercapacitor,also known as electric double layer capacitor,is a new type of energy storage device between a battery and an ordinary capacitor.It has the characteristics of high charge and discharge speed,good cycle stability,environment friendly and high efficiency,etc.Electrode material is the key material impact supercapacitor performance.Therefore it is very important for us to prepare high-performance electrode material.Graphene has a high specific surface area and good electrical conductivity.It can be used as an electrode material and has good cycle stability and can store more charges.The disadvantage is that the specific capacitance is limited.When the metal oxide is used as an electrode material,the specific capacitance is large but the electrical conductivity and the cycle stability are poor.Therefore,a new material is prepared by loading a metal oxide onto graphene,and it is used as an electrode material.In this dissertation,FeC2O4/rGO and MnO2/rGO composites were investigated.The preparation and properties of high performance supercapacitor electrode materials were studied.Distinguished from commonly used Fe2O3 and Fe3O4,a three-dimensional multilevel macro-micro-mesoporous structure of FeC2O4/graphene composite has been prepared as binder-free electrode for supercapacitors.The as-prepared materials are composed of macroporous graphene and microporous/mesoporous ferrous oxalate.Generally,the decomposition voltage of water is 1.23V and the practical voltage window limit is about 2V for asymmetric supercapacitors in aqueous electrolytes.When FeC2O4/rGO hydrogel was used as the negative electrode and a pure rGO hydrogel was used as the positive electrode,the asymmetrical supercapacitor voltage window raised to 1.7V in KOH(1.0M)electrolyte and reached up to 2.5V in a neutral aqueous Na2SO4(1.0 M)electrolyte.Correspondingly it also exhibits a high performance with an energy density of 59.7 Wh kg-1.Similarly,a three-dimensional porous MnO2/rGO composite was also prepared,consisting of macroporous graphene and mesoporous MnO2.When FeC2O4/rGO hydrogel was used as the negative electrode and a MnO2/rGO hydrogel was used as the positive electrode,the asymmetrical supercapacitor voltage reached up to 2.5V in a neutral aqueous Na2SO4(1.0M).By means of combining a metal oxide that owns micro-mesoporous structure with grapphene,this work provides a new opportunity for preparing high-voltage aqueous asymmetric supercapacitors without addition of conductive agent and binder.