Sodium-ion Capacitor Based On Boron- Doped Graphene/BDD Electrode

Supercapacitor,also known as electrochemical capacitor,is a new type of energy storage device developed in recent years.It has the advantages of high power density,long service life,and environmental protection,etc.So it is widely used in automotive electronics,communications equipment,defense military and other fields.Boron-doped graphene has the characteristics of large specific surface area,high electrical conductivity and high electron mobility,and is one of the ideal materials for supercapacitor electrodes.Boron-doped diamond?BDD?has a wide potential window,low background current,high electrochemical stability and acid and alkali corrosion resistance.Therefore,the preparation of boron-doped graphene/boron-doped diamond?BG/BDD?electrodes has broad application prospects in energy storage devices.In this paper,BG/BDD electrodes were directly prepared by electron-assisted hot-wire chemical vapor deposition?EA-HFCVD?system.And we systematically studied the effects of graphene layer growth time and boron content on the morphology and electrochemical properties of BG/BDD electrodes.A symmetric supercapacitor?SSC?based on BG/BDD electrodes was constructed and its capacitance performance was tested.Combined with the scanning electron microscopy,it can be found that the graphene sheets grow vertically on the BDD and are in close contact with the BDD crystal plane.It was found by XPS and Raman analysis that boron atoms were effectively doped into graphene and diamond,and the content of boron in the graphene layer was between 1.04 and 2.45%.The BG/BDD composite electrode exhibits excellent capacitance characteristics in the saturated NaCl aqueous solution.When the graphene layer is grown for 30 s,the BG/BDD electrode has the largest volume capacitance(1047.8 F cm^-3).The boron content of the boron-doped graphene affects the BG/BDD-electrode performance,while the electrode has a high specific capacitance when the graphene is grown at a B-source-gas flow rate of 50 sccm.The SSC is subsequently fabricated with two BG/BDD electrodes,NaCl/CMC gel electrolyte and non-woven membrane to evaluate the practical application of the BG/BDD electrode.The BG/BDD-based device can operate at a high voltage of 3.2 V.The SSC delivers a high energy density of 79.5 Wh kg^-1 at a power density of 221 W kg^-1,and a high power density of 18.1 kW kg^-1 at an energy density of 30.7 Wh kg^-1;it also retains 99.6%of its specific capacitance in the 0-2.5 V(3.2 A g^-1,9000 cycles)voltage range,and 96.1%in the 0-3 V(12.8 A g^-1,10000 cycles)range.