Aqueous Supercapacitors Based On Boron-Doped Graphene/BDD/TiO₂ And Boron-Doped Graphene/BDD

Boron-doped graphene has a large specific surface area,high carrier mobility,excellent electrical conductivity and good charge storage.It is one of the ideal materials for supercapacitor.Boron-doped diamond has many advantages,such as wide potential window,low background current,high electrochemical stability,and so on.One-dimensional titanium dioxide nanotubes have the characteristics of large specific surface area and fast electron transfer speed.Therefore,a boron-doped graphene(BDG)/boron-doped diamond(BDD)cathode and BDG/nanocrystals(NBDD)/TiO₂ nanotube array anode can improve the specific capacitance,cycle stability and rate performance of supercapacitors.In this paper,TiO₂ nanotube arrays are prepared by electrochemical anodization,and BDG and BDD are prepared by electron-assisted hot-filament chemical vapor deposition(EA-HFCVD).Thus,boron-doped graphene(BDG)/boron-doped diamond(BDD)cathodes and BDG/nanocrystals BDD/TiO₂ nanotube array anodes are prepared and tested for their capacitance performance in aqueous sodium and lithium ion solutions(SIC and LIC).In order to increase the working voltage,energy density,and power density,aqueous sodium-ion capacitors(SIC)and lithium-ion capacitors(LIC)are constructed by constructing appropriate electrode materials.Vertically grown BDG nanosheets form a porous three-dimensional morphology with short ion diffusion distances,rich charge storage sites,and high structural stability.In aqueous Na Cl solution,the potential windows are 0-1.1 V and-1.2-0 V for the cathode and anode,respectively,and their specific capacitances are 66.76 and 23.86 mF cm^-2 at a current density of 3 mA cm^-2.Asymmetric supercapacitors constructed with BDG/BDD cathodes and BDG/NBDD/TiO₂anodes exhibit high energy density(SIC:47.8?Wh cm^-2;LIC:33.9?Wh cm^-2)and high power density(SIC:77.7 m W cm^-2;LIC:65.3 m W cm^-2)at an operating voltage of 2.5 V.The SIC and LIC achieve 100% coulombic efficiency over 10,000 cycles,with capacitance retention of 99.5%and 97.8%,respectively,at a high current density of 90 m A cm^-2 over 2,000 cycles.Moreover,the capacitors exhibit effective AC current filtering over a wide frequency range of 50-10,000 Hz.The coulombic efficiencies and long-term stabilities of these aqueous devices are better at high current densities,while retaining large energy densities at high power density,which is advantageous for high frequency filtering.