Study On Supercapacitance Properties Of Double Heteroatom Doped Graphene-supported Metal Compound Composites

Since the beginning of the information revolution in the 1990s,the explosive development of human society has put forward unprecedented and huge demands on energy.It is increasingly urgent to explore and develop new energy sources and energy storage materials.Graphene-supported metal compound composite electrode materials have great specific capacitance and high energy density because they combine the advantages of double layer capacitance and Faraday capacitance,and have promising prospects in the commercial application of supercapacitors.Therefore,we designed to combine the double-doped graphene with the metal compound material with high capacitance performance to investigate the energy storage performance of the composite.The main research work and results are as follows:1.The ammonium thiocyanate was used as a green nitrogen-sulfur source to simultaneously introduce N into GO and Fe₂O₃ by one-step hydrothermal method.A composite of N-Fe₂O₃ nanoparticles with uniform nitrogen-sulfur double-doped graphene?N-Fe₂O₃/NSG?with N as the junction was prepared.Due to the combination of the special structure of the doped oxide and the excellent conductivity of doped graphene,the N-Fe₂O₃/NSG nanocomposite electrode exhibited excellent electrochemical performance:the specific capacity measured at a current density of 1A g^-1 was 861.9 C g^-1,and the capacity retention was 91.3%after 5,000 cycles at 5 A g^-1.2.The practicability of bimetallic oxide loaded on sulphur-phosphorus double-doped graphene composite in the field of supercapacitors was explored.Cobalt and niobium,which had excellent performance in the field of supercapacitors,were selected as the metal sources for bimetallic oxides.CoNb₂O₆ nanoparticles with controllable particle size loaded with multifunctional sulfur-phosphorus double-doped graphene composite?CoNb₂O₆/SPG?were prepared by using phosphate to establish a stable connection between NbCo precursor and nitrogen-sulfur double-doped graphene.The CoNb₂O₆/SPG composite electrode exhibited a better specific capacity(667.3 C g^-1,1 A g^-1)and excellent rate characteristics(when the current density increased from 1 A g^-1 to 10 A g^-1,the capacity retention was 71.8%).In addition,the CoNb₂O₆/SPG electrode was used as the positive electrode and the activated carbon electrode was used as the negative electrode to assemble an asymmetric supercapacitor,which exhibited a wide operating voltage?0¹.6 V?,high cycle stability(capacitance retention is 92.5%after 10,000 cycles at current density of 1 A g^-1)and high power density(2995 W kg^-1,corresponding energy density is 39.7 Wh kg^-1)3.The supercapacitor properties of nanocomposites?Mn?PO₃?₂/NPG?formed by the combination of nitrogen-phosphorus double doped graphene and metal phosphate were studied.Ethylene glycol was used as a carbon source,and reacted with manganese acetate tetrahydrate,hexamethylenetetramine and phytic acid to synchronously generate thin layer of nitrogen-phosphorus double-doped graphene coated irregular porous Mn?PO₃?₂ nanosheets through simple hydrothermal and calcining method.Besides,the optimum calcination temperature in the synthesis route was emphatically studied.The irregularly overhead Mn?PO₃?₂ presented a three-dimensional structure,which provided criss-crossing electron transfer and ion transport channels together with the thin layer NPG.In addition,the micropores in the Mn?PO₃?₂ nanosheets further accelerated the transfer of charge,facilitating the passage of electrolyte ions,and improving electrochemical performance of the composite.The obtained composite materials were applied to a three-electrode system and a two-electrode system,exhibiting characteristics of large specific capacity(1241.1 C g^-1,1 A g^-1),long cycle life(capacity retention rate of 90.8%after 10,000cycles at 10 A g^-1),and high energy density(49.5 Wh kg^-1,the corresponding power density is 166.7 W kg^-1),further improving the cycle stability and power density of the electrode material,and widening the commercial application channel of the supercapacitor electrode material.