Electrochemical Properties Of Heteroatom Doped Graphene Hydrogels And Their Composites

Graphene is considered to be an ideal electrode material for supercapacitors due to its large theoretical specific surface area,good thermal conductivity and excellent mechanical properties.But the simple electric double layer capacitor of graphene and the single layer sheet structure are prone to occur agglomeration and stacking result in a decrease in surface area and ion conductivity,which limits its performance.Assembling the graphene sheets into a three-dimensional structure can effectively overcome the disadvantages of graphene stacking and agglomeration and increase its specific surface area.At the same time,doping of graphene with heteroatoms can effectively control the physicochemical properties of graphene,improving the electronic structure and improve the conductivity and redox activity of graphene.Those are the two main ways to improve the electrochemical performance of graphene.In this paper,self-made graphite oxide was used as raw material to synthesize three-dimensional graphene hydrogel by hydrothermal reduction.The three-dimensional graphene was doped with nitrogen,sulfur,phosphorus and other heteroatoms.The microstructure and electrochemical performance of different types of graphene materials were analyzed and compared.The effects of phosphorus content and different phosphorus sources on the electrochemical performance of graphene were studied and combined with nanostructured polyaniline in order to obtain electrode materials with excellent electrochemical properties.The main research contents are as follows:?1?Using graphite oxide as raw material,urea,p-toluene sulfonic acid and phytic acid as nitrogen,sulphur and phosphorus sources,Three-dimensional reduction of graphene oxide hydrogel?RGO?and three-dimensional reduction graphene oxide hydrogel doped with nitrogen,sulfur,phosphorus?RGN,RGS and RGP?were prepared by hydrothermal method.The microstructures and electrochemical properties of GO,RGO,RGN,RGS and RGP were tested respectively.The results show that heteroatoms such as nitrogen,phosphorus and sulfur are doped into the graphene lattice,and the doped graphene exhibits a honeycomb three-dimensional porous layered morphology.The Faraday tanta lum capacitors produced by heteroatom doping are beneficial to improve the electrochemical performance of three-dimensional graphene.Among them,the phosphorus-doped graphene electrode material has the best capacitance performance.In a 1 mol L^-11 H₂SO₄ electrolyte with a current density of 1 mA cm^-22 and a specific capacity of 388.5 F g^-1,Assembled into a symmetrical capacitor with an energy density of 25.2 Wh kg^-1 at a current density of 1 A g^-1.?2?Using graphite oxide as raw material and phytic acid,potassium dihydrogen phosphate and phosphoric acid as dopants,the effects of different phosphorus source dopants on the electrochemical properties of phosphorus-doped graphene were studied.Then,the effect of phosphorus content on the electrochemical properties of three-dimensional graphene was further studied with phytic acid as dopant.The results show that the graphenes doped by the three phosphorus sources exhibit excellent electrochemical performance,and the phosphorus-doped graphene prepared by phytic acid as a dopant?phosphorus doping amount is 0.94%?has a specific capacitance of 388.5 F g^-1,after circulating 10000 times at a current density of 3 mA cm^-2,the specific capacitance retention rate is 99.9%,and the electrochemical performance is optimal.This is mainly due to the large number of oxygen-containing functional groups carried by phosphorus atoms.Secondly,the C atom in phytic acid participates in the reorganization of graphene in the doping process,which also makes it show better electrochemical performance.?3?Polyaniline nanotubes were synthesized by emulsion polymerization.The preparation conditions were optimized,and the structure and electrochemical properties of the materials were tested.Using graphite oxide and polyaniline nanotubes as raw materials,urea,p-toluenesulfonic acid and phytic acid as dopants,three-dimensional graphene/polyaniline nanotubes doped with nitrogen,sulfur and phosphorus were synthesized b y one-step hydrothermal method.The structure and electrochemical properties of the composites were tested.The specific capacitance ofthe phosphorus-doped three-dimensional graphene/polyaniline nanotube composite is 593 F g^-1,the retention rate of 2000 cycles is80.7%,and the current density increases from 0.5 A g^-1 to 5 A g^-1,The specific capacitance retention rate is still up to 82.2%.It is assembled into a symmetrical capacitor with an energy density of up to 45 Wh kg^-1.