Preparation And Capacitance Properties Of Coal-based Porous Carbon Spheres Doped With Heteroatoms

Because of its high chemical stability,light weight,good conductivity,adjustable pore structure and high specific surface area,the porous carbon materials is used as a support material or an electrode material in the filed of energy storage.The application of carbon-based porous electrode materials in electrochemical capacitors shows many advantages.However,pure porous carbon materials mainly rely on double-layer capacitors for energy storage,which have lower specific capacitance and lower energy density.Previous research results have indicated that the surface of carbon materials can be modified by heteroatom doping,the hydrophilic groups on the surface can be increased,change the surface functional groups,the wettability of electrolyte can be improved,and the pseudocapacitance can be introduced.But most of the carbon sources of porous carbon materials are expensive,and most of the precursor compounds containing nitrogen,sulfur,phosphorus and other heteroatoms also have certain toxicity.are also toxic to some extent.It is urgent to prepare porous carbon materials doped with heteroatoms with excellent properties by using cheap and widely available carbon sources and green non-toxic heteroatom sources.Among porous carbon materials with various morphologies,spherical carbon materials have attracted much attention due to their good dispersibility,strong fluidity,large specific surface area,good conductivity and abundant pore structure.Therefore,the coal of Xinjiang heishan was selected as the main raw material,adenosine triphosphate and L-cysteine,which are non-toxic,harmless and environmentally friendly biomolecules,were used as heteratomic sources to prepare heteroatom-doped coal-based porous carbon spheres by ultrasonic spray pyrolysis.The reasons for the different electrochemical properties caused by the differences of morphology,structure,doping content and doping form of the materials were also studied.The main research content and conclusion of this paper includes:?1?Coal-based porous carbon spheres were prepared by ultrasonic spray pyrolysis using water-soluble oxidized coal as precursors.The effects of pyrolysis temperature on the structure,morphology and electrochemical properties of carbon spheres were studied.The results show that the porous carbon spheres prepared at700^°C have the best electrochemical properties.In the three electrode system,when the current density is 1 A g^-1 and 10 A g^-1,the specific capacitance is 230 F g^-1 and128 F g^-1,respectively.?2?nitrogen and sulfur codoped coal-based porous carbon spheres were prepared by ultrasonic spray pyrolysis using water-soluble oxidized coal as carbon source and L-cysteine containing both nitrogen and sulfur functional groups was used as nitrogen source and sulfur source.By means of a simple ultrasonic spray pyrolysis method,nitrogen and sulfur codoped coal based porous carbon spheres were prepared.The morphology,structure and chemical composition of porous carbon spheres prepared at different feed ratios were studied,and the effects of these factors on the electrochemical properties of the materials were also investigated.When the ratio of coal oxide to L-cysteine is 3:1,the doping amount of nitrogen and sulfur in carbon spheres is the appropriate,showing excellent electrochemical performance,at the current density of 1 A g^-1,the specific capacitance was reached up to 308 F g^-1.After10000 cycles of cyclic charge and discharge at 5 A g^-1 current density,the specific capacitance retention rate is 90%,and it has good doubling performance.?3?Water-soluble coal oxide was used as carbon source,adenosine triphosphate as nitrogen source and phosphorus source.The effects of chemical composition,pore structure and specific surface area of carbon spheres prepared at different feed ratios on electrochemical properties were studied.The results show that nitrogen is successfully doped into carbon materials,but phosphorus is not successfully doped into carbon materials.When the ratio of soluble oxidized coal to adenosine triphosphate is 3:1,the nitrogen doping amount of carbon spheres is the highest and the electrochemical performance is the best,at the current density of 1 A g^-1,the specific capacitance was reached up to 282 F g^-1.After 10000 cycles of cyclic charge and discharge at 5 A g^-1 current density,the specific capacitance retention rate is 85%.