Study On Preparation And Electrochemical Properties Of Nitrogen-Doped Porous Carbon Materials

With the increasing energy crisis and environmental pollution,people urgently need a green,safe and highly-effective new energy storage device,so electric double layered capacitor（EDLC）has attracted extensive attention as one kind of fast energy storage and conversion device due to its high power density,better rate capability and long cycle life.As the core of supercapacitor,the preparation and electrochemical property of electrode materials are very important.Porous carbon materials are attractive owing to their remarkable advantages such as high surface area,small ion diffusion resistance and large controllable inner pore volume,so it has great development prospects in the application fields of EDLCs electrode materials.Therefore,this article utilize PDA as carbon source and ZnO as template to prepare nitrogen-doped porous carbon materials with different morphologies and use it as electrode material for EDLCs.The main research work includes the following two sections:（1）This chapter reports a surfactant-assisted template method to synthetize hollow carbon spheres by utilizing PDA as carbon source and ZnO as sacrificing template.First,spherical ZnO nanoparticles were synthesized with the help of surfactant（Triton X-100）.Then,the dopamine monomer was polymerized to form a PDA film and covered on the surface of ZnO at room temperature.After carbonization in N₂ atmosphere followed by HCl etching,hollow carbon spheres with adjustable particle size（150³00 nm）,high specific surface area(SSA,¹100 m² g^-1)and optimized mesopore size distribution are obtained.The addition of nonionic surfactant could not only help formation of the ZnO nanospheres,but also protect amphoteric ZnO template from dissolving by the alkaline conditions needed for self-polymerization of dopamine.In order to obtain hollow carbon spheres with controllable structure and excellent electrochemical performance,we have investigated the effects of surfactant content,loading time and carbonization temperature on the morphology and the electrochemical properties of the as-prepared carbons.Studies have shown that the synthesized hollow carbon spheres exhibit better electrochemical performance under the conditions of a surfactant dosage of 2 mL,a loading time of 48 h and a temperature of 800℃.The optimum sample presented the better rate performance with specific capacitance of 156 F g^-1 at the scan rate of 2 mV s^-1 and 125 F g^-11 even at the scan rate of 200 mV s^-1 and excellent cycling stability of exceeding 98%capacitive retention after 16,000 cycles.In order to further improve capacitance performance of the electrode materials,we prepared GO/hollow carbon sphere composites and explored the effects of graphene dosage on composites morphology and electrochemical performance.The result shows that composites with graphene dosage of 6.8 mg has a high specific capacitance of 195 F g^-1 at 2 mV s^-1.（2）Nitrogen-doped carbon materials with a 3D micro-flower structure was prepared by using PDA as carbon source,flower-like ZnO as template and urea as nitrogen source.The effects of urea dosage,polydopamine quality and loading time on the nitrogen-doped carbon materials with morphology,structure and electrochemical properties were investigated.The results show that the prepared nitrogen-doped carbon micron flower has a hierarchical porous structure composed of interconnected macropores,mesopores and micropores.Moreover,with the urea dosage increases,the specific surface area of the carbon materials increases.Under the conditions of urea dosage of 1.4 g,polydopamine mass of 0.4 g and a loading time of 24 h,the prepared carbon material obtains high nitrogen content of 12.6%,specific surface area of 666 m² g^-1 and the specific capacitance of 187 F g^-1 at 1 A g^-1.The capacitance retention is 92%after 10,000 cycle numbers and indicates that the sample possesses remarkable cycling stability.