Hydrothermal Synthesis Of Porous Carbon Microspheres And Their Electrochemical Performance

Carbon microspheres?CMS?are a kind of functional carbon materials with regular spherical structure.The particle sizes of CMS are in a range from several nanometers to dozens of micrometers.They not only have unique morphology,but also have some special properties including thermal and chemical stabilities,electrical and thermal conductivities and so on.Although synthesis methods such as templating,chemical vapor deposition and other methods can prepare CMS with different sizes and structures,the preparation processes of those methods are usually complicated with high energy consumption.Hydrothermal method is simple whithout pollution to the environment.However,the specific surface area of obtained product via hydrothermal method is relatively low.With the development of technology and the increasing demand of mankind,carbon materials need greater specific surface area and more suitable pore structure,especially as electrode material of supercapacitors.Porous carbon microspheres?PCMS?with abundant pore structures and high surface area can be obtained after the activation of CMS.In this paper,PCMS were synthesized by simple hydrothermal carbonization of water-soluble starch and subsequent environmentally friendly CO₂ activation method.In order to find the optimal synthesis route and explain the impact of various factors on the final performance of obtained sample,the effects of different activation conditions and different hydrothermal conditions on the electrochemical properties were investigated.PCMS were systematically characterized by using XRD,SEM,BET,FT-IR,GCD,CV and EIS.The results show that CMS synthesized by hydrothermal method exhibit good spherical morphology with particle size ranging from 0.5 to 5 ?m.After CO₂ activation,the spherical structures of PCMS have not been destroyed with significant increase in specific surface area.Pore sizes produced are mainly around 1.6².1 nm,and the graphitization degree of PCMS is enhanced simultaneously.PCMS obtained after CO₂ activation for 9 h at 1000 oC shows the best supercapacitive performance.The best hydrothermal temperature,hydrothermal time and solid-liquid ratio are 190 oC,12 h and 0.1,respectively.Electrode material prepared under the best conditions of activation and hydrothermal method has the best electrochemical performance.The highest specific capacitance of PCMS electrode reaches 176 F/g at 50 mA/g of current density.