Synthesis Of Porous Carbon By A Dual Activation Method For High-performance Supercapacitor Application

The porous carbon electrode materials prepared using biomass as carbon source have the advantages of vastly specific surface area and reasonable pore structures,providing a large number of electrochemical active sites for charge storage.However,the small effective specific surface area,the unreasonable pore size distribution,and the low structural stability of the reported porous carbon electrode materials constrict their practical application in the field of supercapacitors.In order to solve the above challenges,besides selecting suitable biomass carbon source,a more important strategy is to optimize the porous carbon preparation technology.In this dissertation,preparation and supercapacitor applications of porous carbon using puffed rice as carbon source under different activation methods were investigated.In particular,a dual activation method was proposed to produce three-dimensional honeycomb structured porous carbon material with reasonable pore size distribution,ultrahigh specific surface area,and excellent electrochemical properties for high-performance supercapacitor application.Firstly,puffed rice was used as carbon source to prepare porous carbon material by a potassium permanganate solid-template method.Potassium permanganate not only provided template for the formation of porous carbon but also activated the carbon material.The obtained sample was revealed to be nitrogen and oxygen co-doped carbon.Using the porous carbon as the electrode material,a high capacitance value of 235.5 F?g^-1 was achieved in a three-electrode system.The graphitized structures maintained the porous structures of the related electrode material even at high current densities.Secondly,three-dimensional porous carbon material was prepared by employing potassium hydroxide to activate the puffed rice.The resulted carbon material was revealed to contain some oxygen-related functional groups with large specific surface area.The electrochemical measurements showed that the potassium hydroxide-induced porous carbon present higher capacitance performance than the porous carbon prepared by the solid template method,exhibiting a capacitance value of 399 F?g^-1 as the electrode material in a three-electrode system.Finally,the puffed rice was activated by a dual activation method using potassium permanganate and potassium hydroxide simultaneously to prepare three-dimensional honeycomb-structured porous carbon material.The honeycomb-structured porous carbon was characterized to be nitrogen and oxygen co-doped carbon materials with reasonable pore size distribution,ultrahigh specific surface area and excellent electrochemical performance.Its capacitance performance and cycling stability are far superior to the porous carbon prepared by the potassium hydroxide activation method and the solid template method.In a three-electrode system with potassium hydroxide as the electrolytic solution,the capacitance of the porous carbon material produced by the dual activation method was as high as 676 F?g^-1.As for the supercapacitor application using potassium hydroxide electrolyte,an ultrahigh capacitance value of 409 F?g^-1 was achieved.Additionally,an energy density as high as 123.7Wh?kg^-1 was verified in ionic liquid EMIMBF₄ electrolyte.