Synthesis And Electrochemical Performance Of Porous Carbon/Pseudocapacitance Composite Electrode Materials

Carbon materials are widely used in supercapacitor electrode materials due to their high specific surface area,high electrical conductivity,and excellent physical and chemical stability.However,the capacity of carbon materials mainly comes from electric double layer capacitors with limited energy density.In comparison,pseudocapacitance materials can store a large amount of charge through redox reaction,which has a higher energy density,but it also has problems such as poor structural strength and conductivity,which limits its full performance.One of the ways to improve this situation is to combine the pseudocapacitance materials with the carbon materials to make a composite electrode material with the advantages of both materials.In this paper,mesoporous carbon microspheres(MCMs)made from spray drying were used as carbon skeleton,and pseudocapacitance/mesoporous carbon composites were prepared by introducing pseudocapacitance materials into pores of MCMs.The electrochemical properties of the composite materials were studied systematically by using the standard three electrode system,and the structure and electrochemical properties of mesoporous carbon materials after the introduction of pseudocapacitance materials were analyzed in depth.The main conclusions of this paper are as follows:(1)mesoporous carbon microspheres(MCMs)with mesopore structure were prepared by spray drying method using phenolic resin as carbon precursor and silica sol as template.PANI/MCMs composite was prepared by chemical oxidation polymerization of polyaniline(PANI)in MCM pores using ammonium persulfate as initiator.The high pseudocapacitance of PANI can greatly improve the specific capacitance of the composite,in 1 M H2SO4 electrolyte and at the current density of 1 A g-1.The specific capacitance is 435 F g-1,which is much higher than the 184 F g-1 of MCMs under the same conditions.At the same time,due to the proton conductivity of PANI,the capacity of PANI/MCMs at the current density of 20 A g-1 is 83%of that at 0.5 A g-1,showing an excellent rate performance.PANI in pores does not significantly hinder the reactivity of internal PANI,and the material density was increased.Therefore,the composites have excellent volumetric capacitance,up to 539 F cm-3,which is significantly higher than 127 F g-1 of MCMs.In addition,PANI/MCM composites exhibited good cycling stability,retaining 84%of the capacitance after 1000 charge/discharge cycles at 1 A g-1,owning to the close combination of PANI and MCMs(2)MnO2/MCM composite was synthesized by the reaction of KMnO4 and MCMs.The uniform nano channels of MCMs confine MnO2 to nano scale and provide conductive network for MnO2.Therefore.MnO2/MCMs have excellent electrochemical performance.In 1 M Na2SO4 electrolyte and at the current density of 1 A g-1 the specific capacitance is 188 F g-1,which is much higher than 93 F g-1 measured by MCMs under the same conditions.In addition,MnO2,as a transition metal oxide,has a high density and pseudo capacitance.The introduction of MnO2 into MCMs pores can make the composite having a high volumetric capacitance,up to 347 F cm-3.Due to the close combination between MnO2 and MCMs,at the current density of 1A g-1,MnO2/MCMs can maintain 90%of the original capacity after 1000 times of charge/discharge cycles.Different from PANI,MnO2 does not have proton conductivity,a moderate increase in the amount of MnO2 can improve the specific capacitance of the composite,while too much MnO2 will block the channels,reduce the internal MnO2 reaction activity,and reduce the electrochemical performance.