Preparation Of Polyimide-based Activated Carbons With High Surface Area And Their Electrochemical Performances

As a new type of high performance polymer material,polyimide(PI)films are widelyused in aerospace,military,electronics,environmental protection and new energy and other fields.With PI film production in China increased year by year,and the use of a large number of offcuts has become one of the urgent problems in the process of production.Currently,the main treatment methods are alkali degradation,incineration or landfill,which is not only a waste of resources,but also may cause secondary pollution to the environment.In order to realize the resource utilization of PI film offcuts,using carbonized PI film as the precursor,activated carbons with high surface areas have been prepared by physical or KOH chemical activation method,their electrochemical performances have been investigated thereafter.The adsorption properties,pore structure and surface properties of resulted activated carbons were characterized by adsorption test,nitrogen adsorption,XRD and XPS techniques;the preparation method and the corresponding activation parameters influence on adsorption properties and pore structure of activated carbons have been investigated,the manufacture process has been optimized,and the activation mechanism has been discussed also;influence of pore structure,surface chemistry and preparation method on their electrochemical performances have been investigated as well.The main results are as follows:(1)The activation process has a significant effect on the adsorption,pore structure and surface properties of activated carbon.The adsorption capacities of activated carbons on iodine,benzene and methylene blue could be enhanced by prolonging the physical activation time or increasing the ratio of KOH to carbonized PI film.The activated carbons with high porosity and high specific surface area can be prepared by both physical activation and KOH chemical activation,the specific surface area exceeds 2800m2/g with the pore volume over1.4cm3/g.The pore structure and the surface properties of activated carbon varied with different activation methods: activated carbon prepared by physical activation possess a wider pore size distribution and more nitrogen-containing surface groups;while the KOH activated carbon display a more narrow pore size distribution,and the surface nitrogen content decreased sharply with increasing the ratio of KOH to carbonized PI film.(2)The texture properties of activated carbon have a significant effect on its electrochemical performance.Generally,the specific capacitance of activated carbonincreases with the increase of specific surface area,but the relationship between them is not linear.Moreover,the specific capacitance has been found associated to the pore size distribution and surface chemistry.The activated carbons prepared by both physical and KOH activation methods exhibited excellent electrochemical performances.Due to a higher specific surface area,a larger pore volume,a relative narrower pore size distribution and more hydrophilic oxygen-containing groups favored to pseudocapacitances,activated carbon prepared by KOH activation exhibits an improved electrochemical properties.The mass specific capacitance of activated carbon prepared by physical activation method can reach237F/g,and the capacitance retention rate is 86%;the mass specific capacitance of activated carbon prepared by KOH activation method can reach as high as 482F/g,and the capacitance retention rate is about 62%.