Study On Electrochemical Energy Storage Of Porous Carbon Prepared By Recycled Polyimide

Carbon materials have been widely used in flame retardant,adsorption and separation,catalysis,electromagnetic wave absorption,energy storage and other fields,due to its large specific surface area,hierarchical porous structure,excellent electrical conductivity,simple production process and low preparation cost.Aromatic polyimides(PIs),as one kind of special polymer with excellent physical and chemical properties,has a great potential in the application of aerospace,high performance coatings,flexible electronic devices,microelectronic industry.However,it is still a challenge to recycling the completely imidized polyimide in an effective method due to their intrinsic insolubility and infusibility,resulting in serious environmental pollution.In this work,high value-added porous carbons were prepared from PIs to achieve effective recovery,and the electrochemical performance was studied in depth.(1)Hierarchical porous carbon was prepared by one-pot method by using polyimide(PI)as carbon precursor,N,N-dimethylformamide(DMF)as solvent,melamine polyphosphate and potassium oxalate as activator.The effects of the type and ratio of activators on the specific surface area,pore structure and electrochemical properties of porous carbon were discussed.The results showed that DMF solvent could change the morphology of porous carbon,and the synergistic action of melamine polyphosphate and potassium oxalate could cause loose porous structure(specific surface area:2080 m~2/g),in which relatively high proportion of micropores(the specific surface area and volume are 1828 m~2/g and 0.7493 cm~3/g,respectively)provided more active sites for ion adsorption.The nitrogen and phosphorus atoms doped not only improved the wettability of the interface between porous carbon materials and electrolyte,which made the porous carbon electrode material had high performance in electrochemical energy storage.The specific capacitance of porous carbon electrode could reach 317 F/g at 0.5A/g current density and provided an energy density of 15.6 Wh/kg.The capacitance retention rate of porous carbon electrode could still reach 92.3%even after 10000 cycles under 10A/g current density,showing excellent cycling stability.(2)PI,potassium oxalate and melamine polyphosphate were mixed at and dissolved in DMF with a weight ratio of 1:4:1,and graphene oxide(GO)was added with different quality to prepare hierarchical porous carbon.The effects of the ratio of PI to GO on the specific surface area,pore structure and electrochemical properties of porous carbon were discussed.The results showed that the addition of GO not only increased the ratio of mesopore(the specific surface areas of micropores and mesoporous/macropores were 1773 and 699.5 m~2/g,respectively),but also increased the specific surface area of the porous carbon material(2472m~2/g).Moreover,the addition of GO not only increased the content of oxygen in carbon materials,but also improved the wettability of the interface between the porous carbon and electrolyte and increased its pseudo-capacitance by redox reaction.The modified carbon materials showed specific capacitance of 406 F/g at 0.5 A/g current density and provided an energy density of 20.22 Wh/kg.Moreover,the modified carbon materials also showed an excellent cycling stability of 94.3%capacitance retention after 10000 cycles at 5 A/g current density.