Preparation And Electrochemical Properties Of Carbon Foam Based Carbon Electrode Materials

Carbon materials are the earliest industrial production and have been used in supercapacitor electrode until now due to the high specific surface area and excellent cycle stability.As a typical 3D network porous carbon material,carbon foam shows great potential in supercapacitors,lithium ion batteries and other fields.However,due to the limitation of traditional template method,the pore size distribution of carbon foam is narrow,which mainly are micron size pores?100-200?m?.Hence,the specific surface area is too low to provide enough charge capacity for supercapacitors.Therefore,from the point of preparation technology of carbon foam,improving the pore size distribution and modifying the micron pore to enhance the specific surface area is the key to realize the application in supercapacitors.Based on the above statement,this thesis employed the multi pore size liquid foam as soft template,combined with microwave curing technology and freeze-curing technology to fabricate hierarchical porous carbon foam.Then,the catalyst precursor and graphene oxide was introduced into resin in the preparation process of carbon foam.Through high temperature catalytic treatment and hydrothermal method,carbon nanotubes and graphene aerogels was synthesized in the pores of carbon foam to modified micron size pores and improve specific surface area.The results are as followed:?1?Using liquid foam as soft template,microwave-curing carbon foam?W-CF?and freeze-curing carbon foam?F-CF?were successfully prepared by microwave curing technology and freeze-curing technology.The effect of carbonization temperature on the structure and electrochemical performance of W-CF and F-CF was studied systematically.The results show that both W-CF and F-CF retained the original multi-size pore distribution structure of the liquid foam with a large number of nano-pores formed on the inner wall of the carbon foam originated from cracking of the resin.With the carbonization temperature increased,the specific surface area and specific capacitance of W-CF and F-CF show a decreased trend.When the carbonization temperature was 800?,the specific capacitance of W-CF and F-CF reached the maximum value of 135.5 F/g and 120.9 F/g at a current density of 0.5 A/g,respectively.?2?Based on the results of?1?,the Ni?NO₃?₂·6H₂O was used as catalyst precursor in the preparation process.The 1D carbon nanotubes were in-situ grown on the pore wall of carbon foam at high temperature to modify the pore structure.The results show that the W-CF/CNT still kept a hierarchical porous structure.As the carbonization temperature increased,the microporous and mesoporous content increase,which lead to the increased specific surface area and average pore diameter,thus leading to the enhancement of the specific capacitance.However,the resistance decrease with the carbonization temperature increased.When the amount of catalyst increased,the number of carbon nanotubes increased,but the specific surface area and specific capacitance.When the carbonization temperature is 1200? and the catalyst is 1wt%,W-CF/CNT acquired the maximum specific surface area and specific capacitance with the value of 277.4 m²/g and 53.1 F/g,respectively.When the carbonization temperature increase,the specific surface area and average pore diameter of F-CF/CNT increased slightly,but the specific capacitance decreased with the resistance increased.When the amount of catalyst added to 2wt%,the number of carbon nanotubes in F-CF/CNT increased,the specific surface area and specific capacitance of the carbon foam are all improved.When the carbonization temperature is 1000? and the amount of catalyst is 2wt%,F-CF/CNT acquired the maximum specific surface area and specific capacitance,which was 160.5 m²/g and 66.1 F/g,respectively.?3?Based on the results of?1?,graphene aerogels modified carbon foam materials were prepared by template method and sol-gel method respectively.The structure and electrochemical performance of the carbon foam were studied systematically.The results show that for the graphene aerogels modified carbon foam?W-CF/GA1 and F-CF/GA1?prepared by the template method,graphene aerogels were filled into the pores of the carbon foam,which modified the micron size of pores and increased the graphitization degree of carbon foam.The specific surface area was significantly increased,resulting in improved electrochemical performance.The specific surface areas of W-CF/GA1 and F-CF/GA1 were 559.7 m²/g and 981 m²/g,respectively,and the specific capacitance were 158 F/g and 178.5 F/g at 0.5 A/g.For graphene aerogels modified carbon foam?W-CF/GA2 and F-CF/GA2?prepared by sol-gel method,graphene aerogels are also filled into the pores of carbon foam,graphene aerogels were connected tightly with the carbon foam.Hence,the pore structure of the carbon foam is modified and improved and the graphitization degree of the carbon foam also increased.As a results,the specific surface area and the specific capacitance of W-CF/GA2 and F-CF/GA2 increased significantly,and the resistance of the electrode is reduced.The specific surface areas of W-CF/GA2 and F-CF/GA2 were 785.8 m²/g and 737.6 m²/g,respectively,and the specific capacitances were 211 F/g and 210.5 F/g at 0.5 A/g,respectively.