Green Preparation Of Carbon Nanosheets From Rapeseed Cake And Their Electrochemical Properties

Supercapacitors with long cycle stability,high specific capacitance,safe and reliable characteristics have shown significant potential in the fields of energy storage.Porous carbon materials exhibit unique advantages when used as supercapacitor electrode materials due to their high specific surface area,excellent electrical conductivity,and good electrochemical stability.However,high production cost and complicated preparation process are the bottleneck problems that restrict further development and application of porous carbons.In this thesis,we have proposed a green,simple method to design and synthesize three-dimensional interconnected porous carbon nanosheets and the nitrogen and phosphorus co-doped carbon materials.The electrochemical properties of the as-preppared carbon materials are improved by functionalizing the surface and optimizing the pore structure of the carbon materials.The main conclusions are as follows:（1）Interconnected rapeseed cake-based porous carbon nanosheets（RSCs）were successfully synthesized from rapeseed cake using K₂CO₃ as activation agent by one-step carbonization activation method under nitrogen atmosphere.This method is simple and environment friendly.The pore structure of RSCs can be effectively regulated by changing the dosage of K₂CO₃.The RSCs possess large specific surface area(1647 m² g^-1)and big pore volume(0.98 m³ g^-1).As electrode materials of supercapacitor,RSCs exhibit high specific capacitance up to 223 F g^-1(0.05 A g^-1),excellent rate performance(152 F g^-1 at 100 A g^-1)and good cycle stability（97%capacitance retention after 10000 charge and discharge cycles）in a 6 M KOH electrolyte.（2）Based on the experiment（1）,the effect of nitrogen doping on the electrochemical properties of the carbon materials was investigated.Nitrogen doped interconnected rapeseed cake-based porous carbon nanosheets（N-RSCs）were successfully prepared from rapeseed cake using melamine as nitrogen doping agent coupled with K₂CO₃ activation.The mass ratio of carbon source to K₂CO₃ is 1/4.The as-made N-RSCs feature large specific surface area(2050 m² g^-1)and pore volume(1.13 m³ g^-1).In addition,the amount of nitrogen in N-RSC₂ is as high as 3.48%.As electrode materials of supercapacitor,N-RSCs exhibit high specific capacitance up to274 F g^-1(0.05 A g^-1),excellent rate performance(168 F g^-1 at 50 A g^-1)and good cycle stability（96%capacitance retention after 10000 cycles）in a 6 M KOH electrolyte.（3）On the basis of the experiment（2）,the effect of nitrogen and phosphorus co-doping on the electrochemical properties of the carbon materials was further studied.Nitrogen/phosphorus co-doped interconnected rapeseed cake-based porous carbon nanosheet（NP_w-RSC）was successfully prepared from rapeseed cake using melamine as nitrogen doping agent,phytic acid as phosphorus doping agent coupled with K₂CO₃ activation.The as-prepared NP_w-RSC possesses large specific surface area(1641 m² g^-1)and pore volume(0.83 m³ g^-1).In addition,the amount of nitrogen and phosphorus in NP_w-RSC is 2.36%and 2.44%,respectively.As electrode materials of supercapacitor,NP_w-RSC electrodes exhibit high specific capacitance up to 358 F g^-1(0.05 A g^-1),excellent rate performance(238 F g^-1 at 50 A g^-1)and outstanding cycle stability（103%capacitance retention after 10,000 cycles）in a 6 M KOH electrolyte.