Study On The Thermochemical Preparation And Directional Modification Of Rapeseed Meal-based Self-doped Capacitive Carbons

Rapeseed meal,as a waste biomass in the process of industrial production of rapeseed oil products,is resource intensive and has a high content of nitrogen,phosphorus,and sulfur elements,which has the potential to prepare carbon materials with both porous structure and rich surface chemical characteristics through thermo chemical conversion technology,and is of great value for exploring new types of biomass based supercapacitor capacitive carbons.Based on this,in this thesis,rapeseed meal is selected as precursor to explore its thermo chemical conversion to form char material structural characteristics and its electrochemical performance as supercapacitor capacitor carbon,first to study the effect mechanism of activation temperature of potassium hydroxide（KOH）on the doping process,second to explore the effect of carbonization way on the functional groups of heteroelements through the regulation of precarbonization way,and finally to make nitrogen and phosphorus element doping strengthening through melamine and potassium dihydrogen phosphate,The mechanism of action of heteroatomic functional groups on the modification of carbon matrix structure was realized.This thesis specifically works as follows:（1）In this study,the characteristics of rapeseed meal based self doped N-S porous capacitive carbons prepared by two-step process of carbonization and activation at high temperature were investigated by using KOH as activator and rapeseed meal as biomass precursor,then the effect of three different activation temperatures（600,700 and 800℃）on the pore gap structure of rapeseed meal based activated carbons was investigated,and the effect mechanism of activation process on heteroelement doping was characterized and analyzed.The results showed that low-temperature activation at 600℃was beneficial to the retention of the structure of the heteroelement functional groups in biomass to obtain carbon samples rich in N and S,but the pore structure of the samples was not sufficiently activated and the specific surface area was relatively small,and the sample mass specific capacitance was 214.1 F g^-1;The activation temperature of 800℃is the most unfavorable for the retention of heteroelements,although the specific surface area of the samples can reach 3526.6 m²g^-1after activation,but the contents of N and S elements are only0.81%and 0.69%,respectively;The sample at an activation temperature of 700℃possesses both good pore structure and abundant surface heteroelement functional groups,thus presenting the best electrochemical characteristics,and the mass specific capacitance can reach 303.4 F g^-1at a current density of 1 A g^-1.（2）In this study,the effect of thermochemical preparation method on the structural and surface chemical characteristics of rapeseed meal based capacitive carbon was investigated to achieve the fabrication of both rich surface heteroelement groups and micro mesoporous connected structured capacitive carbon.The results show that when high-temperature carbonization is chosen as the pretreatment step,the as prepared samples RM@HTC The specific surface area reaches 3283.2 m²g^-1,and the relative contents of N and S functional groups reach up to 1.49%and 1.01%,respectively,and the related structures not only provide ample space for the massive storage of ions and electrons,but also enable the introduction of functional group structures to optimize the material surface infiltration and introduce pseudocapacitance.Based on capacitive carbon RM@HTC as prepared electrode material,the mass specific capacitance reaches 303.4 F g^-1at a current density of 1 A g^-1and still retains 210.0 F g^-1when the current density is lifted to 10 A g^-1.In addition,the material has a power density of 625 W kg^-1and an energy density of 9.0W h kg^-1.Excellent cycling stability is exhibited with a capacitance loss of only 7.1%over 10000 charge discharge cycles at a current density of 10 A g^-1.（3）Studied the characteristics of N-P groups on the surface of capacitive carbon modified by high temperature carbonization,Koh activated coupled with potassium dihydrogen phosphate and melamine co doping directed strengthening to further improve the pore structure of carbon materials.The as prepared carbon samples are further strengthened by the introduction of potassium dihydrogen phosphate and melamine to etching carbon materials（RM@NP）The specific surface area reaches3865.7 m²g^-1,and the relative contents of N and P elements on the surface are 2.32%and 0.17%,respectively.As electrode materials,RM@NP The mass specific capacitance reaches 460 F g^-1at a current density of 1 A g^-1,the specific capacitance is344.3 F g^-1at a current density of 10 A g^-1,and the capacitance retention is 75%.When the energy density was raised to 10.1 W h kg^-1,the power density was 625 W kg^-1.Furthermore the capacitive carbon also exhibits excellent cycling stability with83.9%capacitance retention after 10000 cycles.