Preparation By Template Method And Supercapacitive Capabilities Of CTFs Nanosheets

Supercapacitors,as one of the most promising electrochemical energy storage systems,have attracted tremendous attention due to their fast charge-discharge capabilities,excellent cycle stability,and high power density.Generally supercapacitors are mainly composed of electrodes,electrolytes and separators.Electrode materials has major role on the electrochemical performance of supercapacitors.Heteroatom-doping,pore engineering and nano-morphology control are necessary for the preparation of high supercapacitive performances electrode materials.Covalent triazine frameworks(CTFs)have recently been viewed as the most outstanding candidates for controllable preparation of electrode materials with high capacitance performance,owing to adjustable composition and structure,rich nitrogen content,high specific surface area,good stability,and easy functionalization.In this thesis,the fabrication of CTFs nanosheet-based electrode materials by ion-thermal method with Si O₂-templated triazine-based compounds as the monomer.The supercapacitive performances of these CTFs nanosheet electrodes have also been investigated based on their compositions and structures as well as morphology control.The main research work includes:(1)Template synthesis of TAT-based CTFs nanosheets for high performance supercapacitors.Firstly,the Si O₂-templated triazinyl compounds monomer(Si O₂-TAT)was synthesized from 4-Aminobenzonitrile and cyanuric chloride as raw materials and silica nanospheres as template.Subsequently,a series of TAT-derived CTFs nanosheet materials(TAT-CTFs)were prepared through Zn Cl₂-mediated cyclotrimerization by stepwise heating method using Si O₂-TAT as monomer.The TAT-based CTFs material(TAT-CTF-600)was synthesized under the optimum polymerization temperature possessed a nanoparticle aggregated nanosheets structure,relatively high specific surface area(203 m² g^-1),appropriate pore size distribution(2-10 nm)and high nitrogen content(12.83 wt%).Owing to these merits,TAT-CTF-600 electrode material exhibited a high specific capacitance of 220 F g^-1 at current density of 0.5 A g^-1 in 6 M KOH electrolyte.The TAT-CTF-600-based supercapacitor achieved relatively high energy density(10.1 Wh kg^-1)and power density(16.0 k W kg^-1),as well as long cycle life(89.95%of capacitance retention,after 10,000 charge and discharge).(2)Template synthesis of TOT-based CTFs nanosheets for high capacitance performance supercapacitors.The Si O₂-templated triazinyl compounds monomer(Si O₂-TOT)was synthesized from 4-Hydroxybenzonitrile and cyanuric chloride by using Si O₂ nanospheres as template.The TOT-derived CTFs nanosheet materials(TOT-CTFs)then were prepared through ion-thermal method using Si O₂-TOT as monomer.The TOT-based CTFs material under optimal conditions(TOT-CTF-600)possess 2D nanosheets structure(with thickness of 20-30 nm),high specific surface area(203 m²g^-1),and abundant nitrogen(11.67 wt%)and oxygen contents(13.12 wt%).Due to these merits,TOT-CTF-600 electrode material displayed both high gravimetric capacitance(250 F g^-1 at 0.5 A g^-1)and superior rate performance(174 F g^-1 at 20 A g^-1)in the 6 M KOH electrolyte.Moreover,the TOT-CTF-600-assembled symmetrical supercapacitor achieved long-term cyclability(88.56%retention after 10000 cycles in1 A g^-1).