Preparation And The Study Of Capacitive Properties Of Carbon Cloth Supported Transition Metal Nitrides

Due to the co-existence of ionic,covalent,and metallic bonds,transition metal nitrides exhibit a variety of physical and chemical properties,such as polycrystalline structure and valence states,excellent electrical conductivity,and can provide abundant redox sites for improving electrochemical activity.Transition metal nitrides show excellent conductivity,thermal stability,theoretical high capacity,and excellent electrochemical activity in supercapacitors,but their small specific surface area,poor stability in the cycle,and collapsible structure make them unable to be effectively applied in supercapacitors.Carbon-based materials with large surface area,good conductivity,and strong stability are usually used as electrode materials for electrical double-layer capacitors.In this paper,transition metal nitride is grown on carbon cloth as the electrode of flexible supercapacitor.The morphology,structure,and composition of the product are characterized by scanning electron microscopy（SEM）,X-ray photoelectron spectroscopy（XPS）,powder X-ray diffraction（XRD）,etc.The product could be successfully applied in flexible supercapacitor.The results of electrochemical experiments show that the composites have high theoretical capacity and conductivity,and maintain high cycling stability in long cycles.The main work of this paper is summarized as follows:1.Using zinc nitrate hexahydrate,cobalt nitrate hexahydrate,and dimethylimidazole as raw materials,a scalable metal-organic framework（MOF）assisted strategy is selected to prepare a double-layer Zn-ZIF@Co-ZIF/CC precursor array using carbon cloth as the substrate by simple epitaxial growth method.The double-layer zeolite imidazole acid frame array is used as the precursor to construct a nanosheet array on carbon cloth.Further high-temperature nitriding treatment obtains Co_5.47N/CC.The size and morphology of the final product can be controlled by controlling different nitriding temperatures and time.The area capacitance can reach 281.03 mF·cm^-2 at a current density of 0.5 mA·cm^-2,and the retention rate of area capacitance is 92.0%at a current density of 0.5 mA·cm^-2.When two identical Co_5.47N/CC electrodes are assembled into a completely symmetrical solid-state flexible supercapacitor,the area-specific capacitance reaches 33.43 mF·cm^-2 at a current density of0.1 mA·cm^-2,and the capacitor has good long-term cycle stability.Bending experiments show that the device has excellent flexibility.2.A carbon cloth supported nitride heterostructure is designed and prepared.The composite material of nickel-vanadium layered double hydroxide precursor and carbon cloth is prepared by the one-step hydrothermal method.After the material is treated under different nitriding conditions,the carbon cloth supported layered nickel-vanadium nitride heterojunction electrode material is obtained.The carbon cloth supported bimetallic nitride electrode material is obtained by treating the precursors under different nitride conditions.The electrochemical experimental data show that the best material is prepared when the nitriding temperature is 400℃and the nitriding time is 2 hours.The specific capacitance of the VN/Ni₃N-Ni/CC electrode can reach 845.63 mF·cm^-2 at a current density of 0.5m A·cm^-2 under the optimal conditions,and the retention rate of the area capacitance is 86.1%after 1500 cycles at a current density of 10 mA·cm^-2.The capacitance performance of the flexible all-solid symmetric supercapacitor assembled with VN/Ni₃N-Ni/CC electrodes is studied.The area-specific capacitance is 19.1 mF·cm^-2 at a current density of 0.5 mA·cm^-2.In order to satisfy the practical application of flexible energy storage devices,two identical capacitors are connected in series and parallel,and the results show that the capacitor follows the law of series and parallel well.