The Preparation Of Heteroatom Doped MXene And Its Application In Supercapacitor

In recent years,two-dimensional materials have shown great application potential and broad development prospects in the fields of flexible wearable devices and portable electronic products with their controllable electronic structures,large surface area and flexible layered channels.The discovery of graphene in 2004 provoked arrogance in the scientific community,which opened the door to the world of two-dimensional materials.As science and technology enters the“post-graphene age”,new two-dimensional materials such as transition metal sulfur/oxide,transition metal carbon/nitride,hexagonal boron nitride,borene,silene,phosphoenene,and terpenes,etc.have been emerged.Among them,two-dimensional transition metal carbide/nitride?MXene?materials have become a research hotspot due to their magnetic properties,mechanical and excellent electronic,and have important application value in the field of energy storage.Compared with the carbon materials used in traditional supercapacitors,MXene materials have the advantages of higher stacking density,better electronic conductivity and stronger charge storage capacity per unit volume,which make MXene materials have high capacity in the field of supercapacitors.However,the study found that MXene interlayer energy storage field can't fully play its role because of its has a large surface energy,causing aggregation and stacking between interlayers,resulting in g a significant reduction in the exchange efficiency of electrolytes,and seriously restricts the electrochemical utilization of MXene sheet.In order to further improve the electrochemical properties of MXene materials,heteroatom doping?nitrogen,sulfur,boron,phosphorus?is an effective method.Up to now,there have been few studies on the application of heteroatom doping to the modification of MXene.In this paper,we improve the specific capacitance of MXene by doping heteroatoms and study its application in the field of micro supercapacitors.This paper is divided into five parts:In the first chapter,the research background of MXene is introduced,and the preparation methods,properties,applications of MXene are reviewed.In addition,the related structure and design of microcapacitors are reviewed,and the main contents of the research purpose and work of this paper is put forward.In the second chapter,the Ti₃Al C₂ MAX phase ceramic was employed in the raw material,HF and HCl-Li F were used as the etching agent for chemical etching to obtain a multilayer MXene structure similar to expanded graphite.Dimethyl sulfoxide?DMSO?was applied to intercalation agent to separate stacked MXene phase,and the multilayer MXene was separated by ultrasonic treatment to obtain a macroscopically controllable,high-quality monolayer MXene.A flexible self-supporting paper electrode supercapacitor was prepared using MXene solution,which has an super high volume capacitance?achieve 238.5 F/cm³ at a scan rate of 2 m V/s?,excellent flexibility and stability.In the third chapter,make further efforts improve the electrochemical performance of MXene,with ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate as a heteroatom-doped N and B sources,a new type of N,B-doped MXene?N,B-Ti₃C₂T_x?was synthesized by heat treatment of MXene at different temperatures,and used as active materials for supercapacitor.The influence of annealing temperature to electrochemical performance was studied,and the results indicate that the capacitance performance is effectively improved at calcination temperature of 300oC.The mass capacitance of N,B-Ti₃C₂T_x-300oC was measured to be 65 F/g at scan rate of 100 m V/s,which is 5.5times higher than that of Ti₃C₂T_x.The EIS shows that the contact resistance of N,B-Ti₃C₂T_x-300oC is 0.52?.The capacitance retains 84%at a current density of 2 A/g after 1000 cycles.In the fourth chapter,N-doped MXene materials were prepared by high-temperature calcination with ammonia as the N source.Drawing on the fabrication process of paper chips in microfluidic technology,the planar microcapacitor structures with different shapes,sizes and electrode spacings on filter paper which were fabricated by ultraviolet lithography.The current collector and the electrode material were separately filtered on the patterned devices,and then the electrolyte was coated to construct nitrogen-doped MXene microsupercapacitors.The performance of the single and multiple devices connected in series and parallel as supercapacitors were investigated.CV and GCD electrochemical measurements of a single microsupercapacitor show that when the scanning rate is 5 m V/s and the current density is 1 m A/cm²,the volumetric capacitance is 41.89 F/cm³ and 41.07 F/cm³,respectively.The series/parallel CV and GCD performance tests of three interdigital microsupercapacitors show that nitrogen-doped MXene microsupercapacitors still have better stability and widening ability under the condition of increasing voltage,which can adapt to more electrical working environment,and expand its application fields;In the test of bending and long-term charge and discharge,good performance was maintained.After repeated bending for 100 times,the capacitance retention rate was 95%of the initial value.At the same time,after 10,000cycles of charging and discharging,the capacitance retention rate was 89%.It provides a theoretical basis from laboratory small batch production to industrial mass production.In the fifth chapter,a comprehensive summary of the whole paper,reviewing the problems solved by this work,and explaining the future development trend based on this work,finally,we also put forward a prospect for related work in the future.