Study On Synthesis And Properties Of Ti₃C₂T_x Based Energy Storage Materials

In recent years,the two-dimensional?2D?transition metal carbon-nitrogen compound MXenes has been favored by researchers because of its unique and stable layered structure,electrochemical properties,and ease of preparation.The new MXenes family of materials consists of transition metal carbides,carbon nitrides and nitrides.M_n+1X_nT_x is used to represent the general formula of MXenes material.M in the formula is used to represent transition metals?such as Sc,Ti,Hf,Zr,V,Nb,Ta,Cr,Mo,etc.?,while x represents carbon or nitrogen,n is generally equal to 1,2 or 3,Tx is used to represent the functional groups on the surface of the material?-OH,-F,-O?.The name "MXene" is used to describe the similarity between this material and graphene.The excellent electrical conductivity,hydrophilicity,and high specific surface area of the MXenes material give it excellent electrochemical performance,and it has a great potential for application in electrode materials for supercapacitors.However,due to the effect of the surface functional groups of MXenes and its special layered structure,it leads to poor electrical conductivity between layers,less active sites,poor cycle stability,low specific capacitance,and needs further improvement.In order to further improveand optimize the electrochemical performance of MXenes,The Ti₃C₂-KOH-400,Fe@CNTs/Ti₃C₂T_x and TiO₂/C composites were prepared by ion-intercalation,microwave-assisted synthesis and rapid microwave oxidation using Ti₃C₂T_x obtained by etching Ti₃AlC₂ with HF.The results show that the MXenes material exhibits excellent electrochemical performance as a supercapacitor electrode material,especially in terms of cycle stability,specific surface area and specific capacitance.The specific research content is as follows:1.In order to increasing the electronically accessible surface area improves the electrochemical performance of Ti₃C₂T_x.First,the cation K⁺in the KOH solution is used for intercalation,followed by calcination to remove the surface and inter-layer functional groups?-F,-OH?of Ti₃C₂T_x,and increase the active sites in Ti₃C₂T_x.The results show that after the KOH and calcination modification,some of the end groups?-OH,-F?were removed,and the specific capacitance of the electrode material was greatly improved,which is 498 F g^-11 at a current density of 1 A g^-1,is almost nine times that of Ti₃C₂T_x,and retains over 97%of the capacitance after 3000 cycles of charge and discharge.2.Using Ti₃C₂T_x as precursor,ferrocene as raw material and carbon source,Fe@CNTs/Ti₃C₂T_x nanocomposites were rapidly synthesized by microwave assisted method.The raw material ferrocene is decomposed and converted to Fe@CNTs under microwave irradiation and grows directly on the layered Ti₃C₂T_x.Interlayer Fe@CNTs can effectively prevent the re-stacking of Ti₃C₂T_x flakes and increase the specific surface area of the composite(16.56 m² g^-1).In addition,the Fe@CNTs“bridge”between Ti₃C₂T_x flakes can provide fast electron transfer channels.Electrochemical performance tests showed that the specific capacity of Fe@CNTs/Ti₃C₂T_x nanocomposites reached 65.6 mAh g^-1,more than twice that of Ti₃C₂T_x electrodes.In addition,Fe@CNTs/Ti₃C₂T_x electrodes exhibit excellent cycling stability after 3000 cycles of charge and discharge.3.The Ti₃C₂T_x precursor was prepared by using Ti₃AlC₂ as raw material,and TiO₂/C nanocomposites were prepared by microwave oxidation.Microwave oxidation is a novel,simple and ultrafast method.The prepared TiO₂/C nanocomposite is a special layered structure of TiO₂ intercalated carbon layer.This structure not only increases the specific surface area(40 m²g^-1,the specific surface area of precursor Ti₃C₂T_x is 2.16 m² g^-1),and can increase the ion diffusion channel,improve the electron transport.The test results show that the TiO₂/C electrode material was used as the supercapacitor electrode material,and the specific capacitance remained unchanged after 5000 charge and discharge tests at a current density of 1 A g^-1.