Study On Preparation And Electrochemical Performance Of MXene Phase Ti₃C₂T_x

The MAX phase material is a family of layered ternary transition metal carbides or carbonitrides.Its two-dimensional structure has unique morphology compared with the three-dimensional structure,and thus brings interesting and novel characteristics.Currently,the only exfoliated non-oxide materials are graphene and boron nitride with the hexagonal van der Waals bond structure,and layered transition metal sulfides.After selectively extracting the"A"atomic layer in the MAX phase material structure,a two-dimensional layered separation structure MXene phase material can be obtained.This new material can maintain some of the characteristics of MAX phase materials,and has some excellent properties of graphene-like materials,such as high bending strength and elastic modulus,good electrical properties,high thermal stability,good electrical conductivity,hydrophilicity and stability in water environment.These excellent properties and unique structure make MXene phase materials with great potential in many applications such as energy storage,sensors and catalysts.In this study,high-purity Ti₃AlC₂ and Ti₃SiC₂ powders were macro-prepared by in-situ sintering,and their microstructure changes under different etching conditions were studied.Graphene-like two-dimensional Ti₃C₂T_x materials were macro-prepared and investigated.Its electrochemical performance was studied as supercapacitor electrode material.The main research contents are as follows:(1)By changing the ratio of raw materials and adding low-melting elements,high-purity Ti₃AlC₂ and Ti₃SiC₂ powders were obtained by pressureless sintering at 1400? and 1550? for 0.5 h.The phase formation laws of Ti₃AlC₂ in the sintering process at 1350-1550? and Ti₃SiC₂ at 1400-1650? were studied,and the macro synthesis mechanisms of Ti₃AlC₂ and Ti₃SiC₂ were studied.(2)Study on the growth mechanism of Ti₃AlC₂ crystal.The growing process of Ti₃AlC₂crystal conforms to the two-dimensional nucleation growth mechanism,including the two-dimensional nucleation of crystalline particles and the lateral expansion of the continuous growth layer.First,the crystalline particles are adsorbed on the smooth steps of the Ti₃AlC₂crystal(0001)basal surface to form two-dimensional hexagonal nucleus islands.As the molecules in solution continuously adhered to the interface,the side surface begins to grow continuously.At this time,on the basal surface of the new layer(0001),new crystalline particles will form new two-dimensional nucleus islands,which reciprocate to form the Ti₃AlC₂ crystal growth process.The superimposed growth process of the Ti₃AlC₂ crystal unit is that the Ti₆C octahedrons are first connected in a common edge and coplanar manner,instead of apex connection,and then Al atoms are connected with Ti-b to connect the Ti₆C octahedrons and form an Al atomic layer at the same time.(3)The structure changes of Ti₃AlC₂ and Ti₃SiC₂ under different etching conditions were studied,and it was found that NaOH hydrothermal etching has tendency to purify Ti₃AlC₂and Ti₃SiC₂.Compared with HCl+Li F,HF acid has higher efficiency and better layering effect,Which is more suitable for actual production.The MAX phase Ti₃AlC₂ and Ti₃SiC₂ are not as stable as Ti C under HF acid hydrothermal etching conditions and will be dissolved.Although the Ti₃SiC₂ layer is separated by the method of extremely cold liquid argon,the product after the treatment is not the expected phase Ti₃C₂T_x.(4)The Ti₃AlC₂ powder was chemically etched in the time range of 6-36 h by HF acid etching method,and the graphene-like two-dimensional Ti₃C₂T_x material was prepared macroscopically.The analysis of the products obtained under different etching times showed that shorter etching time makes the layer separation inconspicuous.Longer etching time will cause Ti₃C₂T_xflakes to fall off and overlap between layers.The etching time is 24 h to obtain uniform separation between layers and the layer spacing is 100-700 nm for MXene phase materials.Ti₃C₂T_x.The electrochemical analysis results show that the etched Ti₃C₂T_x has higher specific capacity than the raw material Ti₃AlC₂,and the specific capacity reaches144.29 F/g at current density of 0.2 A/g.The equivalent series resistance is reduced after etching,and the charge is transferred.The resistance is slightly increased,the diffusion resistance is reduced,the cyclic charge and discharge performance are better,and the specific capacity performance is improved,indicating that the Ti₃C₂T_x obtained by selective etching of the pure precursor has higher specific capacity.It shows that the HF acid etching method of massive preparation of Ti₃C₂T_x electrode material has great potential and can provide a theoretical basis for further production practice.(5)A few-layer Ti₃C₂T_x material was prepared by the hydrothermal auxiliary treatment method.During the hydrothermal treatment process,the reactor containing multi-layer of Ti₃C₂T_x material and alcohol are heated,so that under the action of high temperature and high pressure,the distance between the multi-layer Ti₃C₂T_x layers was obviously increased,or even separated.The thickness of the synthesized few-layer Ti₃C₂T_x can reach the nanometer level.Compared with the multi-layer Ti₃C₂T_x,the few-layer Ti₃C₂T_x can provide larger specific capacity,and the Cs can reach 292.86 F/g at a current density of 1 A/g.