Study On Preparation Of Two-Dimensional Layered Ti₃C₂T_x Material And Its Capacitance Properties

Transition metal carbides and carbonitrides, called Mxenes, have attracted widespread attention, since discovered. Mxenes are produced by selective etching of the A element from the MAX phases, which combine good metallic conductivity with hydrophilic. As a member of the MXenes family, Ti₃C₂T_x material not only have these features, but also its 2 D graphene-like layered structure, making it having potential application value and receiving considerable attention of researchers both at domestic and abroad in the energy storage field. In this paper, screening of the raw material Ti₃AlC₂, preparation, characterization and modification of Ti₃C₂T_x material are studied systematically and respectively. The physical properties and electrochemical performance of Ti₃C₂T_x material are comprehensively and deeply measured by X-ray diffraction（XRD）, scanning electron microscope（SEM）, nitrogen stripping absorption test（BET）, charge/ discharge measurements, cyclic voltammograms and other methods.Based on characterization of the raw material Ti₃AlC₂ microtopography and its structure, coupled with the electrochemical properties of its corresponding Ti₃C₂T_x, which is etched by the mass fraction of 40% solution of HF, the preliminary selections of Ti₃AlC₂ are Ti3-1 and Ti3-3 in order to meet the requirements of the experiments. The optimal preparation process of Ti₃C₂T_x material are explored further by controlling variable method, where the experimental variables are etching time and etching temperature. As the results, the optimum process conditions of raw material Ti3-1 are etching 6 h at room temperature, and Ti3-3 are etching 96 h under 60 ℃, respectively. The Ti₃C₂T_x materials produced in optimum conditions are measured in different concentration of KOH electrolyte and variours potassium electrolyte solutions containing 1 M K +,and the measurements consist of the CV curve, GCD curve and other electrochemical relevant tests.The experimental results show that Ti3C2Tx-3 material exhibits good electrochemical performance in 6 M KOH electrolyte solution and its quality specific capacity can reach 36.75 F/g, and Ti3C2Tx-1 material exhibits better electrochemical performance in 6 M KOH electrolyte solution and its specific capacity can reach 50.11 F/g. The capacity of Ti3C2Tx-1 material still remains 45 F/g after 1000 charge and discharge cycles, and the attenuation rate is 10.2%, showing good charging/ discharging cycling stability in 6 M KOH electrolyte solution. According to the experimental data, Ti3-1 is the best raw material and can meet the requirements of the experiments extremely.According to the characteristics of the Ti₃C₂T_x material, solution processing, alkaline treatment and annealing process are employed to improve the electrochemical performance of Ti₃C₂T_x material. The experimental results confirm that through XRD, SEM and the related electrochemical characterization, solution processing can change the structure of Ti₃C₂T_x and its electrochemical performance declines, so solution processing cannot improve the electrochemical properties of Ti₃C₂T_x material. Alkaline treatment can enlarge interlayer spacing and improve the electrochemical properties of Ti₃C₂T_x in some ways. In other words, alkaline treatment cannot improve the quality specific capacity but can improve the cycle stability of the material, and after 1000 charge and discharge cycles, the capacity has almost no degradation in 6 M KOH solution. Annealing process in the argon hydrogen mixture environment at various temperatures can effect the electrochemical properties of Ti₃C₂T_x material in different extent, with the increase of annealing process temperature from 250 ℃ to 400 ℃, and the electrochemical properties increase first and then sharply decrease. The specific capacity of the Ti₃C₂T_x material by annealing at 300 ℃ can reach 69.90 F/g in 6 M KOH electrolyte solution, increased by 39.5%, and the capacity attenuation is only 4% after 1000 charge and discharge cycles, and the annealed Ti₃C₂T_x material exhibts excellent capacitance properties.The characterization of XRD, SEM and BET show the annealed Ti₃C₂T_x material keep the original structure and enlarge the layer spacing, which is advantageous to the electrolyte ion diffusion and transmission.In brief, the raw material most meeting the requirements of the experiments most is Ti3-1 through selection from the three kinds of raw material of the Ti₃AlC₂. At room temperature, the experiments using the mass fraction of 40% solution of HF in 6 h has the best etching effect. Alkaline treatment can effectively improve the charging/ discharging cycling stability of the materials. In argon hydrogen mixture, annealing process at 300 ℃ can improve the material quality specific capacity and the cycle stability, which is an effective method to improve the material capacitance properties. Ti₃C₂T_x material shows exellent capacitive performance, and makes it being promising to apply in electrochemical capacitor as a new type of electrode material.