Study On Preparation And Electrochemical Performance Of Two-Dimensional MXenes

Two-dimensional transition metal carbide,carbonitrides and（or）nitrides（collectively referred to as MXenes）was originally discovered and produced by Professor Gogotsi and his colleagues at Drexel University in the United States.MXenes is a layer structure and produced by the etching out of the A layers from the precursor MAX phase.So the general formula of MXenes is Mn+iXnTx,where M is the early transition element（mainly ⅢB～VIB Element）,X is C and（or）N,Tx represents surface functional group（such as-OH,-O and-F）,n=1,2 or 3.Due to its special structure and properties,MXenes has been extensively studied in the field of energy storage.Especially when used as a supercapacitor electrode,MXenes shows excellent capacitance.Because Mo2TiC2Tx has an ordered phase structure of double transition elements,it has broad application prospects in the application of MXenes supercapacitors.In this paper,we have studied about the electrochemical performance of d-Mo2TiC2Tx,the preparation process of its precursor Mo2TiAlC2 MAX phase and the etching,intercalating,layering process of d-Mo2TiC2Tx.Finally,the prepared d-Mo2TiC2Tx was tested for electrochemical performance such as mass specific capacitance,cycle performance and EIS test.All show that d-Mo2TiC2Tx has good electrochemical performance.Secondly,the sintering process of Mo2Ti2AlC3 and Ta4AlC3 two 413 types of MAX phases were studied,which laid the foundation for the next research.The specific research contents are as follows:（1）Mo2TiAlC2 sintering process:the mixed powder with the molar ratio of Mo:Ti:Al:C=2:1:1.2:2.After cold pressing,the powder has been kept in a vacuum atmosphere at 1450℃ for 1h.Then cooling down to RT in the furnace,a single Mo2TiAlC2 MAX phase was obtained.SEM microscopic morphology characterization shows that Mo2TiAlC2 has a typical layered ceramic morphology.（2）Preparation of d-Mo2TiC2Tx:Using 1g of Mo2TiAlC2 MAX phase powder into 20ml of HF acid solution and etching in a water bath at 50℃ for 60h,the multi-layer Mo2TiC2Tx t will be got.The XRD pattern shows that there is a small amount of Mo2TiAlC2 phase.The multi-layered Mo2TiC2Tx intercalates with TBAOH to obtain d-Mo2TiC2Tx powder obtained by suspending and filtering the suspension.SEM micro-morphology and TEM of the obtained d-Mo2TiC2Tx powder can prove the existence of a single layer or few layers.（3）Electrochemical performance test of d-Mo2TiC2Tx:The mass specific capacitance measured by cyclic voltammetry（CV）measured by the three-electrode test system at 2mV·s-1 and 5mV·s-1 is 62.21F·g-1 and 59.39F·g-1 respectively.The CV curve shows double layer characteristics.The constant current charge and discharge（GCD）have a mass specific capacitance of 34.44F·g-1 at a current density of 0.5A·g-1.The Nyquist diagram shows that dMo2TiC2Tx as an electrode material has a smaller equivalent series resistance and a larger active surface,and also has a good capacitance retention rate and stability in use.（4）Mo2Ti2AlC3 and Ta4AlC3 sintering process:Use the original molar ratio of Mo:Ti:Al:C=2:2:1.2:2.7 to configure the mixed powder.After holding at 1550℃ for 1h and cooling with the furnace temperature,a single Mo2Ti2AlC3 phase can be obtained;Use the original molar ratio of Ta:Al:C=2:1.2:1 to configure the mixed powder.After holding at 1400℃for 1h and cooling with the furnace temperature,a single Ta4AlC3 phase can be obtained.