Preparation And Electrochemical Performance Of Ti₃C₂T_X Composite Materials

As a new two-dimensional material,MXenes have been reported in the field of energy storage and conversion because of their high surface area and excellent physical properties.Ti3C2TX is the most widely studied MXene by far.However,poor electrical conductivity and re-stacking between MXenes sheets severely hindered the maximization of its capacitance.In addition,the capacitance value of pure Ti3C2TX is limited.Therefore,composites based on Ti3C2TX with other materials are considered as an effective strategy to improve energy storage.Based on the above considerations,three Ti3C2TX composite materials were prepared in this paper,and their chemical properties has been investigated as electrode materials for supercapacitors.(1)A new supercapacitor electrode material Ti3C2TX@Al(T=OH,O)derived from Ti3AlC2 is prepared by partly removing aluminum using alkali etching method at 40 0C?By optimizing the alkali etching time,Ti3C2TX@Al-NaOH-36 with the best electrochemical performance and an increased specific surface area are obtained.In 1 M H2SO4,the material shows a high specific capacitance of 587 F g-1 at the current density of 1 A g-1,and 173 F g-1 at 10 A g-1.A low capacitance loss can be observed(0.0025%one cycle)after 6000 cycles test at the current density of 20 A g-1.This method circuments the use of F-containing reagent,and retains the aluminum layer reasonably,which inhibits the re-stacking of Ti3C2TX film layer.In addition,alkali etching roughened the surface of Ti3C2TX@Al,providing a larger specific surface area and more active sites,significantly improving the electrochemical properties of Ti3C2TX@Al-NaOH-36.(2)In order to solve the limitations of composite materials in last work,Ti3C2Tx@PEDOT composite materials were synthesized by multilayer Ti3C2TX and conductive polymer poly 3,4-ethylenedioxythiophene(PEDOT)by a simple in-situ polymerization method.PEDOT component effectively solves the problem of Ti3C2TX layer stacking and further improves the specific surface area of Ti3C2TX.Besides,PEDOT also provides additional pseudocapacitance.By optimizing the mass ratio between Ti3C2TX and PEDOT,the Ti3C2TX@PEDOT(1:10)electrode material with optimal electrochemical performance was obtained compared with the original Ti3C2TX material.The capacitance at a current density of 1 A g-1 was 564 F g-1,and the capacity retention after 10000 charge and discharge cycles was 96.5%.The enhanced capacitance and stability are due to the synergistic effects and surface redox process of the Ti3C2Tx@PEDOT.At the same time,the role of PEDOT as a support material avoids the accumulation of Ti3C2TX resulting in excellent cycle life.(3)With the rapid development of society,the development of flexible energy storage equipment is imperative.A new electrode material HHK-CC@Ti3C2Tx(HHK-CC=activated carbon cloth,TX=-F,=O or-OH)for flexible solid-state supercapacitor is prepared by a simple method.The activated carbon cloth(HHK-CC)is obtained by treating with potassium permanganate beforehand.A few layers Ti3C2TX flaks can be coated directly on the HHK-CC.When the loading Ti3C2TX on the HHK-CC@Ti3C2Tx electrode is 3 mg cm-2,the prepared electrode achieves a high capacitance of 1033 mF cm-2 at the current density of 1 mA cm-2.The specific area,oxygen-containing functional group,hydrophilicity and electrical conductivity of the activated carbon cloth increased significantly after the potassium permanganate treatment.When Ti3C2TX nanosheets were formed into the activated carbon cloth,the electrical conductivity,electron transport efficiency,and ion diffusion speed of the CC were improved,which significantly enhanced the electrical properties of the new material.After assembling to a symmetrical solid-state supercapacitor,the flexibility and mechanical strength of the carbon cloth are still reserved,and no significant capacitance decreasing under the conditions of bending and deformation.The capacitance value remains at 94.2%after 1000 cycles,and a high power density of 0.779 W cm-2 is obtained at the energy density of 4.5 ?Wh cm-2.