Study On Preparation And Performance Of Two-dimensional Titanium Carbide Mxene Based Composite

Ti₃C₂T_x,as a new type of two-dimensional material,is a material with great potential in many application fields due to its large specific surface area,high conductivity,low ion diffusion coefficient,excellent redox active surface,hydrophilicity,flexibility and adjustable surface chemistry and layered structure.The performance of Ti₃C₂T_x itself can be further improved by solving the problem of surface area reduction due to re-stacking caused by van der Waals forces.In this thesis,Ti₃C₂T_x two-dimensional materials were prepared.On this basis,composite materials of Ti₃C₂T_x/Mn O₂ and Ti₃C₂T_x/CNT were prepared respectively,and their applications as flexible electrode materials in supercapacitors were explored.In this thesis,Ti₃C₂T_x nanosheets were coated on the flexible carbon cloth substrate by pre-dipping,and then manganese dioxide nanosheets grew by hydrothermal method.The morphology and structure of the MXene/Mn O₂@CC flexible electrode were characterized and the electrochemical performance was tested.The optimal hydrothermal temperature is 120?,at which the loading of Mn O₂ is the largest and the adhesion of the composite material is stable,while the oxidation degree of MXene is not high.Manganese dioxide provides a pseudocapacitance much higher than MXene.The areal capacitance is 1781m F/cm².When the current density is 10 m A/cm²,the areal capacitance maintains66.3%of that at 1 m A/cm².Utilizing the high conductivity of Ti₃C₂T_x nanosheets enables rapid transfer of manganese dioxide Faraday charges and effectively reduces charge transfer resistance,which improves capacitance and rate performance,while its surface terminal functional groups can provide active sites for Mn O₂ crystals,which effectively increases active substance load.At a current density of 5 m A/cm²,it can still maintain a capacitance of 84.6%of initial capacitance after 5000 cycles.Ti₃C₂T_x reduces the volume change caused by the reversible adsorption/desorption process of ions into/from Mn O₂,which improves cycle stability.The electrochemical performance of the MXene/CNT@CC flexible electrode was studied.The areal capacitance of CNT/MXene@CC with 15%carbon nanotube mass fraction is 336 m F/cm²,which is 49.3%higher than the areal capacitance of MXene alone.When the current density is 10 m A/cm²,the areal capacitance maintains 76.8%of that at 1 m A/cm²,and the capacitance decays the slowest.The acidification treatment of carbon nanotubes introduces hydrophilic carboxyl groups and other functional groups to improve the hydrophilicity of carbon nanotubes,and then they could be mixed evenly with Ti₃C₂T_x nanosheets,which effectively inhibits the agglomeration of Ti₃C₂T_x nanosheets to increase the surface area,and provides a conductive path between Ti₃C₂T_x nanosheets to improve capacitance performance.When the mass fraction of carbon nanotubes is too high,the highly aggregated carbon nanotubes cause low porosity,which makes electrolyte infiltration and ion migration difficult.While the active material decreases,the active sites for redox reactions decrease,and the capacitance declines.When the load is increased from0.5 mg/cm² to 2.0 mg/cm²,the mass specific capacitance of the CNT/MXene@CC composite electrode attenuates by 26%from 247 F/g to 196 F/g,which is the smallest as the load increases.The presence of carbon nanotubes reduces the agglomeration of Ti₃C₂T_x nanosheets and maintains a better layered structure.Therefore,with the increase of Ti₃C₂T_x loading and the decrease of effective specific surface area,the decreasing trend of mass specific capacitance is slowed down.At a current density of 5 m A/cm²,it can still maintain a capacitance of 88.4%of initial capacitance after 5000 cycles.Carbon nanotubes maintain the separation of the Ti₃C₂T_x sheets during the charge and discharge process,which is beneficial to electrolyte ion diffusion and reduces sheets shedding to ensure excellent cycling stability.The widest stable potential window of MXene/Mn O₂@CC//CNT/MXene@CC flexible supercapacitor in double electrodes test is 1.8 V,and when the current density is 1 m A/cm²,the areal capacitance is 79.4 m F/cm².The performance of the capacitor is not significantly affected under different bending angles,so the flexibility is excellent.At a current density of 5 m A/cm²,it can still maintain a capacitance of 81.6%of initial capacitance after 5000 cycles.