Preparation And Electrochemical Properties Of Pseudocapacitance/Ti₃C₂T_x Composites

In recent years,supercapacitor,which combines the advantages of traditional capacitors and secondary batteries,has developed rapidly because of its potential application value in electric vehicles,electronic communications and other industries.For supercapacitors,the electrode material is the main factor in determining its performance,containing carbon-based materials?such as graphene,carbon nanotubes?,transition metal oxides?MnO2,TiO₂?and conductive polymers?PANI,Ppy?.To meet the requirement of high-performance supercapacitor,synthesis and electrochemical performance of composites for electrode has been extensively studied.In this work,the graphene-like two-dimensional layered Ti₃C₂T_x with large specific surface area and good conductivity were used to prepare electrode with MoO₃,TiO₂ and PANI.Firstly,MoO₃/Ti₃C₂T_x composites were prepared by precipitation-sintering method with ammonium molybdate and 2D layered Ti₃C₂T_x as raw materials.To study the effect of MoO₃ content on electrochemical properties,the composites with different MoO₃ contents were prepared.According to the results of X-ray Diffraction?XRD?,Scanning Electron Microscope?SEM?and Transmission Electron Microscope?TEM?,MoO₃ nanoparticles with size of about 40-70 nm are uniformly distributed on the surface,edge and interlayer of two-dimensional Ti₃C₂T_x,and the interlayer spacing of two-dimensional Ti₃C₂T_x increases,providing more active sites for ion attachment.The results of N2 adsorption and desorption show that the load of MoO₃ nanoparticles enhances the specific surface area of the electrode material.From the electrochemical performance tests,the cyclic voltammetry tests were carried out at a scan rate of 2 mV·s-1 in1 M KOH.The calculated largest capacity is 150.7 F·g-1.For cycling stability,the capacity retention is 93.7% after 8000 cycles.Secondly,depending on the oxidation of Ti₃C₂T_x,MoO₃/TiO₂/Ti₃C₂T_x composites were prepared by hydrothermal method through the hydrolysis of ammonium molybdate under acidic conditions.Active Ti atoms on the 2Dlayered Ti₃C₂T_x surface are connected with O,F,OH,both of which were replaced by hydrolyzate Mo?OH?x.Finally,the active Ti atoms and Mo?OH?x were oxidized into TiO₂ nanoparticels and MoO₃ nanoparticles under hydrothermal environment,respectively.According to the phase analysis and micro-structure results,we can clearly see that the large TiO₂ nanoparticles were distributed on the surface and edge of Ti₃C₂T_x,and the small MoO₃ nanoparticles were loaded between the layers.It can be seen from the electrochemical performance results that the largest specific capacitance of MoO₃/TiO₂/Ti₃C₂T_x composites was 142 F·g-1 at the scan rate of 2 mV·s-1 with electrolyte of 1M KOH.The capacity retention was 91% after 8000 cycles of charge and discharge.Finally,at the first stage,TiO₂/Ti₃C₂T_x composite was prepared by in-situ oxidation method.The size and crystal form of TiO₂ nanoparticles were controlled by adjusting the p H value,hydrothermal temperature and reaction time.Then,the hierarchical structure PANI@TiO₂/Ti₃C₂T_x ternary composites were obtained by combining polyaniline and TiO₂/Ti₃C₂T_x composites.According to the results of XRD,SEM and TEM,it is found that the TiO₂ nanoparticles produced in this experiment is anatase and distributed at the edges of Ti₃C₂T_x.The PANI nanosheets doped with HCl are grown on the surface,edge and interlayer of Ti₃C₂T_x and the size of the PANI nanosheets can reach tens of nanometers due to its orientation which reduces the limiting of layers space.From the results electrochemical performance tests,PANI@ TiO₂/Ti₃C₂T_x composites show the characteristics of the electric double layer capacitance in the electrochemical window of-1--0.3 V with 1M KOH as the electrolyte,and its gravimetric capacitance and areal capacitance are 188.3 F·g-1 and 435.4mF·cm-2.For the cycle life,the capacity retention is up to 94% after 8000 cycles.