Modification And Electrochemical Performance Of Two-dimensional Titanium Carbids Nanomaterials

Recently,two-dimensional transition metal carbides（MXenes）have already proved to be promising electrode materials for energy storage applications.Ti₃C₂ as one of this MXenes family members,has been extensively studied as promising electrode materials for supercapacitors.However,the multilayered Ti₃C₂ exhibits inferior specific capacitance due to its relatively low specific surface area and electronic conductivity.To solve above-mentioned problems,we conduct the following researches to further improve the electrochemical performance of Ti₃C₂.（1）Effect of the etching time on the synthesis of Ti₃C₂ was investigated.The results show that etching time can change the morphology,surface functional groups,and electrochemical properties of Ti₃C₂.And,Ti₃C₂ nanosheets with long etching time of 216 h（Ti₃C₂-216）exhibits higher specific capacitance of 118 F g-1 at the scan rate of 5 mV s-1,excellent rate performance,and cycling stability.This improvement in electrochemical performance is resulted from high carbon content for better conductivity and faster transportation of electrons,and the larger specific surface areas for more access of electrolyte to the electrodes.This study can be helpful in fabricating novel high-performance Ti₃C₂-based electrode materials.（2）To further improve the specific surface area of electrode material,Ti₃C₂ nanosheets decorated by TiO₂ nanoparticles（TiO₂-Ti₃C₂）were synthesized through a simple in situ hydrolysis and heat treatment process.The results indicate that TiO₂-Ti₃C₂ nanocomposites exhibit high specific capacitance of 143 F g-1 at 5 mV s-1 and excellent cycling stability.The introduction of TiO₂ nanoparticles can significantly enhance the electrochemical performance of Ti O₂-Ti₃C₂ by providing larger specific surface areas for more active sites,providing additional diffusion paths for electrolyte ions,and using as the interlayer spacing device preventing the collapse of the lamella,synergistically.It suggests that TiO₂-Ti₃C₂ is a promising electrode material for high-performance supercapacitors.（3）To increase the interlayer spacing and psedocapacitance of electrode material,the nanocomposites（MnO₂-Ti₃C₂）of Ti₃C₂ nanosheets modified by MnO₂ nanoparticles were synthesized through a simple liquid phase precipitation method and heat treatment process.The results show that MnO₂-Ti₃C₂ nanocomposites exhibit outstanding electrochemical properties of a high areal capacitances of 377 mF cm-2 at 5 mV s-1,high rate capability,and excellent cycling stability.The enhanced electrochemical performance mainly depends on the enlarged interlayer spacing for more intercalation of K+ ions,and conductive matrix for faster electrons diffusion.These results demonstrate that MnO₂-Ti₃C₂ nanocomposites offer fascinating potential for high-performance supercapacitors.（4）To further increase the conductivity and psedocapacitance of electrode material,nitrogen-doped Ti₃C₂（N-Ti₃C₂）nanosheets were produced by a facile one-step hydrothermal reaction using urea as nitrogen source.The results show that nitrogen is doped homogeneously into the N-Ti₃C₂ sheets matrix successfully.And,the N-Ti₃C₂ deliver a maximum specific capacitance of 156 F g-1 at a scan rate of 5 mV s-1,as well as an excellent rate capability and cycle stability.The main reason for the excellent electrochemical behavior of N-Ti₃C₂ is ascribed to the increased conductivity,the additional psedocapacitance provided by nitrogen-containing functional groups,and more intercalation of K+ cantion afforded by enlarged interplanar spacing,synergistically.It indicates that the N-Ti₃C₂ can be used as an electrode material for high-performance supercapacitors.