Synthesis And Electrochemical Performance Of Novel Mxenes-Ti₃C₂ Nanocomposites

In recent years,with the destruction of the environment and the reduction of fossil fuels,people urgently need to find green energy storage devices.Supercapacitors have become one of the indispensable energy storage devices due to their powerful power density and excellent cycle performance.Mxenes,a two-dimensional layered material,has excellent physical and chemical properties due to its special structure.As one of the most widely studied materials,Ti₃C₂ is a potential electrode material for supercapacitors.Due to the low specific capacity,easy stacking and oxidation of Ti₃C₂,In this work,Ti₃C₂ is compounded with transition metal sulfide?NiCo₂S₄?with different morphologies and conductive polymer?PANI?to solve the problems mentioned above.The work includes the following four aspects:?1?Ti₃C₂@PDA/NiCo₂S₄ that NiCo₂S₄ nanoparticles loading on the surface and interlayer of the Ti₃C₂ was prepared by hydrothermal method with Organ-like Ti₃C₂ as matrix material,NiCl₂·6H₂O as nickel raw and CoCl₂·6H₂O as the cobalt raw.In addition,it was applied to the supercapacitor electrode.The results showed that the specific capacitance of the Ti₃C₂@PDA/NiCo₂S₄composite is 495 F·g^-1 at scanning rate of 2 mV·s^-1,which increases the 10 times compared to the pure Ti₃C₂.Furthermore,after 3000 charge and discharge cycles,the specific capacitance retention of Ti₃C₂@PDA/NiCo₂S₄ is 81.16%.The main reasons of the performance improvement are the limited growth of NiCo₂S₄ and the synergistic effect between Ti₃C₂ and NiCo₂S₄.?2?In order to further improve the electrochemical properties of Ti₃C₂,the Ti₃C₂@PDA/NiCo₂S₄ nano-sheet composite was successfully prepared using mono-layer Ti₃C₂ as matrix,by two-step hydrothermal method,as well as analyze its mechanism of improving electrochemical properties.The results showed that the specific capacitance of Ti₃C₂@PDA/NiCo₂S₄ reached 1697.93F·g^-1 at scanning rate of 5 mV·s^-1,after 5000 cycles,the capacity can still reach76.67%,indicating that Ti₃C₂@PDA/NiCo₂S₄ nano-sheet composite material has excellent cycling stability.The excellent electrochemical properties of Ti₃C₂@PDA/NiCo₂S₄ can be summarized as follows:?a?as an excellent conductive matrix,Ti₃C₂ can prevent the agglomeration of NiCo₂S₄ and improve the conductivity of the composite material;?b?PDA can prevent the surface oxidation and structural damage in the process of hydrothermal synthesis of NiCo₂S₄,and can be used as a organic bridge between Ti₃C₂ and NiCo₂S₄ to make the contact closer;?c?NiCo₂S₄,as a kind of bimetallic oxide,can improve the specific capacity of the Ti₃C₂@PDA/NiCo₂S₄ composite by taking advantage of its high theoretical specific capacity.?3?In order to successfully prepare the Ti₃C₂@PDA/NiCo₂S₄ composite material that hollow tube NiCo₂S₄ supported on the surface of Ti₃C₂ using two-step hydrothermal method and the layer of Ti₃C₂ was used as the matrix,and cobalt hexahydrate and nickel hexahydrate were used as raw materials.The results of electrochemical test were analyzed and the conclusion was drawn that the Ti₃C₂ loaded with NiCo₂S₄ hollow tube can provide more additional electronic transport route to improve the efficiency of electronic transport.The specific capacity of Ti₃C₂@PDA/NiCo₂S₄ electrode reached 1927 F·g^-1 at 2mV·s^-1,which was significantly improved compared with Ti₃C₂ electrode.The capacitance retention of Ti₃C₂@PDA/NiCo₂S₄ electrode reached 67.57%after4000 cycles.?4?N-Ti₃C₂/PANI composite was prepared by electrochemical polymerization of Ti₃C₂ as carrier and it is applied to the supercapacitors.By electrochemical polymerization,polyaniline is uniformly loaded on interlayers and the surface of Ti₃C₂ Mxenes,which is conducive to preventing the dense stacking of Ti₃C₂ Mxenes,expanding the ion diffusion pathway and providing higher electrochemical activity.In addition,the combination of two materials with different energy storage mechanisms can improve the electrochemical properties of N-Ti₃C₂/PANI composites.When the electrochemical polymerization time was 420 s,the specific capacitance of N-Ti₃C₂/PANI reached 228 mF·cm^-2 at the scanning rate of 5 mV·s^-1,and the capacitance retention rate was 85%after 1000 cycles at the current density of 1 mA·cm^-2.