Controllable Synthesis And Electrochemical Performance Optimization Of Two-dimensional Layered Carbide Material

Owing to the rapid consumption of fossil fuels such as coal and petroleum and the increasingly serious environmental pollution problems,the effective application of clean energy has become an important frontier research topic in the world today.Dye-sensitized solar cells（DSCs）and hydrogen production by electrolysis of water are effective ways to use solar energy and obtain hydrogen energy.Noble metal catalysts are used in both DSCs and the hydrogen evolution reaction（HER）involved in hydrogen production by electrolysis of water.However,the high cost and poor stability of precious metals have severely hindered their wide application in DSCs and HER.For this reason,the development of cheap,efficient and stable catalysts has important research significance.Transition metal carbides are recognized noble metal-like materials with high catalytic activity.However,the preparation of carbides generally requires a high-temperature carbonization process.On the one hand,energy consumption is very high,and on the other hand,the synthesized carbide particles are easy to agglomerate,which reduces the activity of the material.In response to the above scientific problems,this subject designed and synthesized a class of two-dimensional layered MXene carbide electrode materials.Firstly,the material with this special structure has high conductivity and catalytic performance;Secondly,the use of low-temperature etching to prepare MXene can avoid the high-temperature carbonization process,has low energy consumption,and is environmentally friendly.The specific research results are as follows:First,low-temperature etching was used to synthesize Ti₃C₂T_xand V₂CT_xwith two-dimensional layered structures,and the effect of etching time on the catalytic performance of this type of electrode in the DSCs system was explored.The study found that the Ti₃C₂T_xetched with 24 hours shows the highest activity,and the DSCs efficiency reached 6.2%while the V₂CT_xsynthesized by etching for 48 hours has the highest catalytic activity,and the battery efficiency reaches 6.14%.Due to the self-weight accumulation of the internal groups of the two-dimensional material and the agglomeration of surface groups,MXene cannot obtain the most ideal internal structure and surface composition.Although MXene exhibits a certain catalytic activity in the DSCs system,it still cannot be compared with the Pt electrode.To this end,this article further modified Ti₃C₂T_xand V₂CT_xby K⁺,Mg²⁺,and Li⁺intercalation to improve the activity.The experimental results show that the catalytic performance of the electrode is significantly improved by K⁺intercalation,and the device efficiency is increased to 7.11%（Ti₃C₂T_x）and 6.54%（V₂CT_x）,respectively.This is due to the increase of the layer spacing and the increase of catalytic active sites.However,the catalytic performance of Ti₃C₂T_xand V₂CT_xelectrodes decreased after Mg²⁺intercalation.This may be caused by the fact that Mg²⁺easily binds to the functional group F^-on the surface of MXene and adheres to the surface of MXene,reducing the surface catalytic active sites.The catalytic performance of the electrode decreased after Li⁺intercalation,which decreased to 3.11%（Ti₃C₂T_x）and 2.04%（V₂CT_x）,respectively.This may be due to the increase in the concentration of Li⁺in the electrolyte after Li⁺intercalation,which caused a decrease in device short-circuit current.In this paper,the synthesized MXene is further used in the field of electrocatalytic hydrogen evolution.By analyzing the current density of Ti₃C₂T_x,K⁺-Ti₃C₂T_x,V₂CT_x,and K⁺-V₂CT_xwhen the potential is at-0.5 V（vs.RHE）,it can be seen that the current density of K⁺-Ti₃C₂T_xand K⁺-V₂CT_xis higher than before intercalation.Increase from 0.2 mA·cm^-2,2.5 mA·cm^-2to 1.7 mA·cm^-2,7.5 mA·cm^-2,respectively.Because after K⁺intercalation,the interlayer spacing of the material becomes larger,which is more conducive to the diffusion of the electrolyte;at the same time,the electrode material after intercalation provides more active sites for the hydrogen evolution reaction.In summary,the two-dimensional layered materials of Ti₃C₂T_xand V₂CT_xhave been prepared in this work.They have shown certain catalytic activity in both DSCs and HER systems.The effect of ion intercalation on electrode activity is further investigated.The experimental results are useful for the development of low cost and high-efficiency noble metal-like electrode materials have certain reference significance.