Functionalized MXene For Supercapacitors

As a new type of two-dimensional material,MXene has attracted much attention in various fields since its discovery in 2011.Its unique physical/chemical properties,excellent electrical conductivity,hydrophilic surface and high specific surface area are favored by supercapacitor researchers.The research about MXene-based supercapacitors is becoming more and more in-depth,but the general problem is exposed,which is that the MXene nanosheets are easy to stack and prone to oxidative degradation,leading to limiting the supercapacitor propeties.In view of this,this article attempt to suppress the occurrence of MXene stacking and oxidation.The research contents are as follows:A series of sandwich-like MXene based conjugated microporous polymer nanosheets(M-CMPs)were prepared by reacting p-iodophenyl modified MXene with conjugated microporous polymer(CMPs)monomers.The composite material not only inherits the high conductivity of MXene,but also has the high specific surface area of CMPs,which is beneficial to the performance of supercapacitors.In the case of M-PAQBz,a specific capacitance of 190 F/g was obtained,which is approximately twice the performance of PAQBz(106 F/g).More importantly,due to the covalent grafting of CMPs on the MXene surface,it plays a role in suppressing the stacking between adjacent MXene flakes.In addition,the surface modification of MXene reduced the active sites for the reaction of MXene with water and oxygen,and slowed down the oxidative degradation of MXene.The MXene/protonated thionine(MH/Th)hydrogel was prepared by electrostatic interaction.The protonated thionine solution is injected into the MXene dispersion.The thionine solution destroyed the electrostatic equilibrium of the MXene system and formed a three-dimensional hydrogel structure by layer self-assembly.The hydrogel structure suppresses the stacking of MXene nanosheets while retaining the hydrophilicity of MXene,which can greatly improve the accessibility of electrolyte ions.The amino functional group of the thionine molecule has a certain reducibility,which endows MXene with certain antioxidant properties.The oxygen-containing functional group of the thionine molecules can contribute to a certain pseudocapacitance and improve the performance of the material.Finally,MH/Th in the three-electrode system obtained a specific capacitance of 163 F/g,and the symmetric MH/Th cell device shows a specific capacitance of 79 F/g at a current density of 0.5 A/g.Furthermore,the device retains about 50% of the initial capacitance even though the current density is expanded by a factor of ten,exhibiting a good capacitance retention rate.In this thesis,MXene is optimized in terms of surface modification of MXene nanosheets,intercalation of conjugated microporous polymers,and assembly of threedimensional structures,in an attempt to suppress the occurrence of MXene stacking and oxidation,which provides a possibility for further promotion of MXene in the field of energy storage.