Influence Of Interlayer Chemistry On The Preparation And Material Properties Of Two-dimensional Titanium Carbide

Two-dimensional titanium carbide（Ti₃C₂T_x,where T is surface functional group）was synthesized in 2011.Ti₃C₂T_x owns metallic conductivity and solution processability,which render it a promising material for conductive electrodes,electromagnetic interference shielding and electrochemical capacitors.This dissertation presents the understanding on the interlayer chemistry of Ti₃C₂T_x,the influence of interlayer chemical species on the material performance of Ti₃C₂T_x functional assemblies and the preparation of functional Ti₃C₂T_x material with special morphology.The main results are as follows:The material performances of Ti₃C₂T_x films,such as conductivity,mechanical properties and chemical stability,were proved to be greatly influenced by the intercalated chemical species.Extraneous intercalants（such as Li⁺）introduced during the preparation of Ti₃C₂T_x dispersion may exist in the resulting Ti₃C₂T_x films.Specifically,a protic acid exchange approach was proposed,which could remove adsorbed Li⁺from Ti₃C₂T_x nanosheets,resulting in the formation of pristine Ti₃C₂T_x films without extraneous intercalants.They display excellent conductivity(（1.04±0.02）×10⁴ S cm^-1),failure strength（102±11 MPa）and chemical stability（in H2O/O2 environment）;besides,pristine Ti₃C₂T_x films have good electromagnetic interference shielding performance(up to 5.16×10⁴ d B cm² g^-1 of absolute shielding effectiveness in the range of 8.2-12.4 GHz,for a3μm-thick film).Pristine Ti₃C₂T_x hydrogel with highly controllable microstructure was prepared.The existence of intercalated ions that promote hydration makes the Ti₃C₂T_x assemblies not stable in aqueous systems,henceforth the fabrication of Ti₃C₂T_x hydrogel matrix normally requires the addition of second components which may result in the performance deterioration.In this chapter,pristine Ti₃C₂T_x hydrogel with specific microstructure was prepared by thawing the frozen Ti₃C₂T_x dispersion in protic acids under specific conditions and a simple dialysis procedure.The microstructure of the hydrogel is controlled by the freezing process,namely,ice templates,and the thawing process was thoroughly understood based on the mass and heat transfer.Pristine Ti₃C₂T_x hydrogel with oriented microstructure displays good electrical conductivity(2.20±0.17 S cm^-1)at volume fraction as low as 1.2 vol%.The excellent photothermal properties of Ti₃C₂T_x as well as the vertically aligned pore structure in the hydrogel are beneficial to water evaporation applications,and the evaporation rate under 1 k W m^-2 is 1.9 kg m^-2 h^-1.Lightweight Ti₃C₂T_x powder material was prepared.Etching of aluminium layers in precursor MAX phase during the preparation of Ti₃C₂T_x is accompanied by the generation of H2 at interlayer space.Therefore,slowing the diffusion of H2 bubbles in highly viscous reaction media may lead to the formation of expanded Ti₃C₂T_x powder morphology.The resulted lightweight Ti₃C₂T_x powders have low apparent density(<50 mg cm^-3)and the processability characterized by normal powder materials.Static pressing the lightweight Ti₃C₂T_x powders at 300 MPa produces high-performance electrochemical capacitor electrodes which show large capacitance value(gravimetric capacitance of 272 F g^-1 and areal capacitance of 11.4 F cm^-2,1 m V s^-1)at mass loading as high as 42 mg cm^-2.The hierarchical pore structure at nanoscale and NH4⁺-intercalated structure are responsible for the observed performance,and the results may be illuminating to the fabrication of high-performance electrochemical capacitor electrodes.