Construction And Properties Of Composite Electrode Based On Two-dimensional MXene

MXene,as a new type of two-dimensional materials,not only has the two-dimensional layered structure of graphene-like structure,high specific surface area and high electrical conductivity,but also demonstrates the advantages such as flexible composition and controllable thickness of the smallest nano-layer.As an electrode material,it has aroused much attention in the field of supercapacitor research.However,the self-stacking phenomenon between the MXene sheets leads to the reduction of charge transfer capability and hindering of ion diffusion,causing the lowered electrochemical utilization and the smaller capacitance performance.To solve the above problems,using Ti₃C₂T_x-MXene as the research object?MXene for short?,this paper has constructed MXene/polypyrrole,MXene/polyaniline and MXene/polypyrrole nanowire composite electrode materials by the direct electrochemical method and the electrostatic self-assembly method.Modern analytical testing techniques are used to systematically characterize it and focus on examination of capacitance performance.This research provides a reliable scientific basis and theoretical basis for the preparation and application of MXene in supercapacitor electrodes.The main contents of the full text are stated as follows:1.MXene/polypyrrole composite electrode materials were prepared by electrochemical co-deposition.In this process,the two-dimensional MXene nanosheets acted as core polymerization due to the functional groups on the surface of the two-dimensional MXene,and the pyrrole monomer radical cations?Py·+?was gradually polymerized on the surface of the two-dimensional MXene nanosheets,thus forming a composite electrode material with a three-dimensional carambola-like structure.First,Scanning electron microscope?SEM?,X-ray diffraction?XRD?,Fourier transform infrared spectroscopy?FT-IR?,and X-ray photoelectron spectroscopy?XPS?were used to characterize the surface and structure of the composite electrode material.Then,the electrochemical behavior of MXene/PPy composite electrode material was investigated.Benefiting from the vertical arrangement of MXene on the electrode surface,the occurrence of MXene self-accumulation phenomenon was fully avoided,and a high-speed charge/ion transfer channel was established to realize the construction of high-performance electrode material:the MXene/PPy composite film electrodes exhibited outstanding electrochemical performance with a high gravimetric capacitance of 416 F·g^–1 at current density of 0.5 A·g^–1 in three-electrode system.Moreover,the as-fabricated symmetric supercapacitors with MXene/PPy composite films coated ITO-glasses also exhibited a high specific capacitance(184 F·g^–1 at a scan rate of 10mV·s^–1),excellent reliability and good cycling stability(approximately 86.4%retention after 5000 cycles,at 5 A·g^–1).2.MXene/Polyaniline?PANI?composite electrode materials were prepared by cyclic voltammetry.In this process,the PANI monomer was induced and polymerized by the electric field and MXene surface functional group.One part of the PANI monomer was anchored on the surface of the electrode,and the other part was induced to polymerize between the two-dimensional MXene nanosheets.The synergistic effect of both realizes the construction of a three-dimensional structure of MXene and PANI on the electrode surface,is beneficial to high-speed charge transfer and rapid ion diffusion,and enhances the electrochemical performance of the electrode material.The surface analysis and structural characterization of the composites were carried out by means of SEM,XRD,FT-IR,Raman and XPS.MXene/PANI composite electrode material can reach the gravimetric capacitance of 417 F·g^–1 at a scan rate of 10 mV?s^–1 through an electrochemical test,retain 52%of the original specific capacitance value when the scan rate increases to 200 mV·s^–1,2.5 times?21%?of the pure PANI electrode,showing good rate performance.Finally,after 2000 times of cycling tests at current density of 1.0 A·g^–1,it has the capacitance retention rate of up to 83.4%,demonstrating a good application life.3.MXene/PPy-NW composite electrode material was successfully prepared by combining the Polypyrrole nanowires?PPy-NW?and the multilayered Ti₃C₂T_x-MXene through electrostatic self-assembly technology.The structure was characterized by SEM,XRD,FT-IR and XPS techniques,respectively.The characterization results showed that PPy-NW was used as intercalation agent to insert MXene between layers to expand its layer spacing and specific surface area.Finally,electrochemical tests show that the specific capacitance of the two-dimensional MXene/PPy-NW composite electrode material can reach 374 F·g^–1,when the scanning rate is 10 mV·s^–1,which is higher than that of pure PPy-NW(304 F·g^–1).When the scanning rate is increased to 200 mV·s^–1,72.4%of the initial specific capacitance can still be retained showing good multiplying performance.Finally,the capacitance can be maintained up to 91.6%after 2000 cycles experiments at current density of 5 A·g^–1,which has good cyclic stability.