Design And Electrochemical Properties Of MXene-based Composite Materials

With the increasingly prominent energy and environmental issues,the development of highly efficient and clean energy conversion and storage devices has become more and more important.As a new nanomaterial,two-dimensional material titanium carbide（MXene）has high specific surface area,high conductivity and thermal conductivity,and rich functional groups on its surface,which makes it have great value in energy conversion and storage devices.Therefore,the development of environmental friendly,simple and feasible MXene-based nanomaterials and improve the performance and application of MXene-based nanomaterials have become the focus of the world.In this paper,MXene-based nanomaterials were designed and synthesized.The electrochemical properties of the two materials were studied,and the mechanism of energy storage and electrocatalysis was discussed.The research content of the full text is divided into the following three parts:（1）Titanium titanium carbon（Ti₃Al C₂）powder was prepared by calcination at high temperature with titanium carbide powder（Ti C）,titanium powder and aluminum powder as raw materials.Then,HF and Li F/HCl were selected to etch Ti₃Al C₂ powder,and the composition,structure and morphology of the products were characterized.The results show that Ti₃Al C₂ phase materials are successfully synthesized by using the above materials.Under the same conditions,Li F/HCl etching method is more effective.The MXene prepared shows smooth plane and good layered stacking structure.（2）Herein,we have designed and synthesized a novel and highly conductive dodecaborate/MXene composites.The surface of MXene was modified by a simple ultrasonic treatment by adding of ammonium ion,and the dodecaborate ion was inserted into the inner surface of MXene by electrostatic adsorption.The results show that dodecaborate ion can act as a“lubricant”for ion diffusion between the MXene layers,which significantly improves the ion transfer rate of supercapacitors.The dodecaborate/MXene composites can achieve an extremely high capacitance of 366 F·g^-1 at a scan rate of 2 m V·s^-1,which is more than eight times higher than the capacitance of MXene(43 F·g^-1)at the same scan speed.After 5,000 charge/discharge cycles at a scan rate of 50 m V·s^-1,the capacitance retention rate of the material was 70.4%.This shows that the synthesized dodecaborate/MXene sample not only has excellent electrochemical performance but also has good cycle stability.（3）A novel Fe NC/MXene hybrid nanosheet was explored via pyrolysis of an iron-ligand complex and MXene nanosheets.The structure and morphology characterizations reveal that a thin and rugged Fe NC coating was closely attached on the surface of MXene,forming a hybrid nanosheet structure with an excellent conductive substrate and many electrocatalytic active sites on the substrate.The electrochemical measurements disclose that the Fe NC/MXene hybrid nanosheet exhibited a remarkable electrocatalytic performance,with a 25 m V higher half-wave potential（0.814 V vs RHE）than the Pt/C counterpart.More importantly,this hybrid presented a superb durability,with only 2.6%decay after a 20,000 s continuous test,much better than the 15.8%degradation for Pt/C.