Preparation And Electrochemical Properties Of 3D Porous And 2D Porous MXenes

As a new two-dimensional material,MXenes have been widely used in many fields due to its excellent structure,especially in the field of supercapacitors.Although the electrochemical performance of MXene is better than that of many two-dimensional materials,it is susceptible to van der Waals forces and self-stacking,and it is prone to oxidation reaction under the action of air and water,which leads to the decline of electrochemical performance.Therefore,it is a new direction for the study of MXene to change the microstructure and obtain higher electrochemical performance through structural regulation.In this paper,the three-dimensional porous MXene structure was obtained by metal ion coagulation,and the MXene with two-dimensional channel structure was obtained by oxidation and etching.After that,the changes of the structure constitution were analyzed by various characterization instruments,and their relevance to the electrochemical performance changes was explored.The results show that,different metal ion coagulation overcomes the self-stacking problem of MXene,which produces a lot of irregular three-dimensional porous structures and forms a good conductive network.The interlayer spacing of the prepared nanosheets is increased significantly,which promotes the ion transfer and transport.The specific surface area and pore capacity are increased significantly,providing more active sites.After Mg²⁺coagulation treatment,the interlayer spacing of Ti₃C₂T_x-Mg reaches about1.433 nm,and the gravimetric specific capacitance of Ti₃C₂T_x-Mg is 420.50 F g^-1 in 3 M dilute H₂SO₄ electrolyte at the scanning rate of 2 m V s^-1,which is much higher than that of the original Ti₃C₂T_x.The three-dimensional porous conductive network effectively reduces the surface charge transfer resistance and ion diffusion resistance,significantly increases the contribution rate of the double-layer capacitance and improves the pseudo capacitance.The change of ion concentration will affect the pseudocapacitance.The Ti₃C₂T_x electrode obtained by oxidation and etching treatment not only successfully removes the oxidation products such as Ti O₂,but also improves structure and properties.After etching,the interlayer spacing of nanosheets is 1.457 nm,which is obviously larger than that of the original Ti₃C₂T_x.A large number of two-dimensional pore structures are produced on the surface of the nanosheets by etching,which provides convenient channels for ion transport.The electrochemical performance is also enhanced accordingly.The gravimetric specific capacitance is increased to 448.64F g^-1 in 3 M dilute H₂SO₄ electrolyte at the scanning rate of 2 m V s^-1.The surface charge transfer resistance and ion diffusion resistance are effectively reduced by the conductive network composed of two-dimensional channels,and the effect of pseudocapacitance is significantly enhanced.In addition,the increase of layer spacing improves the effect of surface capacitance,which also contributes to the improvement of electrochemical performance.