Preparation Of Flexible Freestanding Mxene-based Hybrid Films And Their Capacitive Performance

As a new generation of energy storage devices,supercapacitors have the advantages of high power density and long cycle life.Electrode material is an important part of supercapacitor,and its structure and performance directly determine the electrochemical performance of supercapacitor.Two-dimensional nanomaterials have potential research value in the fields of energy conversion and storage due to their atomic thickness and large specific surface area.Two-dimensional transition metal carbons and/or nitrides（MXenes）have become very promising electrode materials for supercapacitors due to their good hydrophilicity,electrical conductivity,tunable surface functional groups,and pseudocapacitive energy storage mechanism.However,the two-dimensional nanosheets tend to agglomerate under the action of van der Waals forces,which will limit the ion transport in the electrolyte and reduce the utilization of electrode materials.In order to solve the above problems,in this paper,the flexible freestanding MXene-based hybrid films with excellent electrochemical performance were prepared by embedding other conductive materials between few-layer MXene nanosheets and modifying surface functional groups,and further studied the assembled supercapacitor in portable electronics.The main research contents of this paper are as follows:（1）The concept of all-MXene hybrid film was proposed for the first time.The Ti₃C₂T_x/Nb₂CT_x hybrid films were prepared by vacuum filtration of few-layer Nb₂CT_x and Ti₃C₂T_x nanosheets,which effectively increased the self-stacking of MXene nanosheets and expanded the interlayer spacing of the same nanosheets.It’s beneficial to the rapid diffusion and transport of electrolyte ions in the hybrid electrodes.The fabricated all-solid-state supercapacitor can achieve an energy density of 5.5 mWhg^-1 and can be integrated as a stable power unit with flexible sensors for fabricating self-powered devices.（2）The large-area flexible freestanding Ti₃C₂T_x/V₂CT_x all-MXene hybrid films with controllable thickness were successfully fabricated by a simple one-step rolling process,which weakened the self-stacking of MXene nanosheets and constructed a highly interconnected conductive network.The gravimetric capacitance can reach 496 F g^-1 and has good rate capability.At the same time,it can also be used as a piezoresistive sensor material and integrated with the prepared all-solid-state supercapacitor as a self-supplied piezoresistive sensor,showing good piezoresistive performance.（3）The flexible freestanding Ti₃CNT_x films with ultra-high capacitance and rate capability were prepared by ion intercalation and vacuum annealing.After removal of the terminal group（-F/-OH）,more pseudocapacitance was created.At the same time,the intercalation of K⁺can expand the interlayer spacing.The prepared 300-KOH-Ti₃CNT_x film has a mass specific capacitance of 463.4 Fg^-1,which improves the utilization of electrode materials and further promotes the research of Ti₃CNT_xMXene in the field of supercapacitors.