Gas-Sensitive And Electrochemical Properties Of Two-Dimensional Mo₂CT_x MXene

MXene,a novel two-dimensional（2D）transition metal carbide/nitride material with large specific surface area and abundant surface functional groups,has important applications in electrochemical energy storage,catalysis,sensing and other fields.Mo₂CT_x MXene is a new member of the MXene family.Compared with the common Ti₃C₂T_x MXene,the properties of this material have not been well characterized.In this paper,the properties and applications of Mo₂CT_x MXene as room temperature gas sensitive material and lithium ion battery anode material are studied.In this thesis,Mo₂Ga₂C was prepared by a segmented high-temperature synthesis method.2D Mo₂CT_x MXene with graphene-like structure was synthesized with Mo₂Ga₂C as raw material and HF as etching solution.It was dissolved in Na OH solution for alkali modification,and the colloidal solution of Mo₂CT_x MXene was obtained by using tetrabutyl ammonium hydroxide（TBAOH）intercalation.The gas sensors,which are based on ceramic plate covered by Ag-Pd interdigital electrode,are assembled by coating colloidal solution of FL-Mo₂CT_x MXene/alkalized FL-Mo₂CT_x MXene on the surface of the substrate.Then its response to different gases at room temperature（298 K）was measured and compared.The gas sensor based on Mo₂CT_x MXene has a negative response to ammonia,triethylamine,and a positive response to formaldehyde.Mo₂CT_x MXene-based gas sensor has a short delay time for target gas and a fast response/recovery characteristic for ammonia gas,which is conducive to its rapid response in practical application environment.The sensor shows good repeatability with three responses to triethylamine and formaldehyde.In addition,the response of the sensor to triethylamine and formaldehyde shows a linear relationship with the gas concentration.After alkaline treatment,the increase of-O functional group at the end of Mo₂CT_x MXene surface not only changes the response type of Mo₂CT_x MXene to formaldehyde（from positive to negative）,but also effectively improves the room-temperature gas sensitivity of Mo₂CT_x based gas sensor.Compared with the response before alkalization,the response of Mo₂CT_x-based gas sensor to 500 ppm ammonia and formaldehyde was increased tens of times（average response was 24.4%and 17.4%,respectively）,and its response to triethylamine was increased 4 times（response value was 7.3%）.Alkalized Mo₂CT_x-based gas sensor shows the highest selectivity to NH₃.As a consequence,alkalized Mo₂CT_x has great potential in chemical sensors,especially in NH₃ sensors.In order to clarify the influence of alkali treatment on the electrochemical performance of Mo₂CT_x MXene,different lithium ion battery negative electrodes were prepared and tested.By comparing the first charge/discharge capacity,cycle stability and electrochemical impedance of the four samples,it is found that FL-Mo₂CT_x MXene has better long cycle stability and lower charge transfer resistance(R_ct)after circulation before alkalization.Alkali treatment can improve the gas sensitive performance of Mo₂CT_x MXene,but reduce its electrochemical performance as lithium ion battery electrode.