Two-Dimensional Mxenes: Preparation And Applications In New Energy

Two-dimensional carbides/nitrides（MXenes）have rapidly developed over the last 10years,and have already been widely applied in various fields due to their excellent properties.Especially,MXenes have attracted tremendous attention in energy storage and biosensor.For example,ultrahigh energy density and large capacitance can be obtained in lithium batteries and supercapacitors by use of MXenes,and excellent sensitivity and fast response time have been demonstrated in sensor devices.Therefore,this thesis mainly carried out three research works about MXenes.1.Firstly,study of the effects of different intercalants on the structure and properties of MXenes were studied.The intercalation operation is performed after HCl/Li F etching,the intercalation with TBAOH,TMAOH,DMSO and ET,Ti₃C₂T_x MXene shows obvious difference in the structure and surface chemistry.Among all intercalated MXenes,TBAOH-MXene demonstrated the largest interlayer spacing of 16.58?,TMAOH-MXene,DMSO-MXene and ET-MXene interlayer spacing are 14.81?、14.19?and 13.92?,respectively.And the highest conductivity in all intercalated MXene belongs to DMSO-MXene with narrow interlayer spacing(2520 S cm^-1).In addition,the hydrophilicity TMAOH-MXene and TBAOH-MXene is better than that in DMSO-MXene and ET-MXene due to more surface groups of-O.2.Secondly,different intercalated MXenes were thus applied in supercapacitors,and the electrochemical performance was investigated based on different electrolytes of H₂SO₄and Na₂SO₄.Intercalated MXenes including TBAOH-MXene TMAOH-MXene,DMSO-MXene and ET-MXene were thus used as working electrodes in supercapacitors to understand the effect of interlayer structure and surface chemistry on their electrochemical properties.For H₂SO₄ as the electrolyte,TBAOH-MXene with the largest interlayer spacing shows the largest capacitance of 391.0 F g^-1,good rate performance and excellent cycling stability as well.While,for Na₂SO₄ as the electrolyte,all intercalated MXenes exhibit almost similar capacitance,indicating little impact of interlayer structure on the electrochemical properties.The largest capacitance(132.7 F g^-1)is found in DMSO-MXene among all intercalated MXenes,while TBAOH-MXene shows the smallest impedance and good rate performance.Furthermore,all intercalated MXenes exhibit perfect cycling stability with nearly 100%capacitance retention after 10,000 cycles.The results indicate that there is indeed a“saturated”interlayer spacing which can provide the maximum capacitance when the electrolyte ions are large,which means that the effect of interlayer spacing on the electrochemical properties will be limited when it reaches the“saturated”value.3.Finally,in order to fully utilize MXenes,A strategy of turning waste into treasure is proposed,the“residue”from the preparation of MXenes was recycled,and a flexible conducing film was fabricated by the combination of the different mass fraction“residue”（Ti₃C₂T_x-Ti₃Al C₂）and polyvinyl alcohol（PVA）.A Ti₃C₂T_x-Ti₃Al C₂/PVA film was prepared by composited with PVA,and the 25%wt Ti₃C₂T_x-Ti₃Al C₂/PVA film was uniformly distributed on the surface and had excellent electrical conductivity and mechanical strength.Using this films for sensing shows high sensitivity,with gauge factor up to 533 when the strain is less than 10%.Tests of human knuckle and wrist movement have also demonstrated that 25%Ti₃C₂T_x-Ti₃Al C₂/PVA has an extremely short corresponding time（<100 ms）.This research opens the way for the future reuse of waste generated in MXenes synthesis.