Study On A Novel Two-dimensional Material Of Mxene For Supercapacitors

Transition metal carbides and nitrides,known as MXenes,are an emerging class of 2D materials.The hydrophilicity of MXenes combined with their metallic conductivity,flexibility and surface redox reactions is the key to wide applications as the electrodes of supercapacitors.In this dissertation,we used Ti3AlC2 as the precursor to prepare 2D Ti3C2Tx(MXene)with lithium fluoride and hydrochloric acid by etching and exfoliation method.Because of the problems of easy stacking and easy oxidation at high potential of MXene nanosheets,a series of studies were carried out in this dissertation by means of intercalation and assembly matching into asymmetric supercapacitors.The main research results were as follows:1.The carbon nanotubes(CNTs)were intercalated into the MXene layers by liquid mixing,obtaining the MXene/CNT flexible electrodes.The effects of CNTs with different weight ratios(1%,5%and 10%)were investigated and a three-electrode configuration was used for the electrochemical performances test in 1 mol L-1 H2SO4 electrolyte.With the increase of CNTs,the rate performance of MXene/CNT was better than that of pure MXene,and the M/CNT-5%film exhibits high capacitance of 298 F g-1 at 1 A g-1 and good rate performance of 153.7 F g-1 at 1000 A g-1 with 51.3%retention.2.The AC/MXene flexible electrodes were obtained by liquid mixing,in which MXene could be used as a conductive binder.In addition,the effects of of ACs with different weight ratios(1:1,2:1 and 4:1)on the structure and properties of the flexible electrodes were investigated.With the increase of ACs,the distance between the MXene layers was enlarged and the specific surface area of AC/MXene was increased from 4.66 m2 g-1 of pure MXene to 2090 m2 g-1 of AC/MXene-4:1 film.Symmetric supercapacitors were assembled to test the electrochemical performance in 1 mol L-1 Et4NBF4/AN electrolyte,and the corresponding capacitance was increased from 17 F g-1 to 138 F g-1.The AC/MXene-2:1 film exhibited high capacitance of 126 F g-1 at 0.1 A g-1 and the best rate performance of 73.8 F g-1 at 100 A g-1 with 57.9%retention.3.Ruthenium oxide(RuO2)was prepared by the sol-gel method,and then combined with graphene to obtain ruthenium oxide/graphene flexible films.Using ruthenium oxide/graphene as positive electrode and MXene as negative electrode,the RuO2-G//MXene asymmetric supercapacitors were assembled,and the Swagelok tube fitting was used to investigate its electrochemical performance in 1 mol L-1 H2SO4 electrolyte.The electrochemical working window was 1.5 V,and the CV curve showed a capacitance of 62 F g-1 at a scan rate of 5 mV s-1.When the scan rate was increased to the 2000 mV s-1,the capacitance was 33 F g-1 with 53.2%retention.Furthermore,the asymmetric supercapacitors exhibited capacitance of 63 F g-1 at 1 Ag-1 and rate performance of 45 F g-1 at 50 A g-1 with 71.4%retention.Both tests showed that the RuO2-G//MXene asymmetric system had excellent rate performance.