Controllable Synthesis Of 2D/MOF Based Composites And Their Performance Of Supercapacitors

Two-dimensional(2D)materials,such as layered double hydroxide(LDH)and transition metal carbides,nitrides and carbonitrides(MXene),have shown great potential in energy storage.To obtain supercapacitors with high specific capacitance,fast charging-discharging and excellent cycling stability,the exploration of 2D materials such as LDH,MXene and their composites with MOF were studied in this thesis.The crystal phase and morphology of the samples were fully characterized,and the electrochemical properties were also studied.Based on the morphology,structure and electrochemical performance,the structure-activity relationship of the composites was analyzed to provide the basis for the design and preparation of high-performance electrochemical energy storage devices.The main research contents are as follows:1.The 2D ?-Co(OH)2/ZIF-67 composite was synthesized by one-pot coprecipitation method.The composition,morphology,and electrochemical property of ?-Co(OH)2/ZIF-67 were investigated.Furthermore,the ?-CoMn0.05(OH)x/ZIF-67 was synthesized using Co2+as primary metal source and Mn2+/Ni2+/Zn2+as the doping metal.The electrochemical test indicates that ?-CoMn0.05(OH)x/ZIF-67 exhibits the highest specific capacitance among the as-prepared composites,delivering a capacitance of 689 F g-1 at current density of 0.5 A g-1.An asymmetric supercapacitor based on ?-CoMn0.05(OH)x/ZIF-67 was fabricated,which can attain a high energy density of 70.5 Wh kg-1 at 13500 W kg-1.2.MOF particles(Cu-BTC,Fe,Co-PBA,ZIF-8,and ZIF-67)were fabricated on the surface of MXene via the adsorption of metal ions and in situ growing.The influence of synthesis conditions on MXene surface coverage and MOF morphology was investigated to achieve controllable synthesis.The composition and structure morphology of MXene/MOF composites(MXene/Cu-BTC,MXene/Fe,Co-PBA,MXene/ZIF-8 and MXene/ZIF-67)were investigated by structure characterization and electrochemical tests.Furthermore,ZIF-67 was converted into ZIF-67/CoV2O6 hollow structure via "ion-conversion-exchange".Electrochemical test results showed that MXene/ZIF-67/CoV2O6 exhibited higher specific capacitance than MXene/ZIF-67 and ZIF-67.The MXene/ZIF-67/CoV2O6//AC possess an excellent area energy density of 36.27 ?Wh cm-2 at 0.75 mW cm-2.As the power density increases,it can maintain at 30.63 ?Wh cm-2.3.Hierarchical MXene/ZIF-67/LDH composites were prepared via the etching of cubic ZIF-67 loading on MXene.Specifically,ZIF-67 core-shell(ZIF-67 CS),ZIF-67 yolk-shell(ZIF-67 YS),and Co,Co-LDH hollow structures were fabricated by adjusting the molar ratio of cobalt nitrate and ZIF-67 with ethanol and water as solvent.The composition,morphology,and electrochemical properties of the above materials were investigated by structure characterization and electrochemical test.The electrochemical performance is improved after compositing due to the synergistic effect of each component.In the three-electrode system,MXene/Co,Co-LDH exhibits the most excellent electrochemical performance with the specific capacity of 348.55 F g-1 at the current density of 1 A g-1.