Explore The Effects Of Metal Ions On MOF-Derived Materials For Supercapacitors

Due to high specific power density,fast recharge capability,long cycle life and environment-friendly feature,supercapacitors（SCs）have attracted a great deal of attention in the field of new energy sources.Metal-Origan Framewarks（MOFs）are new type of hybrid material assembled by inorganic metal ion and organic ligand.Their derived materials not only inherit characteristics of large specific surface area and porosity of precursors,but also can be controlled to synthesize some special structures of micro-/nanometers and hollow morphology,which have a wide application potential in supercapacitors.The preparation of MOF-derived materials is influenced by many factors,such as monrphologies,compositions and calcination conditions of precursors,controlling these factors skillfully help produce an ideal material purposefully.As the central node of the MOF,metal ion distributes uniformly throughout MOF,which undoubtedly plays an important role of MOF-derived materials.Therefore,this thesis focuses on the effects of metal ions on morphologies of MOF-derived materials and their electrochemical properties of supercapacitors.The main contents are as follows:1.In this work,a series of divalent metal ions have been used to react with phthalic acid（H₂pa）and 1,4-bis（imidazol-1-yl）benzene（bib）,which afforded MOFs 1-5 with the identical formula[M（pa）（bib）]_∞.They exhibit structural diversity because of different coordination modes of the metal ions,which indicates that the metal ion plays an essential role in the self-assembly of MOFs.Furthermore,five well-dispersed M_xS_y@C composites have been successfully synthesized through the one-pot sulfurization of MOF precursors,which prevents the sintered phenomenon in the stepwise carbonization-sulfurization process.Interestingly,the metal species originating from the precursors exert a crucial effect on the preparation of MOF-derived materials,which show obvious difference in morphology and electrochemical performance.Especially,NiS₂@C electrode exhibits outstanding specific capacitances because of its own electrochemical activity and helpful carbon graphitization,which is a potential electrode material.2.Six isomorphous MOFs 6-11 with 3D window-beam architecture have been synthesized from solvothermal reactions,which are mass collected and utilized as precursors to synthesize MOF-derived carbon with different morphologies.MOF-7 and 9lead to the derivation of porous carbons（PCs）,which exhibit remarkable BET specific surface areas;for derivates of MOF-6,10 and 11,graphitized carbons（GCs）show better conductivity,but their BET specific surface areas are relatively small;C-Cu prepared from MOF-8 has the smallest BET specific surface area,and there is no carbon graphitization.It is further confirmed that the metal ion of the parent MOF exerts a crucial effect on the preparation of MOF-derived materials,including the pore-forming effect of Zn and Cd species,and catalytic graphitization of Ni,Co,and Mn species.By studying the supercapacitance performance of MOF-derived carbon,their capacitances follow the sequence of PCs>GCs>C-Cu,which also reveals that the specific surface area plays a dominant role in the capacitive performance of electrical double layer capacitors（EDLCs）,and that the graphitization could improve the capacitance.