Investigations Of Bimetallic Metal Organic Frameworks And Their Derivatives For High-performance Supercapacitors

Low energy density is the shackle of supercapacitors(SCs)to be solved.To meet the ever-creasing demand of energy,developing high-performance electrode material is the key step for enhancing the energy density of SCs.Metal organic frameworks(MOFs)with high specific area,high porosity and tunable composition/structures are the potential electrode material candidate for SCs.However,the conductivity of MOFs usually is inferior,which decelerates electron transfer and charge carrier diffusion leading to unsatisfying electrochemical properties.Herein,based on current situation,the main contents of this thesis are concluded as follows:1.Bimetallic Co Ni-MOF nano-array is synthesized through a mild solvethermal method and subsequent self-assembly.Compared with pure Ni-MOF-24,Co Ni-MOF nano-array shows higher electrochemical properties.The introduction of Co atom induces the lattice distortion of Ni-MOF-24,which shortens Co-Ni/Ni-Ni bond length and thus,increases the bond strength,leading to more stable structure.In addition,the high orientation of electrode material alleviates material stack,enhances the utility of electrode material and reduces the diffusion path of charge carriers.2.Vertically oriented Cu Ni-MOF array is successfully synthesized by using Cu(OH)₂ as the template and precursor.The effects of Cu doping on the conductivity and electrochemical activity of Ni-MOF-24 matrix are investigated theoretically and experimentally.The results show that the introduction of Cu atom changes the local electron distribution of Ni-MOF-24,and increases the density of electron states around the Fermi level,thus improving electrical conductivity.The Cu Ni-MOF electrode exhibits much higher electrochemical performance(the maximum capacity can reach 2103.33 F g^-1)than Cu(OH)₂ and Ni-MOF-24.Accordingly,Cu Ni-MOF//AC supercapacitor can provide a high energy density of 20.31 Wh kg^-1 at the power density of 850 W kg^-1.After 10000 cycles,90.5%of its initial capacity is remained.3.An integrated hollow,porous Cu Co-LDH electrode with hierarchical structure is successfully prepared by using Co-based MOF as the template and precursor.The doping effects of different atoms(Cu,Ni and Zn)in regulating the electronic structure of Co-LDH matrix is systematically analyzed via theoretical simulations.Compared with Ni and Zn doping,Cu-doped Co-LDH exhibits a lower energy gap,indicating that Cu dopant reduces the band gap and thus improves the conductivity of LDHs.In addition,the introduction of Cu distorts the crystal structure and induces dislocation defects.These dislocation defects produce dangling bonds on the electroactive surface and improve the activity of electrode materials.The maximum specific capacitance of Cu Co-LDH can reach 787 F g^-1,which is twice of pure Co-LDH.The corresponding Cu Co-LDH//AC supercapacitor can provide a high energy density of 22.15 Wh kg^-1.After 10000 cycle at the current density of 1 A g^-1,only 8.7%decay of energy retention is observed.