Design And Construction Of Structure-modulated MOF Electrode Materials With Superior Electronic Conductivity And Stability

Metal organic frameworks（MOFs）,with highly adjustable chemical components,flexible/long-range ordered topology and relatively convenient synthesis methods,have great potentials applied as supercapacitor（SCs）electrode materials.However,most MOFs are insulating and their metal-ligand coordination bonds are unstable in the electrolyte.It is these disadvantages that greatly limit the application of MOFs.The paper aims to maximize the application of the flexibility of MOFs through rational design.Under the premise of ensuring material stability,the conductivity of MOFs is gradually enhanced by means of structural modulation,and high-performance pristine MOFs and MOF-based composite electrode materials are prepared.The man research contents and conclusions in this dissertation were summarized as follows:1.Herein,a nanoscale MOF,Co_0.24Ni_0.76-bpa-200,possessing ultrahigh stability with uncommon semiconductor behavior(σ=4.2×10^-3 S m^-1)was fabricated by a combination of robust hydrophobic paddlewheel,optimized Co/Ni ratio,MOF size and conjugated degree of coligand.DFT study reveals that the appropriate Ni²⁺doping reduces the activation energy of system and thus yields a higher carrier concentration,and the strongly delocalized N-donor ligand notably increases the metal-ligand orbital overlap to achieve efficient charge migration,leading to continuous through-bond（-Co Ni-N-Co Ni-）_∞conduction paths.These structural features endow the Co_0.24Ni_0.76-bpa-200 electrode a very high specific capacity(1929.14 F g^-1)and good cycling stability（it could retain 86.5%of its initial capacity after10,000 cycles）.2.Based on the previous work,nitrogen-doped reduced graphene oxide（N-rGO）were in situ hybridized with Co_0.24Ni_0.76-bpa-200 to construct a nanoflower composite Co_0.24Ni_0.76-bpa-200@N-rGO with hierarchical pores and nanosheet-like"petals".The experimental and theoretical calculations show that the composite structure provides an efficient channel for electron transfer,and the overall energy storage mode is more inclined to the pseudocapacitive energy storage mechanism,which increases the specific capacity of the material to 2372.45 F g^-1.Meanwhile,due to the strong mechanical properties of graphene-like materials,the stability of the material is enhanced,it could maintain 91.2%of its original specific capacity after 10,000 cycles.