Preparation And Properties Of Hierarchical Porous Composite Electrode Materials Derived From MOFs Derivatives

As a promising energy storage device,supercapacitor has the advantages of fast charging rate,high power density,long service life and high safety.However,the low energy density has always been a major problem hindering its further development.For supercapacitors,the development of high-performance electrode materials from the perspective of phase composition and structure regulation is the key to solving the above problems.Among the many reported electrode materials,metal-organic frameworks（MOFs）have attracted extensive attention due to their porosity and highly controllable structure.Nevertheless,low conductivity has always been a problem that cannot be ignored.Based on this,the purpose of this thesis is to make full use of the advantages of MOFs,and to study the synthesis and electrochemical properties of MOFs derivatives.By combining ZIF-67 with carbon materials,combined with hierarchical structural design and high-valent element doping,the electrochemical properties of MOFs-related electrode materials are improved.The specific research contents are as follows:（1）CoP（CoP-NP@C）hierarchical porous structure supported by two-dimensional carbon skeleton was successfully prepared by simple carbonization and vapor phase phosphating using ZIF-67 directly grown on carbon cloth as precursor.Among them,CoP has high theoretical specific capacitance and good electrical conductivity,and the presence of two-dimensional carbon skeleton effectively promotes the full phosphating reaction.The specific capacitance of the prepared CoP-NP@C nanosheet electrode material is 540 F g^-1at 1 A g^-1,which is known to be a pseudocapacitive energy storage mechanism by combining calculation and analysis.The asymmetric supercapacitor composed of RGO has an energy density of 20.22 Wh kg^-1at a power density of 649.93 W kg^-1and exhibits good cycling stability,i.e.,92.4%capacitance retention after 10,000 charge/discharge cycles at a high current density of 10 A g^-1.It shows that the generated carbon skeleton effectively improves the conductivity and cycling stability of ZIFs.At the same time,the high specific surface area provided by the unique hierarchical porous structure promotes the electrochemical reaction of electrode materials.（2）The flower-like hierarchical structure of ultrathin sheet-like NiCo-LDH vertically inserted into a two-dimensional carbon skeleton was synthesized by one-step hydrothermal reaction using Co nanoparticles prepared by ZIF-67 after carbonization as nucleation sites.NiCo-LDH has a high specific capacitance due to its abundant redox active sites and large interlayer charge transfer distance.Using Co@C@NiCo-LDH as electrode material,the specific capacity is 881.4 C g^-1at 1 A g^-1.When the current density is 10 A g^-1,the specific capacity can still reach 773.1 C g^-1,and the retention rate is 87.7%,showing ultra-high rate performance.The asymmetric supercapacitor assembled with RGO has an energy density of 45.02 Wh kg^-1at a power density of 799.96 W kg^-1,and a capacitance retention rate of 77.8%after 10,000 cycles at a high current density of 10 A g^-1.Due to the reasonable construction of Co@C@NiCo-LDH hierarchical structure provides a high specific surface area and stable structure,providing more reactive sites,the electrode material exhibits excellent electrochemical performance.（3）Sodium molybdate（Na₂Mo O₄）was selected as the molybdenum source.By changing the doping concentration of Na₂Mo O₄,the crystal structure of Co@C@NiCo-LDH were regulated,and the effects of different Mo doping amounts on the electrochemical properties of electrode materials were analyzed.Mo doping introduced the existence of amorphous phase and effectively adjusted the electronic structure of NiCo-LDH,accelerated the charge storage kinetics,and limited the volume change of Mo-Co@C@NiCo-LDH.The specific capacity of 0.075Mo-Co@C@NiCo-LDH electrode material at 1 A g^-1is 1368.4 C g^-1,which is 1.56times that of 0 Mo doping,indicating that a reasonable Mo doping amount can further improve the electrochemical performance of the material.The asymmetric supercapacitor assembled with RGO has an energy density of 52.2 Wh kg^-1at a power density of 799.3 W kg^-1.Mo-Co@C@NiCo-LDH with large specific surface area exhibits excellent electrochemical performance due to its unique hierarchical nanoflower structure and doped optimized electronic structure configuration.