Unconventional Assisted Synthesis Of MOF-based Derivatives And Studies Of Their Electrochemical Properties

The rapid development of human society has led to the intensification of energy consumption.Therefore,finding new energy growth points and promoting the sustainable use of energy have become the consensus of major energy consuming countries in the world.There are a large number of renewable green energy sources in nature,such as solar energy,wind energy,tidal energy and water energy.It has become a hot topic for scientists to convert these renewable energy sources with strong discontinuities into sustainable and storable energy.Hydrogen production by electrolysis of water and lithium-ion batteries can turn the utilization of these energy sources into reality.Hydrogen has the characteristics of high energy density and clean combustion products.Compared with the hydrogen production method based on fossil resources,the electro-catalytic decomposition of water to produce hydrogen technology can convert intermittent renewable energy into hydrogen energy,which is one of the most potential green energy.As a supporting energy storage device,lithium-ion batteries have outstanding characteristics such as high energy density,high voltage,light weight,long cycle life and environmental friendliness,and have been widely used in various energy storage scenarios.In order to develop advanced energy conversion and storage technology,the performance of electrode materials is the first to be broken through.In recent years,the preparation of electrode materials based on metal organic framework materials（MOF）as the precursor system has attracted the attention of researchers.The advantages of metal organic framework materials lie in their ordered pore structure,large specific surface area and three-dimensional network structure.With its structural advantages,it can increase the contact area between the metal organic framework material derivatives and the electrolyte,which is conducive to the transfer and migration of electrons and ions.In order to further develop the advantages of the derivatives of metal organic framework materials,this paper explores the in-situ growth of metal organic framework materials on the collector,which can prevent the adhesive from covering the active sites and reduce the contact resistance between the catalyst and the collector.Microwave assisted synthesis and micro emulsion principle are to optimize the structure of metal organic framework materials from two directions of internal pore forming and particle size reduction,respectively.In this paper,using ZIF-67,MIL-88A and[NH₄][Co（HCOO）₃]as precursors,a series of derivates with controllable morphology and structure were obtained,and efficient electrolytic water catalysts and high-capacity anode materials for lithium-ion batteries were prepared.The specific research contents are as follows:1.Using MIL-88A as the intermediate control structure,two new-type iron phosphide/iron oxide electrocatalytic electrode systems based on Ni foam were prepared,and their overall electrocatalytic properties for water decomposition were preliminarily studied.Due to its high surface area and good conductivity,the adhesive free self-supporting Fe P-350/NF electrode exhibited excellent OER and HER performance.When the current density reached 10 m A cm^-2 in 1 M KOH electrolyte,the over potential was 154 and 122 m V,respectively.Using Fe P-350/NF as the negative and positive electrodes of the electrolytic cell,the electrolytic water current density of 10 m A cm^-2 is achieved at a voltage of 1.54 V,with good long cycle stability and better performance than most electrolytic water catalysts without adding precious metals.In addition,the study of Fe₂O₃/NF catalytic system further confirmed that the method of preparing electrolytic water catalyst with metal organic framework materials as the intermediate is universal.2.ZIF-67 was grown in situ on Ni foam by electrodeposition and solvothermal method based on the three-dimensional porous structure of Ni foam,and the synthesis of iron doped ZIF-67 was investigated.In situ grown Co P/NF and Co Fe P/NF on Ni foam were obtained by phosphating with Na H₂PO₂·H₂O.Due to its high surface area and good electrical conductivity,the adhesive free self-supporting Co Fe P/NF electrode exhibited excellent OER and HER performance.When the current density reached 50 m A cm^-2 in 1 M KOH electrolyte,the overpotential was 204 and 350 m V,respectively.Using Co Fe P/NF as the positive and negative electrodes of the electrolytic cell,the electrolytic water current density of 50 m A cm^-2 was achieved at a voltage of 1.81 V,with good long cycle stability.3.MIL-88A was prepared under the condition of microwave-assisted synthesis,and a series of novel structures with multiple cavities were obtainedα-Fe₂O₃ samples.The pore size in the prepared samples can be adjusted by the microwave irradiation time.Due to its unique cavity structure,Fe₂O₃-MW-4h nanoparticles have little structural change during rapid charge and discharge.The small size effect of Fe₂O₃-MW-4h nanoparticles makes it easier to fully contact the surface active sites with the electrolyte,so that the Fe₂O₃-MW-4h nanoparticles show greater lithium storage capacity.When the current density is 0.1 A g^-1,the capacity of Fe₂O₃-MW-4h shows an ultrahigh capacity of 955 m Ah g^-1.Even at a high rate of current density of 2 A g^-1,the capacity is still as high as 785 m Ah g^-1.In addition,the capacity of Fe₂O₃-MW-4h remains at 1010 m Ah g^-1 after 300 cycles under the high current density of 1 A g^-1,which indicates that the large capacity and long cycle of Fe₂O₃-MW-4h has very practical application prospects.4.Formic metal-organic framework material（MFF）was prepared by coprecipitation method as the precursor,and then calcined at 450 ^oC in air to obtain porous Co₃O₄ microspheres,which were used as anode materials for lithium-ion batteries because of their porous structure showed good capacity and excellent cycle stability.On this basis,the microemulsion method and bimetallic blending strategy were introduced into the synthesis of MFF,and the MFF precursor with a particle size of only 600 nm was successfully obtained.Zn Co₂O₄ was obtained by calcination of Zn Co₂O₄ as a precursor in air at 450 ^oC.Zn Co₂O₄ with nanometer size showed higher lithium storage capacity and excellent magnification performance at large current density,which is attributed to the fact that small size is more beneficial to the contact between electrode material and electrolyte,and the synergistic effect of bimetallic provides better electronic conductivity.