Construction And Electrocatalytic Performance Study Of Metal-Organic Frameworks Composite/Derived Porous Materials

With the increasing demands for renewable energy and clean energy,the development of efficiently and stablely sustainable energy conversion devices has attracted scientists’extensive attention.Hydrogen production by electrolysis of water is a promising way to produce clean energy.However,due to the slow reaction of oxygen evolution in the water electrolysis device,the reaction rate of oxygen evolution in the cathode and the overall reaction of water electrolysis is severely restricted.Therefore,the preparation and synthesis of stable and efficient catalysts for oxygen evolution reaction is of great significance for the development of high-performance energy conversion devices.In recent years,the chemical transformation of functional materials such as inorganic materials and metal-organic framework materials has become an important way to fabricate porous nanostructures.Among them,MOF material derivatives inherit the porosity and abundant active sites of MOFs materials.Meanwhile,the flexible and controllable chemical composition and pore structure of MOFs materials make MOF derivatives show great application value in this field.In this thesis,we present a novel multi-step"molecular/ion exchange"synthesis method for the preparation of macro-/mesoporous Fe and Ni doped Co Se/Nitrogen doped carbon materials（MM-Fe,Ni-Co Se/NC）.Firstly,the cobalt based MOF material ZIF-67 nanoparticles were grown on the surface of the polystyrene（PS）nanospheres,and the core-shell structure of PS@ZIF-67 was obtained.Then PS@ZIF-67 was converted into a macro-/mesoporous cobalt coordination polymer（PS@MM-Co-CP）by means of molecule exchange,and further converted into PS@MM-Co-CP/Co-Fe Prussian blue analogs（PBA）/Co-Ni PBA（PS@MM-Co-CP/Co-Fe PBA/Co-Ni PBA）by the introduction of[Fe（CN）₆]^3-and[Ni（CN）₄]^2-ions.Finally,the PS@MM-Co-CP/Co-Fe PBA/Co-Ni PBA was prepared by heat treatment to MM-Fe,Ni-Co Se/NC nanoshells.Due to the presence of macro-/mesoporous pores and their diverse chemical composition,the material shows good catalytic performance of Oxygen Revolution Reaction（OER）.The current density of MM-Fe,Ni-Co Se/NC nanoshells with macro-/mesopores can reach 10 m A cm^-2 with overpotential of 285 m V,which is much less than that of the comparison samples with similar chemical composition but without macro-/mesopores,and the materials exhibit excellent stability in alkaline electrolyte.In addition to 0-dimensional PS nanospheres,this strategy can be further extended to more functional hard templates（such as 1-dimensional Mo O₃ nanowires and 2-dimensional GO nanosheets）to prepare and synthesize hierarchically porous nanoshells to obtain ideal functional composites.Similarly,we selected nickel foam as the hard template,soaked it in 2-methylimidazole and cobalt nitrate aqueous solution to prepare ZIF-67 sheet which is vertically grew on the surface of nickel foam.Two kinds of ions,[Fe（CN）₆]^3-and[Ni（CN）₄]^2-were introduced,and the MOF shell on the surface of nickel foam was etched into the uniform distribution of super-large porous ZIF-L/Co-Fe PBA/Co-Ni PBA/Ni foam.This material inherits the microporous structure of MOFs.At the same time,due to the arrangement of the lamellar MOF,there are large pores in the lamellar MOF layer and the existence of the etched super-large pore channels,which can allow the entry of macromolecules,reduce the mass transfer resistance and improve the mass transfer rate.At the same time,due to the good electrical conductivity of hard template nickel foam in this material,in order to explore the application of this material in the field of electrolysis water hydrogen and oxygen evolution,we studied the HER and OER bifunctional electrochemical properties of this material.