Preparation And Electrochemical Characterization Of (cobalt, Ruthenium, Iron) Carbon Composites Based On Metal-organic Frameworks

With the rapid development of human society,environmental pollution and energy shortage have became two major problems.The search for new clean energy has become the direction of scientific research workers’efforts.Through unremitting efforts,more and more clean energy sources have been discovered,but because the research on new energy sources is not deep,and the problems of supply instability,intermittent and regional nature of these energy sources,they cannot be used well,and even cause serious waste of resources.Therefore,the research of energy storage technology and energy conversion technology of clean energy is the key to solve the problem of environmental pollution and energy.Hydrogen is a clean and renewable energy carrier,which has the advantages of high combustion calorific value,zero emission,environmental friendliness and so on.Water electrolysis is a method to produce hydrogen.Its theoretical decomposition voltage is 1.23 V,but in the experiment,because both cathode hydrogen evolution reaction（HER）and anode oxygen evolution reaction（OER）are involved in multi-step electron transfer process.The activation energy of multi-step superposition makes the actual voltage much larger than 1.23 V.How to design catalysts to promote electrocatalytic performance has become a research topic.At present,noble metal electrocatalysts are the best,which can greatly reduce the actual voltage in the catalytic process and greatly improve the oxygen evolution reaction（OER）efficiency.But actually,precious metal electrocatalysts are expensive and scarce,which makes them difficult to be used on a large scale.Metal-organic Frameworks（MOFs）is an organic-inorganic hybrid material formed by-assembly of metal ions and organic ligands under coordination bonds.MOFs have good stability and high porosity,large specific surface area increases conductivity and specific surface area adsorption properties,and MOFs materials are relatively cheap,which provides the possibility for the preparation of cheap high performance electrocatalysts.On this basis,the strategy of doping metal functional groups into MOFs channels is adopted to make MOFs have some properties of metal functional groups,and then carbonized to prepare the required electrocatalysts.After carbonization,the metal alloy formed in the hybrid changes in the electron orbit under the influence of carbon atoms.Due to the high electron transfer of bimetallic electrocatalysts and the synergistic effect of bimetallic atomic structures in conductive porous carbon frameworks,these bimetallic electrocatalysts promote the electrocatalysis of OER by providing low overpotential and good reversibility in alkaline electrolyte.In this paper,MOFs are used as a framework precursor,using the improved three-layer solution method:the metallocene（ferrocene,ruthenocene and cobaltocene）-doped organometallic complexes Fe（Ru,Co）-CoBDC were prepared by in situ diffusion reaction of terephthalic acid（H₂BDC）organic ligand solution with Co²⁺and metallocene（ferrocene,ruthenocene and cobaltocene）mixed solution in the interactive buffer layer.Then,the carbon-coated bimetallic alloy OER catalytic material Fe（Ru,Co）-Co@C was obtained by pyrolysis at high temperature.Microstructure was characterized by means of powder X ray diffraction（PXRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,X line photoelectron spectroscopy（XPS）and thermogravimetric analysis（TGA）.electrocatalysts were made from the obtained Fe（Ru,Co）-Co@C materials,and their electrochemical properties were deeply investigated by the Electrochemical Workstation.The main research contents are as follows:（1）Preparation and characterization of two-dimensional Fe（Ru,Co）-CoBDC organometallic compounds.The transition metal Fe,Ru,Cowas introduced into the MOFs frame by the improved three-layer solution preparation method.Ferrocene,Ruthenocene,Cobaltocene and Co²⁺were respectively added to the mixed solution of acetonitrile（CH₃CN）and N,N-dimethylformamide（DMF）as the upper reaction solution;Add H₂BDC to the mixed solution of CH₃CN and DMF as a lower solution;separating the two layers of solution with buffer layer of mixed solution of CH₃CN and DMF.The above three-layer solution was placed in a test tube,CoBDC,metal organic compound crystals synthesized by diffusion reaction of organic ligands and metal ions in buffer layer under constant temperature static state,at the same time,metallocene molecules were introduced in situ in its framework to obtain Fe（Ru,Co）-CoBDC complex.The results show that the synthesized CoBDC crystals exhibit two-dimensional nanosheet structure and metallocene molecules are successfully doped into the CoBDC framework.This in-situ reaction method provides a new idea for the preparation of MOFs-based two-dimensional composites.（2）Preparation and characterization of Fe（Ru,Co）-Co@C composites.The Fe（Ru,Co）-CoBDC composites were pyrolyzed at 600℃in nitrogen atmosphere to obtain carbon-coated bimetallic alloy Fe-Co@C,Co-Co@C and Ru-Co@C electrocatalyst materials respectively.The micro morphology,crystal structure,element analysis and electro chemical tests were performed respectively.In a three-electrode system,Linear Sweep Voltammetry（LSV）,Tafel curves,stability（i-t curves）and Electrochemical Impedance Spectroscopy（EIS）were measured in alkaline electrolyte（1 M KOH）.The results show that the bimetallic alloy electrocatalyst material has favourable OER activity,with overpotential of 320mV（Fe-Co@C）,335 mV（Co-Co@C）and 390 mV（Ru-Co@C）at current density of 10m Acm^-2,and has low Tafel slope,which indicates that it has fast catalytic reaction power,which is due to the two-dimensional structure with fast ion and electron transport channels.In addition,compared with the single metal catalyst Co@C,the bimetallic alloy catalyst formed by transition metal doping has higher OER activity.The mechanism of the synergistic effect between transition metals on the electrocatalysis performance was systematically studied.