Synthesis And Electrochemical Studies Of MOF-derived Transition Metal (Co, Ni, Mn)@carbon Nanostructures

With the shortage of fossil energy in the world,we need to use energy conversion technology to solve this increasingly worrying problem.As a result,researchers around the world have been working on energy storage and conversion technologies,and these technologies have been developing rapidly.Electrocatalytic oxygen evolution(OER)is the core reaction of energy storage and conversion technologies such as fuel cell,metal-air cell and electrolytic water.The study of efficient electrocatalysts has become the core of the exploration of sustainable energy technologies.The performance of the electrocatalyst determines the energy consumption in the reaction process.The efficient electrocatalyst can improve the energy conversion efficiency of the oxygen evolution reaction,realize the efficient mass transfer and improve catalytic performance.Metal-organic framework complex(MOF)has a rich framework structure,adjustable pore size and stable structure.It has great potential in the preparation of carbon nanocomposite based on the nanostructure of MOF base material.In particular,bimetallic composites can be prepared by introducing metal complex particles into the MOF channel.This opens up a new way for the preparation of bimetallic electrocatalysts.In this study,the transition metal-doped two-dimensional carbon nanocomposite were synthesized by gas phase sublimation perfusion method and multi-layer solution diffusion method using the metal-organic framework complex as the substrate.By X-ray diffraction(XRD),scanning electron microscope(SEM),transmission electron microscope(TEM)and electron energy spectrum analysis(EDS),thermogravimetric analysis(TG),X-ray photoelectron spectroscopy(XPS),high resolution scanning electron microscope(HRTEM),inductively coupled plasma emission spectrum(ICP-and engage),N₂stripping absorption analysis method for the synthesis of carbon nanotubes composites microstructure characterization.The electrochemical performance of the prepared material was tested to study its electrocatalytic OER performance.The specific contents are as follows:1.Preparation and characterization of 2-D metal-organic framework complex Co-BDC.Two-dimensional Co-BDC nanosheets were prepared by improved multi-layer solution diffusion method.Co-BDC nanosheets were prepared by solution diffusion method in test tube using 1,4-terephthalic acid(C₈H₆O₄)as organic ligand,cobalt acetate(C₄H₆Co·4H₂O)as cobalt ion source,N,N-dimethylformamide(DMF)and acetonitrile(CH₃CN)as organic solvents.The crystal structure of Co-BDC was analyzed by XRD,and the morphology of Co-BDC nanosheets was observed by electron microscopy.2.Preparation and characterization of Nickelocene@Co-BDC nanosheets.The guest molecules of Nickelocene were introduced into the Co-BDC channel by gas phase sublimation perfusion to prepare nickelocene@Co-BDC composite structural materials.Spread the Co-BDC powder on the wire mesh(2000 mesh)and place it on the top of the agate pot.Nickelcene powder was placed in the bottom of agate pot and reacted in a vacuum drying oven at 100?for 72 h to obtain nickelocene@Co-BDC composite material.The crystal phase structure of nickelocene@Co-BDC was characterized by XRD.The nanocrystals showed regular and uniform two-dimensional lamellar structure with high aspect ratio by electron microscopy.3.Preparation and characterization of Ni-Co@carbon nanosheets.(1)The synthesized nickelocene@Co-BDC was directly and slowly pyrolyzed and carbonized in Ar atmosphere at 600?to form nano-sheets.(2)The microstructure of the nanosheet material prepared Ni-Co@carbon was characterized by XRD SEM,TEM,EDS,TG,XPS,HRTEM,ICP-OES and N₂adsorption and desorption analysis.The material was prepared into an electrocatalyst,and its electrocatalytic performance was studied by linear sweep voltammetry(LSV),cyclic voltammetry(CV),Tafel curve,electrochemical impedance spectroscopy(EIS),i-t curve and other electrochemical tests in a three-electrode system of electrochemical workstation.The results show that Ni-Co@carbon has a significant OER catalytic activity.In the 1.0 M KOH electrolyte,it only needs 243 m V overpotential to reach the current density of 10 m A cm^-2,and has a low Taefell slope(66.97 m V dec^-1)and good catalytic stability.The direct carbonization of the Co-BDC sample Co@carbon requires 310m V overpotential to obtain the same current density.Therefore,the doping of Ni leads to the decrease of OER reaction overpotential,which indicates that the introduction of Ni can improve the OER performance through doping effect.The influence mechanism of two-dimensional lamellar structure and multi-atom synergistic effect on OER performance was deeply analyzed.Density functional theory(DFT)was used to calculate the doping effect of Ni.4.Preparation and characterization of Mn-Co@carbon nanosheets.A 2-D layered Manganese@Co-BDC complex with manganese phthalocyanine as guest molecule was prepared by an improved four-layer solution diffusion method.The obtained Manganese@Co-BDC was directly and slowly carbonized at 700?under the atmosphere of Ar to obtain the Mn-Co@carbon core-shell type nanosheets.The microstructure of the material was characterized by XRD,SEM,XPS and ICP-OES.Through LSV,CV,Tafel,EIS and other electrochemical tests,the electrocatalytic performance of OER was studied.The results show that Mn-Co@carbon is a good non-noble metal electrocatalyst for oxygen evolution with low overpotential(291 m V)and Taefell slope(81.5m V dec^-1)in 1.0 M KOH electrolyte.The doping effect of Mn was studied.