Composition,Structure And Electrochemical Properties Of Nanocomposites Derived From Iron-Based Framework Complexes

Metal based complexes are the compounds with characteristic chemical structures formed by the complete or partial coordination bond of central metallic atoms or ions with the ligand molecμLes.They are widely applied in the field of energy conversion and storage because of their selective metal centers,various ligands,special structures and physical/chemical properties.Among them,iron-based framework complexes attract much attention due to the low price,environmental friendliness,high specific surface are a and porosity,in which the most widely investigated is iron based organic framework（MIL-Fe）and Prussian blue（PB）.The research about MIL-Fe and PB mainly focuses on the preparation of their derivatives and application to energy conversion and storage.This dissertation is focused on solving the problems existing in energy conversion and storage applications.The basic materials of MIL-Fe and PB are modified by introducing non-metallic/metal elements,conductive carbon materials etc.to prepare iron-based carbon nanocomposites through one-step heat treatment,and these iron-based carbon nanocomposites are applied to the electrochemical energy storage and catalysis.The main research resμLts include the following six aspects:1.Ferric chloride and dicarboxylic acid were used as sources to prepare MIL-Fe,which then was directly converted into carbon nanocomposites containing Fe ₃O₄（Fe₃O₄@C/PC）by one step high temperature carbonization i n N₂ atmosphere.The structure and morphologies of the sample were studied by SEM,TEM and other characterization methods,which shows that Fe₃O₄@C/PC is composed by the carbon coated Fe₃O₄ nanorods and porous carbon.The composite was used as anode material for lithium-ion batteries（LIBs）and the resμLts show that it has good electrochemical performance.At the current density of 0.1 A g^-1,the capacity still remains 1105.3mAh g^-1 after 150 cycles.Even at the high current density of 12 A g^-1,the discharge capacity can reach 309 mAh g^-1 after 2000 cycles.2.The three dimensional Prussian blue/reduced graphene oxide gel（3D PB/rGO）was synthesized through hydrothermal method using GO as carrier and PB as iron precursor.Then the 3D PB/rGO was transformed into 3D FeS₂-C/RG through one-step vμLcanization.The FeS₂-C/RG anode material in sodium ion batteries（SIBs）shows excellent electrochemical performance.Under the current density of 0.1,0.5 and 1Ag^-1,the specific capacity still remains 655.9,543.0 and 482.4 mAh g^-1 after 100cycles,respectively.The capacity of FeS₂-C/RG rapidly decreases from 672.9 mAh g^-1 to 337.4 mAh g^-1 within the first 300 cycles at the high current density of 6 Ag^-1,and the capacity attenuation of each cycle is only 0.0093%from 301 to 1000 cycles.3.The nitrogen phosphorus co-doped carbon coated ferrous phosphide nanomaterials（Fe₂P@NPC）with grid structure were obtained by one-step carbonizing the mixture of Prussian blue and phytic acid.Then Fe ₂P@NPC was used to modify the separator of lithium sulfur battery.Compared with the blank separator,the stability,rate performance and specific capacity of Li-S battery with Fe₂P@NPC separator are greatly improved.The electrochemical resμLts show that the capacity can still reach746.7 mAh g^-1 after 200 cycles at current density of 1 C,and the attenuation rate of each cycle is as low as 0.065%.Under the high current density of 2 C,the capacity still remains 422.3 mAh g^-1 after 600 cycles.The capacity still has 580.1 mAh g^-1 at the current density of 4 C,and it can reach 977.5 mAh g^-1 when the current density returns returns to 0.2 C,which demonstrates the Li-S battery with Fe₂P@NPC membrane has good reversibility and magnification performance.4.A series of precursors of cobalt iron Prussian blue（Co-PBs）were synthesized by substituting different amounts of cobalt for trivalent iron in Prussian blue.Then these precursors were carbonized under nitrogen atmosphere.The final carbon nanoderivatives containing Co and Fe were obtained（Co-Fe@NC）after acid pickling.The oxygen reduction reaction（ORR）performance of Co-PBs derivatives was tested and the electrochemical resμLts show that the Co-PBs derivatives with the molar ratio4.7:1 of trivalent iron to cobalt（Co-Fe@NC-1）has the best catalytic activity（Co-Fe@NC-1）.The Co-Fe@NC-1 displayed a positive initial potential of 1.043 V,excellent methanol tolerance and corrosion resistance,which are better than that of commercial Pt/C.5.The iron based framework complex（MIL-53）was synthesized by hydrothermal reaction using trivalent iron and terephthalic acid.Then the layered porous carbon coated iron,iron oxide and iron/iron oxide composites were respectively obtained through precisely controlling carbonization temperature of MIL-53.The SEM and XRD characterization methods show that with the increase of carbonization temperature,the iron oxides in the material are gradually reduced to low valence iron and finally transformed into single iron.The electrochemical properties of oxygen evolution reaction（OER）of MIL-53 derivatives under a series of temperatures were tested.The resμLts show that the OER performance of the composite obtained at900℃is the best.The overpotential is only 392 mV when the current density is 10mA cm^-2.The catalytic performance and stability of the composite are better than the traditional RuO₂ at high current density.6.The mixture precursor of Prussian blue,Ruthenium dioxide and polyaniline was converted into iron,Ruthenium and nitrogen co-doped hollow carbon nanoshell complex（Fe-Ru@HNC）by one-step pyrolysis.When Fe-Ru@HNC was used for hydrogen evolution（HER）in alkaline solution,its overpotential is only 18 mV,which is better than that of commercial Pt/C.The current density of Fe-Ru@HNC still remains 90.4%after 12 hours of long cycle,showing the excellent cycle stability.Th is nanocomposite with low load of Ru-Fe has the advantages of simple preparation process,low total cost and excellent performance,which provides the possibility for the practical application of platinμm-free catalyst for electrolyzing water in alkaline solution.