Preparation Of Iron-based Multi-shell Metal Compounds And Their Related Electrochemical Applications

The properties of materials depend not only on their chemical composition,but also on the internal structure of the material.Designing a special structure for the same material will give it good physical and chemical properties.Therefore,the construction of special structural materials is the focus of currently research.Due to its unique structural characteristics,multi-shelled hollow spherical materials exhibit many advantages,such as larger specific surface area,more active sites,better mechanical stress,higher conductivity,etc.,enabling them widely used in the fields of energy storage and electrocatalysis.Although researchers have explored a variety of methods for synthesizing multi-shell hollow structural materials,it is either not environmentally friendly or the process is cumbersome.Due to the limitations of the synthesis method,it is difficult to extend it to the synthesis of bimetallic or poly-metallic complexes.In this dissertation,iron-based metal compounds and complexes were selected as the research object.Urea was used as a coordination competitor with metal ions.One-step hydrothermal synthesis of carbon microspheres containing metal ions was used to obtain multi-shell hollow microspheres(MSHMs)after annealing,and hrough a series of test methods to study their application in electrochemical related aspects.The main work is divided into the following sections:1.Synthesis of metal ion carbon microsphere precursors by hydrothermal synthesis and annealing in air to obtain multi-shell hollow spherical ?-Fe2O3.Through the control of the reactants in the hydrothermal process,the formation mechanism of multi-shell hollow structure was explored.Annealed at three annealing temperatures,the results show that the ?-Fe2O3 microspheres annealed at 500? have the best performance.At a current density of 500 mA g-1,it can still maintain a high special capacity of 903.6 mA hg-1 after 1000 cycles.2.Design the multi-shell hollow spherical ?-Fe2O3 to be further phosphatized by high temperature,and successfully transform the multi-shell hollow spherical ?-Fe2O3 into multi-shell hollow spherical FeP2,and simply mix the FeP2 with the carbon nanotubes.The three-electrode system was used to test the electrocatalytic properties of hydrogen production in acid,alkali and neutral electrolytes.The results show that the Tafel slope is 55 mV dec-1 in 0.5 M H2SO4,64.9 mV dec-1 in 1 M KOH,and 163.2 mV dec-1 in 1 M Na2SO4.It shows an amazing stability.After 10,000 cycles of linear cycling,it still retains its original catalytic activity.3.Finally,in order to verify whether our synthesis method is suitable for the synthesis of bimetallic oxides,the other metal was introduced during the hydrothermal process.As a result,CoFe2O4 and SnFe2O5,which also with a multi-shell hollow spherical structure were obtained.Due to the doping of different atoms,the synergy between the metals is exerted.The initial discharge capacity reached 1330.75 mA h g-1,and maintain a high capacity of 701 mA h g-1 after 350 cycles at a current density of 500 mA g-1,achieving excellent lithium storage capacity.