Preparation And Properties Of CoFe₂O₄ Powders With High Specific Surface Area And Its Composites

Recently,with the gradually serious energy and electromagnetic pollution,people need to research the high-performance electrode materials and excellent microwave absorption materials using in the energy storage and microwave absorption.Therefore,the process and preparation of safe,low-cost,excellent properties of electrode materials and absorption materials have become a huge academic and technological challenge.Compared with simple oxides?Co₃O₄,Fe₃O₄?,CoFe₂O₄ gets much attention from the researchers,which can provide more reactive sites.The properties of CoFe₂O₄ depended on its structural characteristics,such as the micro-structural,size and stability.Therefore,it could improve the properties of the material that control of its structural characteristics.In this dissertation,a series of methods were used to design and fabricate CoFe₂O₄ with high specific surface area and its functional composites.The electrochemical properties of the electrode as a material for the supercapacitor and the microwave absorption properties as an absorber were studied.The specific things are as follows:?1?In this chapter,the effect of salt species on synthesis CoFe₂O₄ particles was investigated.The tested results show that the type of salt can change the shape,particle size and particle dispersion of CoFe₂O₄.When the type of salt added was NaCl,the dispersibility of CoFe₂O₄ particles are better.The specific capacitance of CoFe₂O₄ prepared with NaCl salt was 81 F g^-1 at a scan rate of 1mV s^-1.Co Fe₂O₄ maintains about 70.2%of its initial specific capacitance after4000 cycles.This study can be helpful to improv the electrochemical properties of CoFe₂O₄.?2?In order to improve the electrochemical properties of CoFe₂O₄,we adopt the chemical method to prepare the CoFe₂O₄ nanorods by increasing the specific surface area.The prepared CoFe₂O₄ exhibits a nanorods structure when the corroding time was 120 min.Then,the CoFe₂O₄ nanorods displays a high specific capacitance of 425 F g^-1 at a scan rate of 1 mV s^-1 and maintains about72.2%of its initial specific capacitance after 4000 cycles.The CoFe₂O₄nanorods own larger specific surface area compared with the Co Fe₂O₄ prepared by molten salt one.The larger specific surface area can offer more active sites,resulting in a significant increase in the electrochemical performance of CoFe₂O₄.This indicates that CoFe₂O₄ with a high specific surface area can be used as the electrode material for a promising supercapacitor.?3?A porous Ni-doped CoFe₂O₄ material was prepared by the impregnation method.Self-assembled polystyrene microspheres were used as templates,and the nitrate solution of metal ions was impregnated into the gaps of polystyrene microspheres.The porous Ni-doped CoFe₂O₄ material were prepared after sintering the polystyrene microspheres.The results show that the Ni atom is successfully and uniformly doped into CoFe₂O₄ and the porous structure of Ni-CoFe₂O₄ is prepared.When Ni doping amount is 0.5,the porous Ni-CoFe₂O₄ shows good electrochemical properties.The specific capacitance was 113 F g^-1 at a scan rate of 5 mV s^-1.The porous Ni_0.5Co_0.5 Fe₂O₄ electrode maintained about 108.3%of its initial specific capacitance after 4000 cycles.?4?In this chapter,the PANI-Co_0.5Ni_0.5Fe₂O₄ composite electrode was successfully prepared by an in situ polyanion reaction on the surface of porous Co_0.5Ni_0.5Fe₂O₄ with aniline monomers.The results of electrochemical tests show that the electrochemical properties of PANI-Co_0.5Ni_0.5Fe₂O₄ composite were greatly improved compared with single-phase materials in 1 M H₂SO₄aqueous electrolyte.When the scan rate was 2 mV s^-1,the specific capacitance of PANI-Co_0.5Ni_0.5Fe₂O₄ composites is 303.5 F g^-1,which is 60.7 times of the specific capacitance of the porous Co_0.5Ni_0.5Fe₂O₄ material and 1.9 times of the PANI electrode material.Thus,preparation of PANI-Co_0.5Ni_0.5Fe₂O₄ composite is an effective method for synthesizing high performance energy storage electrode.?5?As a traditional magnetic material,CoFe₂O₄ is also a conventional microwave absorption material.Thus,the microwave absorption properties of the CoFe₂O₄ before and after corroding 120 min were investigated.The maximum reflection loss?RL?for the corroded CoFe₂O₄ nanorods is-33.1 dB at 15.1 GHz.Moreover,the CoFe₂O₄ nanorods have a reflection loss value below-10 dB in the range of 12.1 to 13.0 GHz and 14.3 to 15.7 GHz when a matching thickness was larger than 2.5 mm.The CoFe₂O₄ nanorods are better than the CoFe₂O₄ for microwave absorption properties,which could be attributed to the larger specific surface area and better impedance match.