Supercapacitive Performance Of CoFe Prussian Blue-Based Nanocomposite

With the depletion of fossil energy,energy security concerns and the rapid development of electric vehicles,it is indispensable to developing new energy storage technologies.Supercapacitors have attracted much attention in the study of new energy storage devices due to their high power density,fast charge/discharge and excellent cycle stability.However,the limited energy density of supercapacitors is the main challenge.Therefore,we focus on the preparation and electrochemical performance of nanostructerd CoFe Prussian blue?CoFePBA?and CoFePBA-based nanocomposites with the goal of improving the capacitance and rate performance of CoFePBA.More importantly,this research provides a new method to synthesize CoFePBA nanocomposites derived from cobalt-containing zeolite imidazolate skeleton structure material ZIF-67.In this dissertation,the core-shell structured CoFePBA@PANI and ZIF-67 derived CoFePBA-based nanocomposites are successfully synthesized.The detailed researches are as follows:1.A core-shell structure of CoFePBA@PANI nanocomposite is prepared by in situ polymerization of aniline?ANI?over the surface of CoFePBA nanocubes.In the preparation process,phytic acid?PA?is ultilized to coordinate with Co ions in CoFePBA nanocubes.The structural characterization and electrochemical performance tests of the CoFePBA@PANI nanocomposite are carried out.A specific capacitance of 401.2 F g^-11 is exhibited under the current density of 1 A g^-1 in 0.5 mol L^-1 Na₂SO₄ and H₂SO₄.When the current density increases to 10 A g^-1,the specific capacitance can still be maintained at 367.3 F g^-1.In addition,the reaction kinetics of the CoFePBA@PANI electrode is studied according to the equation i=a v^b?i is the current,v is the scan rate,a and b are variable parameters?,which further reveals the energy storage mechanism of the composite material.2.ZIF-67 material is used as a sacrificial template to prepare CoFePBA.Firstly,ZIF-67is synthesized via a simple coprecipitation reaction.Then,ZIF-67 is treated with[Fe?CN?₆]^3-or[Fe?CN?₆]^4-anions,which react with Co²⁺cations to form CoFePBA.The materials are characterized by FT-IR,XRD,XPS and SEM.Cyclic voltammetry,constant current charge discharge and the AC impedance method are used to investigate the electrochemical performance of the sample.A specific capacitance of 220.5 F g^-11 is exhibited under the current density of 1 A g^-1 in 0.5 mol L^-1 Na₂SO₄.When the current density increases to 10 A g^-1,the specific capacitance can still be maintained at 187.5 F g^-1.Furthermore,a hybrid supercapacitor CoFePBA//AC is assembled by using CoFePBA material as the positive electrode and activated carbon?AC?as the negative electrode,which can operate reversibly at a high cell voltage of 2.0 V with excellent cycling stability.A high energy density of 39.8 Wh kg^-1 is delivered at a power density of 797 Wh kg^-1.3.The MnO₂@CoFePBA nanocomposite is synthesized by a two step method,wherein MnO₂@ZIF-67 nanocomposite was first prepared and then converted into MnO₂@CoFePBA in the K₄[Fe?CN?₆]solution.Structural characterization and electrochemical performance tests of the nanocomposite were conducted systematically.The specific capacitance of MnO₂@CoFePBA is as high as 291.2 F g^-1 at a current density of 1 A g^-1.