Synthesis And Electrochemical Properties Of Transition Metal Sulfide/Selenide Electrode Materials For Supercapacitors Based On FeNi Prussian Blue Template

In recent years,with the rapid progress of economy and technology,energy crisis and environmental pollution have undoubtedly become serious problems facing the world.In order to solve these problems,people’s demand for exploring sustainable clean resources and energy storage equipment is increasing.With its relatively low cost,long cycle life and high power density,supercapacitors have become potential energy storage devices in electronic products and electric vehicle applications.The key factors for the recognition of these devices are their low cost,fast charge and discharge rate,high power density,life cycle stability and durability.Therefore,people have been committed to the development and exploration of supercapacitor electrode materials with excellent performance.As a class of metal organic framework compounds with adjustable chemical composition,Prussian blue analogs（PBAs）have become very promising materials for commercialization due to their high theoretical capacity,rigid framework structure and feasibility of mass production.However,some PBAs have poor electrochemical conductivity,so they cannot be directly used as electrode materials for supercapacitors.By converting PBAs into corresponding oxides,sulfides,selenides and phosphides,their electrochemistry conductivity can be greatly improved.In this project,Fe-Ni PBA nanocubes with an average size in the range of 100 to150 nanometers were obtained by co-precipitation of nickel chloride and potassium ferricyanide.Using Fe-Ni PBA as the precursor for selenization and sulfidation,（Fe,Ni）Se₂ and（Fe,Ni）S₂ electrode materials were successfully prepared.XRD,XPS,SEM,TEM and BET were used to characterize the crystal form,morphology and porosity of the material.The electrochemical performance of the material is tested by cyclic voltammetry（CV）,constant current charge and discharge（GCD）and alternating current impedance spectroscopy（EIS）.The main research contents and results are as follows:（1）The obtained Fe-Ni PBA material has an average size in the range of 100 to150 nanometers,showing a nanocube morphology.And at a current density of 1 A g^-1,the specific capacitance of the Fe-Ni PBA electrode is 443.1 F g^-1.（2）Through a simple and low-cost one-step hydrothermal selenization method,using hydrazine hydrate as a reducing agent,Fe-Ni PBA selenization process was used to synthesize（Fe,Ni）Se₂.Through the comparison of different experimental conditions,the best experimental conditions are obtained:the mass ratio of Fe-Ni PBA:Se powder is 1:1,the hydrothermal selenization temperature is 150℃,and the hydrothermal selenization time is 8 h.The electrode material has a specific capacitance of 796.85 F g^-1 at a current density of 1 A g^-1.In addition,after 5000 cycles of the electrode material at a current density of 10 A g^-1,its initial specific capacitance maintained 81.7%,indicating its excellent electrochemical cycle stability.Therefore,the excellent electrochemical performance of（Fe,Ni）Se₂ material proves that this material is a supercapacitor electrode material with certain market prospects.（3）Also through a simple one-step hydrothermal vulcanization method,with Na₂S as the vulcanizing agent,Fe-Ni PBA vulcanization treatment to synthesize（Fe,Ni）S₂.Through the comparison of different experimental conditions,the best experimental conditions are obtained:the concentration of Na₂S solution is 0.1 mol L^-1,the hydrothermal vulcanization temperature is 120℃,and the hydrothermal vulcanization time is 10 h.The electrode material exhibits a high specific capacitance of 1249.1 F g^-1at a current density of 1 A g^-1.And the electrode material has excellent rate performance and cycle stability.At a current density of 20 A g^-1,its specific capacitance remains at915.31 F g^-1.At a current density of 8 A g^-1,after 5000 cycles of charging and discharging,the initial specific capacitance maintained 91.6%.Afterwards,an asymmetric supercapacitor（ASC）composed of（Fe,Ni）S₂ and activated carbon（AC）has an energy density of 39.97 W h kg^-1 when the power density is 850 W kg^-1.Under the high power density of 8500 W kg^-1,its energy density still maintains a value as high as 20.95 W h kg^-1.The device also showed excellent cycle stability（retention rate of84.2%after 5000 cycles）.Therefore,this work provides an effective synthesis method for the preparation of high-performance electrode materials,and provides an important theoretical basis for the practical application of supercapacitors.