Electrochemical Properties Of Bimetallic Sulfides And Their Composites

Supercapacitors have attracted wide attention because of their high power density,fast charging and discharging speed,long cycle life,low cost and environmental friendliness,and have become one of the research hotspots in the field of new energy.However,the low energy density of supercapacitors is still an urgent problem to be solved.Therefore,increasing energy density without damaging its inherent advantages is the focus of further research.Because the performance of these devices is largely dependent on the electrode materials used,it is of great significance and challenge to develop advanced electrode materials with high capacitance,environmental protection and low cost.At present,the research on electrode materials focuses on improving the electrochemical properties of existing materials and developing new high-performance electrode materials.Metal sulfide is widely used as electrode material for supercapacitors because of its advantages of low price,abundant storage and environmental protection.Compared with single-component metal sulfides,bimetal sulfides and their complexes have richer REDOX reactions and higher electron transport rates,which have aroused extensive research interest in supercapacitors.In this paper,first of all,the preparation of a series of bimetallic transition metal sulfides,including cobalt nickel sulfide?NiCo₂S₄?,sulfide copper and cobalt?CuCo₂S₄?,zinc sulfide cobalt(Zn_0.76Co_0.24S),With this as the core,composite nanomaterials based on bimetallic transition metal sulfide were prepared,including NiCo₂S₄@MnO₂,NiMoS₄@NiS₂,and carries on the structural characterization and electrochemical performance testing.Main research contents include:?1?The porous NiCo₂S₄ nanometer material?NiCo₂S₄/NF?grown directly on nickel foam was successfully prepared and applied to supercapacitors.Such hierarchical nanostructure is constructed with interconnected ultrathin NiCo₂S₄ nanosheets subunits,forming numerous interspaces.The novel structure not only exposes more reaction active sites but also facilitates fast ion and electron transport.In addition,the integrated bind-free architecture ensures good conductivity.As a result,the as-fabricated NiCo₂S₄/NF exhibits a high specific capacity of 1209.7 C g^-1 at a current rate of 1 mA cm^-2,while maintaining an excellent rate capability and satisfactory cycling stability.The optimized device delivers a maximum energy density of 69.4 Wh kg^-1 at a power density of 372.1 W kg^-1.Moreover,energy density still retains a high value of 44.6 Wh kg^-1when power density reaches as high as 14.9 kW kg^-1.Meanwhile,an excellent cycling stability of 94.48%capacitance retention is obtained after 2000 cycles.?2?The CuCo₂S₄ nanotube cluster was synthesized and applied in the supercapacitor as a working electrode,the synthesized CuCo₂S₄ was a unique hollow nanotube structure,which can provide abundant active sites near the interface for rapid electrochemical reaction,so it has good electrochemical properties.The capacitance can reach 2643.6 C g^-1 when the current density is 2 mA cm^-2.the initial capacitance can be maintained at91.60%after 5000 cycles of charge and discharge tests at the current density of 10 mA cm^-2,reflecting good cycling performance.The reason is that its special structure can effectively avoid the collapse of the internal structure in the circulation process and ensure the stability of the whole structure.In a two-electrode system,the device also showed higher specific capacitance(174.5 C g^-1 at 0.5 mA cm^-2).?3?Zn_0.76Co_0.24S nanometer material was prepared.The electrochemical characterization results show that in the three-electrode system,it exhibits a high specific capacity of 2031.0 C g^-1 at the current rate of 1 mA cm^-2;when the current density is 30 mA cm^-2,the capacitance can still be maintained 888.9 C g^-1.At the current density of 10 mA cm^-2,the capacity retention rate can still be above 90.52%after 5000cycles,which proves good rate performance.In the asymmetric water two-electrode system,the capacitance is 166.5 C g^-1 at the current density of 0.5 mA cm^-2;the capacitance retention rate is 88.55%after 5000 cycles at the current density of 10 mA cm^-2,it has high specific capacitance and good electrochemical stability.?4?NiCo₂S₄@MnO₂ nanocomposites were synthesized successfully,the synthesized material has good electrochemical properties.In the three-electrode test system,the cyclic voltammetry scanning test curve of NiCo₂S₄@MnO₂ electrode material showed an obvious REDOX peak,indicating that the material was Faraday capacitor.The platform formed during the constant current charge and discharge process indicates that the REDOX reaction occurs during the charge storage process,which is consistent with the cyclic voltammetry test results.In the asymmetric two-electrode test,the cyclic voltammetry scanning test curve forms a large rectangle with no obvious distortion with the increase of sweep speed.In the process of constant current charge and discharge,the discharge time is long and the specific capacitance is large.When the current density is10 mV s^-1,the capacitance retention rate is up to 90.35%after 5000 cycles of cycle test,demonstrating good multiplier performance and cycle stability.?5?NiMoS₄@NiS₂ nanocomposite based on high performance asymmetric supercapacitor electrode material was successfully prepared.The microstructure of NiMoS₄@NiS₂ nanocomposite was characterized.NiMoS₄@NiS₂ nanocomposite had a flower-like structure,a disc-shaped core of NiMoS₄ and a thin petal of NiS₂nanocomposite.This special morphology can provide more active sites.In the three electrode system,the CV curve shows the REDOX peak,indicating that NiMoS₄@NiS₂nanocomposite has the characteristics of Faraday supercapacitor.The battery capacity is1348.0 C g^-1 when the current density is 1 mA cm^-2,and the battery capacity retention rate is up to 91.30%after 5000 cycles when the current density is 10 mA cm^-2.In the electrochemical performance test of two electrodes in an asymmetric water system,the specific capacitance of the device can reach 250.7 C g^-1 at the current density of 0.5 mA cm^-2,and its specific capacitance retention rate is 90.71%after 5000 cycles at the current density of 10 mA cm^-2,demonstrating its excellent cyclic stability.