The Preparation Of Heterostructures Based Transition Metal Sulfides And Study On Their Energy Storage Performance

The demand for energy-storage devices and technologies is greatly increasing owing to the rapid economic development and increased demands of energy.Considerable efforts have been made to develop high power density conversion and storage system?e.g.,solar cells,supercapacitors and lithium ions batteries?.Among the multitudinous energy-storage devices,supercapacitors are primary choice for sustainable and renewable power sources because of their high power density,long cycle life,low cost,and environmental friendliness.Supercapacitors have been successfully utilized in many fields including communication,transportation,electronics,and aviation.Fundamentally,the performance of those systems directly relys on the properties of the electrode materials.Similar to graphene,the transition metal disulfides also possess layered structure,and the interlayer atoms are bonded by Van der Waals force,leading to the easily exfoliation and combine with other substances.In addition,transition metal sulfides have been considered to be a promising electrode material due to their rich redox sites and high theoretical capacitance.However,with its poor conductivity,the single component transition metal sulfides as an electrode material suffers from low energy density,and it's prone to re-stacking and aggregation,which would greatly reduce its predominant performances in practical applications.Heterostructures nanomaterials with different geometry and band arrangement can achieve effective electron hole separation due to their high quality heterogeneous interfaces,thus facilitating rapid charge transfer.Accordingly,the design and preparation of transition metal sulfides with ideal space structure and good conductivity will be an effective way to improve the properties of these materials.In this paper,different transition metal sulfide heterostructures nanomaterials were synthesized by a simple hydrothermal method,so a series of characterization and electrochemical performance tests were carried out.Major contents of our works include:?1?A simple one-step hydrothermal method for fabricating flower-like Bi₂S₃/MoS₂ heterostructures nanomaterials as electrode materials for high performance supercapacitors has been studied.In Bi₂S₃/MoS₂ heterostructure nanomaterials,and a superior heterostructure interface is formed.MoS₂ nanoparticles are closely connected to the surface of Bi₂S₃ nanorods,forming a superior heterogeneous interface,which is conducive to rapid electron conduction.In addition,the Bi₂S₃/MoS₂ heterostructure is used as the building unit,which is assembled into a three-dimensional flower-like nanostructure,providing an additional track for ion migration in the electrochemical process.As electrode materials for supercapacitors,the specific capacitance reaches3040 F g^-1at a current density of 1 A g^-1,and the capacitance remains at 1258 F g^-1when the current density is increased up to 30 A g^-1.The retained capacitance of the as-prepared flower-like Bi₂S₃/MoS₂ heterostructure is maintained up to 92.8%at 10 A g^-1after 5000 cycles,showing excellent cycling stability.Bi₂S₃/MoS₂ heteros-tructure electrode materials not only make full use of the excellent pseudo-capacitance behavior of Bi₂S₃ nanorods and MoS₂ nanospheres,but also produce synergistic effects between the two materials.Therefore,the prepared Bi₂S₃/MoS₂ heterostructure electrode material has higher capacitance and better rate performance.Reasonable heterostructure design between transition metal sulphides paves the way for high performance electrode materials and a new generation of electrical energy storage systems.?2?Three-dimensional flower-like MoS₂-CoSe₂ heterostructure nanomaterials were synthesized by a simple hydrothermal synthesis method.The in-situ growth of CoSe₂ nanocrystals can not only produce high quality heterogeneous interfaces,but also form three-dimensional porous structures,which enhances the electron conduction and avoids rearrangement and serious aggregation.Due to these unique structural characteristics,three-dimensional flower-like MoS₂-CoSe₂ heterostructure nanoma-terials exhibit excellent electrochemical properties.The results show that the specific capacitance of the MoS₂-CoSe₂ electrode materials is up to 1889 F g^-1when the current density is 1 A g^-11 and the capacitance can still be maintained to 896 F g^-1,when the current density increases to 20 A g^-1.In addition,when the current density is 20 A g^-1,the capacitance retention rate is 91.03%after 5000 cycles,which can maintain good cycle stability.When the power density is 800 W kg^-1,the water system symmetrical cell assembled with MoS₂-CoSe₂ as positive and negative electrode has a high voltage value of 1.6 V and a remarkable energy density of 60.1 W h kg^-1,which also shows good cyclic stability?the retention of capacitance is 83.62%after 2000 cycles?.?3?Different mass ratio of Ni?OH?₂-VS₂ heterostructure nanomaterials were successfully prepared by a simple hydrothermal method.Ni?OH?₂-VS₂ heterostructure nanomaterials exhibit better electrochemical properties than single component materials because of specific surface area,good electrical conductivity and the synergistic action between VS₂ and Ni?OH?₂ as electrode materials for supercapacitors.When the mass ratio of Ni?OH?₂ to VS₂ is 5:1,it has the highest specific capacitance of4021 F g^-1(at a current density of 1 A g^-1)and a long term cycling stability(80%capacitance retention after 500 cycles at a current density of 5 A g^-1).This method has good electrochemical performance and the material is cheap and easy to get good economic benefits.It can make Ni?OH?₂-VS₂ heterostructures become attractive electrode materials and have a broad application prospect in supercapacitors.?4?PANI/VS₂ heterostructures were synthesized by in-situ polymerization under acidic conditions and the effects of aniline content on their electrochemical properties were studied.After optimizing the conditions,we obtained that when the content of aniline was 2.76ml when the amount of VS₂ was fixed at 60 mg,the electrochemical properties of the prepared PANI/VS₂ heterojunction nanomaterials were the best.The composite structure of nanowires and nanochips in PANI/VS₂ provides a relatively short diffusion pathway to improve the utilization of active substances.We have studied its electrochemical properties and the results show that the specific capacitance is up to 2077 F g^-11 and have good cycling performance when the current density is 1 A g^-1.After 500 cycles,the specific capacitance retention rate is 96%when the current density is 51 A g^-1.It is a kind of electrode material with practical application prospect.