Preparation And Electrochemical Performance Of Lamellar Nickel/molybdenum-based Composite Materials

The excessive use of non-renewable fossil energy has caused energy crisis and environmental pollution,and the development of new renewable energy and clean energy is imminent.Energy storage and conversion can be realized by using supercapacitor energy storage and electrocatalytic water decomposition to produce hydrogen.Due to their excellent electrochemical properties,transition metal compounds are widely used in supercapacitors and electrode materials for electrocatalytic hydrogen evolution reactions.Among them,nickel-based compounds have large theoretical specific capacity and considerable electrochemical reactivity,which can realize the needs of fast charging and discharging and high energy density of supercapacitors.Molybdenum based compounds are abundant in nature,with rich valence states and unique physical and chemical properties,which are not only used in supercapacitors for energy storage,but also for energy conversion of electrocatalytic hydrogen production.However,simple nicke/molybdenum-based materials such as nickel sulfide,nickel hydroxide,molybdenum disulfide and other nickel/molybdenum based compounds still have many shortcomings in terms of morphology,nanostructure and electrical conductivity,so it is necessary to design and synthesize nickel/molybdenum-based nanomaterials with different structures,and continuously optimize the electrochemical activity of electrode materials.The aim of this paper is to obtain electrode materials with high conductivity,specific capacity and electrochemical activity.A simple hydrothermal synthesis method is used to design multi-component composite and metal element doping methods to enhance electrochemical activity and electrical conductivity.The main research content of this thesis is as follows:1.Homogeneous MoS₂/PPy（MP）ultra-thin nanosheets（MP-rGO）were prepared on reduced graphene oxide（rGO）by multicomponent composite method.MoS₂ can be strongly coordinated with the N atom of PPy,allowing PPy to grow controllably on nanosheets,and enhancing the conductivity of MoS₂.As a substrate for MoS₂/PPy,rGO facilitates the dispersion of MoS₂/PPy and provides structural stability and charge transfer channels.In addition,the metal phase 1T-MoS₂ in the complex helps to increase the conductivity of the complex.Therefore,on the one hand,the ultra-thin nanosheet structure is conducive to the contact of the electrolyte and the stability of the structure,on the other hand,the synergistic effect of the three components enhances the supercapacitor performance of the material.The complex has A specific capacity of 1942 F g^-1 at 1 A g^-1 and can maintain a specific capacity of 635 F g^-1 at a current density of up to 20 A g^-1,indicating good capacity performance.In addition,after 3000 charge-discharge cycles,the specific capacity can still maintain 78.6%of the initial value.2.Multistage three-dimensional ZnS/ZnO/Ni（OH）₂ composites were in-situ grown on nickel foam by a multi-component composite method.The composites were composed of ZnS/ZnO/Ni（OH）₂ nanosheets and ZnS/ZnO nanospheres,during the synthesis process,ZnS promoted the formation of ZnO during the reaction and induced Ni（OH）₂ to form a unique three-dimensional multistage structure.The mesh composite material composed of nanosheets and nanospheres has abundant pores,which can increase the contact area between the electrode and the electrolyte and provide more active sites.Due to the unique structure and composition of ZnS/ZnO/Ni（OH）₂ composites,the specific capacitance at 1 A g^-1 and 20 A g^-1 is 1173.8 F g^-1 and 524.6 F g^-1,respectively,showing good magnification performance.3.The Ni_1-xMo_xS multilayer sheet nanostructures grown on the surface of nickel foam were prepared by Modoping method,and the effects of different hydrothermal reaction time and solvent ratio on the morphology of the composite were studied.In the reaction,the morphology and electronic structure of Ni₃S₂ are adjusted by Modoping,and the reaction kinetics and conductivity of Ni₃S₂ are improved.The nanosheet structure provides a large contact area of electrolyte ions,which is convenient for ion transport.The in-situ growth mode of Ni₃S₂ is conducive to reducing the electron transport resistance between layers,and has good electrochemical performance.The area specific capacity of the material is 4.3 F cm^-2 at the current density of 2 m A cm^-2,and can still maintain the specific capacity of 2.58 F cm^-2 at20 m A cm^-2.With Ni_1-xMo_xS composite and activated carbon as positive and negative electrodes,respectively,the assembled hybrid capacitor provides a high energy density of 60.5Wh kg^-1 at 494.7 W kg^-1.4.Mn S-MoS₂ bimetallic nanosheet composite（Mn S-MoS₂/LA-Mo）was in-situ grown on laser-treated molybdenum plate by multi-component composite method,and the phase,morphology and electrochemical properties of the prepared composite were analyzed.Here,molybdenum sheet is used as the substrate of the active substance,and after laser treatment,a micrometer-scale grid array is formed on the surface,which forms a super-hydrophilic interface and increases the electrochemically active area.Mn S-MoS₂ nanosheets with a thickness of only about 10 nm were prepared on this surface,and no stacking occurred between each other.Mn S-MoS₂/LA-Mocomposites have micron and nano scale heterogeneous structures,and the surface presents a large open space,which is conducive to electrode/electrolyte contact during electrochemical hydrogen evolution.At the same time,the synergistic interaction between MoS₂ and Mn S formed binary metal sulfide effectively increases the electrical conductivity and shows higher hydrogen evolution activity.Therefore,only a low overpotential（85 m V and 176 m V）is required for Mn S-MoS₂/LA-Moto reach 10m A cm^-2 in acidic and alkaline electrolytes,and there is no significant attenuation of the overpotential after 48 hours of durability testing.