The Research On Preparation And Hydrogen Evolution Reaction Performance Of Nickel-based Compounds/MoS₂ Core-Shell Nanostructures

Hydrogen has characteristics of high calorific value,clean and renewable.Hydrogen is a very promising energy carrier.Among the hydrogen production technologies,electrocatalytic cracking of water has attracted much attention because of its characteristics of high purity products,no secondary pollution and abundance water resources.Catalysts are needed to reduce the dynamic overpotential of hydrogen evolution reaction in the process of electrolytic water.Noble metals such as Pt are the best catalysts to date.However,their scarcity and high price limit their large-scale applications.The development of non-noble metal electrolytic water catalysts with high catalytic efficiency and abundant earth reserves is the key issue to realize hydrogen as the main energy source.Among the non-noble catalysts,molybdenum sulfide has excellent theoretical catalytic activity.But its low conductivity and low density of catalytic active sites lead to far low actual catalytic performance compared with theoretical value.Both nickel-based selenides and sulfides have high electrical conductivity,chemical stability,high theoretical specific capacitance and high electrocatalytic activity.In order to further improve the catalytic performance of molybdenum sulfide.In this paper,nickel based nanostructures were fabricated hydrothermal method on nickel foam?Nickel foam?.And MoS₂ shell was further coated on the synthized nickel based compounds to obtain core shell nanostructures.The the composition,morphology and microstructure of the core shell nanostructures were studied.The electrocatalytic hydrogen evolution behavior was futher studied by electrochemical testing.The impacts of structure property on hydrogen evolution performance of the core shell sturctures were revealed.The main research contents and results are as follows:Nickel selenides with different composition and morphology were synthesized by two preparation methods by hydrothermal method.The impacts of reaction time,concentration of Se,and reaction temperature on the composition,morphology and microstructure characteristics of the product were studied.The influence of reaction conditions on HER were also stuided.The product synthized by Se powder/ethylenediamine method was three-dimensional dendritic Ni₃Se₂ nanostructure with polycrystalline rhombic crytstalline sturture.The trunk length of the nano-trees was about 5 um,and the branches average length of leaf-like nanostructures was about 140 nm.With the increase of growth time,the length of nano-trunks and branches changed a litlle,the diameter of branches increased.By using Se powder/NaBH₄ as precursors,the product was Ni₃Se₂/NiSe core-shell nanowires with monocrystalline rhombohedral Ni₃Se₂ as core,and hexagonal NiSe ultrathin nanosheets as shell.The coverage area of Ni₃Se₂/NiSe core-shell nanowires and the diameter of nanowires increased with the increase of Se concentration in precursors;with the increase of reaction temperature,the diameter of nanowires decreased.Both the three-dimensional dendritic structure and the core-shell structure can increase the specific surface area,and thereby help to increase the number of active sites and improve catalytic performance.Ni₃S₂/MoS₂ core-shell nanowires were synthesized by one-step hydrothermal method by using thioacetamide as sulfur source,sodium molybdate as molybdenum source and NF substrate as nickel source.The products have a network structure.The core was Ni₃S₂ with rhombohedral crystalline structure.The Ni₃S₂ core grow along[220]direction with a diameter about 100 nm.The MoS₂ shell is hexagonal phase with a diameter about 40 nm.Ni₃S₂ has good conductivity,which can effectively reduce the charge transfer resistance of core-shell structure.And a large number of sheet MoS₂ on nanowire surface could fully expose their edge active sites and improve HER performance.Ni₃Se₂/MoS₂ three-dimensional dendritic core shell nanostructures were synthesized by two step hydrothermal method.The surface of the NF substrate was sulfured to Ni₃S₂ by thioacetamide in precursors.1T-2H mixed MoS₂ nanosheets with single layer structure were prepared on the surface of Ni₃Se₂.Compared with 2H phase,the 1T-2H mixed MoS₂nanosheets have better conductivity and catalytic performance.N₂ adsorption and desorption tests show that core-shell nanostructures increase the specific surface area of the materials and can provide larger ECSA.Substrate NF and obtained Ni₃S₂ and Ni₃Se₂ have great conductivity,which could effectively reduce the charge transfer resistance of the catalysts.The core-shell structure showed great hydrogen evolution performance in electrochemical tests.In addition,because of the surface of NF was covered with a large number of stable Ni₃S₂,it could prevent the corrosion of acid electrolyte to the base NF to a certain extent.The catalyst also showed good stability under acidic conditions.