Design And Synthesis Of MoS₂-based Nanoelectrocatalysts And Its Application For Alkaline Hydrogen Evolution

With the dramatic increase in environmental pollution and energy crisis,humans are increasingly demanding clean renewable energy.As a highly efficient and clean renewable energy source,hydrogen attracts great attention from researchers.In industrial hydrogen production technology,Electrolysis water has the advantages of simple operation and environmental friendliness,which is considered to be one of mature and feasible technologies.However,at present,the best catalytic performance of Pt-based precious metal catalysts,but due to its rare,expensive restrictions on its widespread use.Therefore,there is an urgent need to develop an electrocatalytic hydrogen evolution catalyst that is highly efficient,inexpensive,and rich in raw materials.The activity of MoS₂ is close to that of Pt,and due to its low price and abundant resources,it has become a research hotspot in this field.However,MoS₂ is liable to be deposited and has poor conductivity,and there is still a large gap compared with the performance of the noble metal catalyst.The existing optimization methods include:size control,defect control,heteroatom doping,and material recombination to improve its electrocatalytic hydrogen evolution performance.However,the current research on the hydrogen evolution performance is mainly focused on the acidic environment,while the hydrogen evolution reaction under alkaline conditions is rarely studied.However,due to the fact that acidic solutions are prone to corrosion equipment that is not conducive to industrial production,the study of electrocatalysis under alkaline conditions is more conducive to the progress of industrial production.However,MoS₂ has low activity and poor stability under alkaline conditions.This paper starts with the characteristics and existing problems of MoS₂ and focuses on improving the hydrogen evolution performance of MoS₂-based electrocatalysts under alkaline conditions.The research was carried out mainly through the regulation of layer spacing,morphology,and electronic structure,and the selection of substrates suitable for use in alkaline environments.The morphology,structure,and composition of the materials were regulated by a simple hydrothermal method,and the optimized catalysts were also used.A comprehensive review of the performance was conducted to focus on the catalytic activity and stability of the hydrogen evolution of the catalyst in an alkaline environment,and to develop an appropriate hydrogen evolution electrocatalyst to lay the foundation for industrial applications.The main research content is as follows:1.The MoS₂ nanoflowers were synthesized by a simple hydrothermal method and uniformly grown on carbon cloth.The hydrogen evolution performance of MoS₂ under broad pH conditions was studied.By adjusting different loadings,the molar ratio of Mo:S is fixed and the optimal loading is selected.The results show that by using phosphomolybdic acid as the molybdenum source,prepared the MoS₂ with increase layer spacing,which improves the active site and conductivity.Compared with the sample obtained by physical mixing,it was found that chemical synthesis MoS₂ evenly grows on carbon cloth and the physical mixing results MoS₂ deposited on the carbon cloth.Moreover,electrocatalytic hydrogen evolution performance of the sample obtained by chemical growth is better than physical mixing.Among them,the optimal loading of nanomaterials exhibits higher hydrogen evolution activity under broad pH solution.The initial potential of the catalyst was only 94 mV under acidic conditions,the overpotential was 160 mV at a current density of 10 mA cm^-2,and the Tafel slope was 50 mV dec^-1.Under neutral conditions,the catalyst had a current density of 10 mA cm^-2 at the overpotential was 230 mV and the Tafel slope was 84 mV dec^-1.Under alkaline conditions,the catalyst had an overpotential of 188 mV at the current density of 10 mA cm^-2.And the Tafel slope was 52 mV dec^-1.Our results show that by combining with the carbon cloth substrate and increasing the interlayer spacing of MoS₂,it is beneficial to improve hydrogen evolution catalytic activity.2.Further,transition metal Co doping MoS₂ is used to improve its hydrogen evolution catalytic activity in alkaline environment.A series of cobalt-doped MoS₂nanosheets were synthesized by one-step hydrothermal method by adjusting the amount of Co added,and evenly grown on carbon cloth.Co-doped MoS₂(Co-Mo-S?1:3?/CC,Co-Mo-S?1:2?/CC,Co-Mo-S?1:1?obtained by adjusting ratio of Co:Mo.From the morphological observation,the molar ratio of Co to Mo is 1:2,and the deposition on the surface of the material is greatly reduced.The CoS₂ formed by doping with Co is interwoven with MoS₂.Due to the intrinsic hydrogen evolution property and good electrical conductivity of CoS₂,the hydrogen evolution performance is greatly improved after being compounded with MoS₂ under alkaline conditions.The starting point is only 34 mV.At a current density of 10 mA cm^-2,the overpotential is 91 mV and the Tafel slope is 82 mV dec^-1.It shows that Co doping MoS₂ through the highly active and conductive of CoS₂ and highly electrocatalytic active area of MoS₂ toward efficient HER.Through synergistic optimization,the Co-Mo-S/CC catalytic activity and stability for HER in alkaline environment are significantly improved.3.Next,by selecting inexpensive and abundant stainless steel?SS?as the conductive substrate to replace the expensive carbon cloth,through loading MoS₂catalyst to study the hydrogen evolution reaction performance in the alkaline environment.A series of MoS₂ nanoflowers were grown uniformly on SS by regulating different mesh stainless steel substrates.Compared with carbon cloth as the substrate,the results show that MoS₂ grown on stainless steel substrate in alkaline environment with excellent conductivity,good hydrogen evolution activity and durability.In the 1M KOH electrolyte,the optimized MoS₂/SS electrocatalyst at the current density is 10mA cm^-2,the overpotential reaches 160 mV,and the Tafel slope is low to 61 mV dec^-1.The results show that through the collaborative optimization of MoS₂/SS as a three-dimensional structure catalyst shows excellent electrocatalytic hydrogen evolution activity in strong alkaline environment.