Study On Controllable Synthesis And Structure-activity Relationship Of Doped Molybdenum Disulfide Based Electrocatalyst For Hydrogen Evolution

Hydrogen has been considered as one of the most ideal energy carrier in the future due to its high energy density,renewability and environmental friendliness.Water splitting into H₂and O₂ by electricity is expected to achieve large-scale clean hydrogen production of new routes,which can not only effectively avoid the high pollution and high energy consumption caused by hydrogen generation from reforming,but also make full use of power generation from renewable energy.While electricity driven hydrogen production from water splitting reaction needs electrocatalyst with high activity to lower the electrochemical overpotential,reduce production cost and improve production efficiency.So finding an efficient electrocatalyst is the key to the industrialization of hydrogen production by electrolysis of water.Pt-group metals show excellent performance for hydrogen evolution reaction（HER）in current,however,the high price and lower reserve limit their large-scale application in practical.Therefore,designing a cost-effective and high-efficiency electrocatalyst has attracted a lot of attentions recently.Molybdenum sulfide-based nanomaterials are always used as electrocatalysts due to their low cost,high efficiency and widely distribution.In addition,they are the most promising candidate to take the place of Pt-group metals.It is generally assumed that the real active sites of molybdenum sulfide locate on their edges.And the grapheme-like structure and semiconductor nature of molybdenum sulfide hinder the exposure of their active sites and result the lower transmission efficiency of electron,which restricts the further improvement of their electrocatalytic performance.Aiming at the issues of their two-dimensional structure and weak electrical conductivity,this dissertation uses three strategies to prepare molybdenum sulfide-based electrocatalysts with high efficiency for hydrogen evolution reaction:（1）enhanced their intrinsic activity through doping transition metal element;（2）exposed more active sites by designing typical nanostructure;（3）improved the electrical conductivity using carbon support.And we designed synthesis three kinds of molybdenum sulfide-based nanomaterials by combining two or three advantages of the aboved.The structure activity relationship between the microstructure and electrocatalytic activity of molybdenum sulfide was also discussed.In addition,the enhancement mechanism of their electrocatalytic performance have been analyzed.Thereby,this dissertation can provide the reference value for the designing and synthesis of a series of molybdenum sulfide-based electrocatalysts with excellent activity and low cost.Firstly,the synthesis and electrocatalytic performance of cobalt doped molybdenum sulfide on carbon support were investigated.The CoS₂/MoS₂/RGO ternary composite was synthesized by one-pot hydrothermal method.And the composition,morphology,size and electrocatalytic performance before and after the introduction into molybdenum sulfide-based nanomaterial were investigated.In addition,the effect of carbon support（such as RGO and CNTs）on the distribution of active component and the improvement of electrical conductivity were also been studied.Then the fundamental reason of the enhancement of electrocatalytic performance and the action mechanism of active phase were summarized.Then the molybdenum sulfide/carbon-doped molybdenum dioxide shell/core nanobelts were controlled synthesized using carbon-doped molybdenum dioxide as precursor through an in situ sulfurization process.The formation mechanism of the typical one-dimensional nanostructure and its effect on the electrocatalytic performance had been studied in detail.The result shows that compared with that of molybdenum sulfide nanoflowers formed by the accumulation of molybdenum sulfide nanoplates,the electrocatalytic performance of molybdenum sulfide/carbon-doped molybdenum dioxide shell/core nanobelts were enhanced obviously.The improvement of electrocatalytic activity is resulting from uniform distribution of molybdenum sulfide nanoplates and the vast exposed active sites,which is benefit from the in-situ sulfurization process and one-dimensional structure of molybdenum sulfide/carbon-doped molybdenum dioxide shell/core nanobelts.In addition,the remained carbon-doped molybdenum dioxide in the core area can contribute to the improvement of electrocatalytic performance of molybdenum sulfide/carbon-doped molybdenum dioxide shell/core nanobelts.CoMoS/CoMoO₄ shell/core nanorods were synthesized using CoMoO₄ nanorods as precursor.The effect of sulfurization time on the change of compositon and nanostructure of the product had been studied in detail.And the relationship between this change and the electrocatalytic performance of product have also been investigated.The results show that the moderate degree of sulfurization of CoMoO₄ nanorods precursor can either maintain the core-shell nanostructure or form vast active phase.In addition,the good electrical conductivity in the core area composited of oxide contribute to the improvement of electrochemical activity of the product.Based on the aboved experimental foundation,the CoMoS/CoMoO₄ shell/core nanorods assembled with nitrogen doped reduced graphene oxide,which integrates all above-mentioned merits including doping metal,designing low-dimensional nanostructure and conductive support,have been designed and synthesized.The results show that the as-prepared sample exhibit excellent electrocatalytic performance and stability.Thus,the method which can aggregate three merits provides significant guidance to the synthesis of molybdenum sulfide-based electrocatalysts.