The Research On Preparation And Hydrogen Evolution Reaction Performance Of CoS₂ Nanostructures

Nowdays,the condition of insufficient energy and severe environment needs to be solved urgently.As a clean energy with environmental protection and high combustion heat value,hydrogen has attracted wide attention.Hydrogen production by electrolysis of water is widely studied due to its simple preparation method and no pollution.In the process of hydrogen production by electrolysis of water,it is necessary to use electrocatalyst to reduce the overpotential of hydrogen evolution,so as to achieve the purpose of efficient hydrogen production.At present,platinum and other precious metals are still the most efficient catalysts,but their high priced and limited amount of storage seriously restrict their global scale industrial application.Therefore,the development of low cost and high catalytic activity of non-noble metal electrocatalysts has important practical significance and research significance.In recent years,as a kind of low cost,Gibbs free energy(?G_H*)is close to thermal neutral and stable in acid and base media,CoS₂ has attracted wide attention of researchers.However,compared with the noble metal electrocatalyst,the comprehensive catalytic performance of CoS₂ still needs to be further improved.In this thesis,316 L stainless steel fiber mat(SSF)with excellent electrical conductivity,large specific surface area and super good stability was used as the substrate.CoS₂ nanostructures with different compositions,morphology and microstructure were synthesized by different methods.The influence mechanism of morphology,microstructure and heteroatomic doping on the catalytic performance of CoS₂ electrocatalyst was studied.Specific research contents and results are as follows:Cubic-phase CoS₂ nanosheets were prepared on SSF substrate by one-step hydrothermal method.The effect of thiourea concentration in precursor solution on the morphology and electrocatalytic performance of the nanosheets was investigated.It was found that when the concentration of thiourea was 0.083M,the CoS₂prepared was an ultra-thin nanosheet with a thickness of 10 nm.With the augment of the concentration of thiourea,the entropy of the reaction system increased,and the Gibbs free energy minished,which led to the accelerated growth of the nanosheet.As a result,the thickness of the nanosheet augmented rapidly with theincrease of the concentration of thiourea.At the same time,the effective active area of the nanosheets minished,leading to a decrease in the catalytic activity.Co₃O₄ nanowires uniformly loaded on SSF substrates were prepared by hydrothermal reaction and heat treatment.The obtained Co₃O₄ nanowires were vulcanized to obtain cubic phase CoS₂ nanowires.The effect of cobalt chloride concentration and curing temperature on the morphology and electrocatalytic performance of nanowires in hydrothermal solution was studied.It was found that the concentration of cobalt chloride significantly affected the density of nanowires in the process of hydrothermal preparation.With the increase of cobalt chloride concentration,the nucleation density increased,so that the density of nanowires increased with the increase of concentration.In the process of high temperature vulcanization,the conversion degree of Co₃O₄ nanowires to CoS₂ nanowires is the largest when the temperature reaches 500?.At this time,the nanowires are connected together to form a network structure,and the electrochemical performance is also the best.The analysis shows that the CoS₂ nanowires can effectively improve the electron transfer efficiency in the Volmer and Heyrovsky reaction process.The high-density nanowires have larger specific surface area and provide more catalytic activity area.Compared with the CoS₂nanowires,the electrocatalytic activity is further improved.Co₃O₄ nanowires and CoS₂ nanowires were phosphated by high temperature phosphating method respectively to obtain Co P nanowires and P doped CoS₂ nanowires.The influence mechanism of the composition,morphology and microstructure of Co P nanowires,CoS₂ nanowires and P doped CoS₂ nanowires on their electrochemical properties was studied.It is found that Co P nanowires are unstable and coated with a layer of P oxide,which hinders the improvement of electrocatalytic hydrogen evolution activity.The analysis of P-doped CoS₂ shows that the nanostructure is stable and the performance of electrocatalytic hydrogen evolution is excellent.This is because the doping of P exposes more catalytic active sites of CoS₂ and makes the hydrogen adsorption?G_H*of the intermediate closer to thermally neutral.