Preparation Of Transition Metal Sulfides In Molten Salt And Electrochemical Properties

As a substitute for traditional fossil fuels,research on hydrogen energy will have a revolutionary impact on all aspects of energy utilization.Using the excess energy of renewable energy to drive electrochemical means is an effective way to efficiently produce hydrogen.Recognized as the most effective catalysts for HER and OER（Pt-based materials and Ru-Ir-based oxides）,commercial applications are greatly hindered due to high price and scarcity.Therefore,develop ideal non-precious metal catalysts and find stable and efficient electrocatalysts to realize the filling of transition metal transition orbitals with high intrinsic activity of cost-effective transition metal sulfides（TMS）.The changeable oxidation state makes it flexible.On the other hand,the hydrothermal method is commonly used to synthesize TMS,which has high environmental requirements and is expensive,while the molten salt method is more suitable for promotion in the industrial field due to its simple method and low price.The molten salt method is often referred to as industrial production due to its simple method and low price.Combining the above two points,this study uses the molten salt method to prepare a high-performance dual-functional transition metal polysulfide composite material by rationally regulating the microstructure of TMS.The specific work is as follows:（1）Using foamed nickel（NF）as the nickel source and conductive substrate,supplemented with dilute hydrochloric acid（HCl）pretreatment(dilute hydrochloric acid is used to gradually change the Ni²⁺content on the surface of NF and activate NF)to form the reaction precursor,and then use nine Sodium sulfide in water（Na₂S·9H₂O）is the sulfur source,potassium chloride/lithium chloride（KCl/LiCl）is the molten salt system,molten salt reaction is carried out in an inert gas,and nickel trisulfide is successfully prepared on NF（Ni₃S₂/NF-12）Nanosheet.When the HCl treatment time is 12 h,the Ni₃S₂/NF-12 prepared by the molten salt method has the most excellent OER performance,only 355 mV overpotential can reach a current density of 20 mA cm^-2,and the Tafel slope is only 121 mV dec^-1.（2）In order to solve the problem of low intrinsic activity of Ni₃S₂ and relatively low ratio,ferric chloride（FeCl₃）solution was used to pretreat NF and successfully synthesized iron sulfide/nickel disulfide composite nanosheets（x FeS-Ni₃S₂/NF）.We control the concentration of FeCl₃ solution to participate in the molten salt sulfidation reaction and the content of Fe element,and achieve the control of FeS/Ni₃S₂ composite The purpose of the structure.FeS and Ni₃S₂ form a heterogeneous interface,and their synergy greatly improves the OER catalytic performance of x FeS/Ni₃S₂/NF.When the concentration of the FeCl₃ solution is 0.3 M,the OER overpotential of the prepared 0.3FeS/Ni₃S₂/NF is the lowest.When the current density is 20 mA cm^-2,only 266 mV is required,and the Tafel Slope is 92 mV dec^-1,and the performance Outstanding OER stability.（3）Aiming at the single OER catalytic function of x FeS/Ni₃S₂/NF,it can date both Fe and Co.By adjusting the molar ratio of cobalt chloride（CoCl₂）and FeCl₃ in the pre-solution,the content of Ni²⁺,Fe²⁺and Co²⁺on the surface of the NF participating in the vulcanization reaction is controlled,and the final Co₉S₈/FeS₂/Ni₃S₂/NF-x combination is formed The structure of one-dimensional（1D）nanorods and two-dimensional（2D）nanosheets forms a ring-shaped composite structure.In 1 M KOH electrolyte,when the molar ratio of CoCl₂ and FeCl₃is 2:1,the prepared Co₉S₈/FeS₂/Ni₃S₂/NF-2:1 has excellent HER and OER catalytic activity,and the current density is 20 mA cm^-2.When the current density is 20 mA cm^-2,the overpotentials of HER and OER are 213 mV and 246 mV,respectively,and the Tafel slopes are124 mV dec^-1 and 78 mV dec^-1,respectively.