Preparation Of Nickel And Molybdenum Disulfide Composites And Their Electrocatalytic Performance For Hydrogen Evolution

In recent years,the depletion of fossil energy has brought the world into an energy crisis.Therefore,the development of a green,clean and renewable energy source is imminent.As a clean and efficient energy,hydrogen energy has attracted the attention of many scholars.Due to its abundant raw materials and pure products,the method of producing hydrogen by electrolyzing water is considered as an effective method.The noble metal catalysts such as Pt exhibited excellent electrocatalytic performance,but their high prices and scarce reserves limit their large-scale applications.Therefore,this is an important research topic for scholars to develop an efficient and inexpensive hydrogen evolution catalyst.In recent years,molybdenum disulfide has become a hot topic due to its abundant resource reserves,and its edge structure has similar catalytic activity as Pt.However,the poor conductivity and the slow reaction kinetics of molybdenum disulfide in alkaline systems remain to be solved.While metallic nickel has high catalytic activity and conductivity in alkaline systems,its easy-to-agglomerate properties greatly reduce active sites.And many researches have shown that the strong adsorption of hydrogen atoms by nickel metal also limits the improvement of performance.In view of the above problems,Ni and MoS₂ are combined in this article to obtain a Ni-MoS₂ electrode with good dispersion to improve the conductivity of the material,increase the number of active sites,and improve the overall catalytic activity of the material.The research achievements of this paper are as follows:?1?In this paper,MoS₂/CC materials were synthesized by hydrothermal method using ammonium molybdate as molybdenum source and thiourea as sulfur source.The optimum molybdenum disulfide loading substrate was selected by morphology and electrochemical characterization.Then,Ni-MoS₂/CC composite electrode was prepared by depositing metallic Ni on the surface of MoS₂/CC by cyclic voltammetry,and the deposition amount of Ni was adjusted by controlling the number of scanning cycles of cyclic voltammetry.The experimental results show that when the number of scanning cycles is 20,the Ni-MoS₂/CC electrode material exhibits the best catalytic activity,which is attributed to the multi-pleat structure of the MoS₂/CC substrate provides more growth sites for Ni,and the synergy between them also enables Ni particles to be effectively refined and expose more active sites.In addition,the more edge structure exposed on the MoS₂/CC substrate is also one of the reasons for the improved catalytic performance.?2?Based on the experimental results,the activity origin of Ni-MoS₂ electrode materials was discussed using density functional theory?DFT?.The calculation results show that,in terms of structure,the growth of Ni is more likely be tiled on the MoS2surface rather than aggregating into large particles like pure Ni.This change makes the dispersion of Ni more uniform and thus significantly boosted the number of electrochemically active sites.And by changing the coverage of Ni in the Ni-MoS₂ model,it is found that the stability of the model is not destroyed.In terms of performance,the adsorption of Ni atoms narrows the bandgap of the material,and causes an impurity state appears near the Fermi level,which makes the system exhibit a semi-metallic property that facilitates electron transport.In addition,the results of the d-band center show that the presence of MoS₂ weakens the strength of H adsorption on the surface of metal nickel,which demonstrates that the subsequent recombination and release process of H in Ni-MoS₂ catalyst is relatively easy.The negligible coupling between the Ni atom and the MoS₂ is one of the reasons why the overall hydrogen evolution activity of the material is improved.Through the calculation of the free energy of H atom,the adsorption and desorption of hydrogen atoms on the surface of Ni atom tend to balance.And as the amount of adsorption of hydrogen atoms increases,the free energy of H atoms becomes smaller and smaller.