Synthesis Of Interlayer-expanded Molybdenum Disulfide And Study On The Mechanism Of Hydrogen Evolution Performance Improvrment

The overuse of traditional petroleum energy sources has led to an increasingly aggravated greenhouse effect,causing serious environmental problems.With the proposed of“carbon neutrality”,the development of clean energy has become the main work of relevant scientists.The only product of hydrogen combustion is water,which is a very good clean fuel and has been widely studied.Among the many methods of producing hydrogen,electrolysis of water is an efficient strategy.In order to improve the efficiency of electrolyzed water to hydrogen,electrocatalyst for hydrogen evolution reaction came into being.MoS₂ is rich in reserves and has high marginal activity,while the interlayer widening of MoS₂ will also have a greater impact on its hydrogen evolution performance,so it has attracted widespread attention.This paper aims to develop an interlayer-expanded MoS₂ without the introduction of foreign intercalation molecules,so as to develop a simple,efficient and economical method of widening layer spacing.And the mechanism of hydrogen evolution performance improvement was studied through the experiments and DFT theoretical calculations.The results were as follows:1.A method to synthesize interlayer-expanded molybdenum disulfide micro--flowers（E-MoS₂）by increasing the proportion of thiourea in the reactant was proposed.In this method,ammonium thiocyanate,the product of thiourea conversion in hydrothermal reaction,was embedded into the interlayer of MoS₂ formed in situ to expand the layer spacing,which avoided the complex synthesis process of traditional E-MoS₂ and the introduction of foreign species and templates.The E-MoS₂ has a micron-flower-like morphology and is composed of MoS₂ nanosheets with a wide layer spacing of 0.93 nm stacked in an orderly manner.The reason for the interlayer expansion may be caused by the embedding of ammonium thiocyanate molecules converted by excess thiourea into the MoS₂ layers during the reaction.After the hydrogen evolution performance test,the E-MoS₂ was measured to show good hydrogen evolution activity.At the same time,after 20 hours of constant current polarization test,the hydrogen evolution overpotential of E-MoS₂ has increased slightly,2.A series of DFT calculations for E-MoS₂ were performed.By calculating and simulating the growth of E-MoS₂,it is found that the surface adsorption of ammonium thiocyanate occurs first during the growth of E-MoS₂.In the process of its adsorption,ammonium thiocyanate molecules are wrapped on the surface of MoS₂,reducing the agglomeration performance of MoS₂ particles,thereby refining the grains,accelerating the shape of MoS₂’s nucleus,resulting in an increase in specific surface area,thereby exposing more active positions;and through the calculation of energy band structure and state density,it is further understood that the electronic structure of the material is affected by the presence of NH₄⁺,thereby improving the conductivity of the material,making it have metal characteristics closer to platinum.Therefore,the increase in specific surface area and the improvement of electrical conductivity have led to the improvement of E-MoS₂ hydrogen evolution performance.