Preparation Of Molybdenum Disulfide Based Two-dimensional Materials And Their Application In Energy Conversion And Storage

With the rise of two-dimensional materials research,two-dimensional（2D）transition metal dichalcogenides（TMDs）,represented by molybdenum disulfide（Mo S₂）,are the most promising materials for human beings due to their unique physical,chemical and electronic properties for energy and environmental issues.Surface activation and structural design have gradually attracted attention and become a research hotspot due to their great improvement in the intrinsic activity,atomic utilization,and interfacial charge transfer to Mo S₂,and have extremely high application prospects in the field of energy storage and conversion.For example,single-layer or few-layer Mo S₂has high electrocatalytic hydrogen evolution（HER）activity at its edges,which has great applications in electrolysis of water for hydrogen production;while Mo S₂nanosheet arrays with three-dimensional spatial structure possess ion storage capacity.It can be used as positive and negative electrode materials for ion batteries.Based on this,this paper aims to regulate molybdenum disulfide-based materials from three aspects:comprehensive preparation method,structural analysis and application exploration,and improve its application scope in different fields.The main contents are as follows:（1）The synergistic effect of Pt nanoclusters and Sv-Mo S_2-xenhances the electrocatalytic hydrogen evolution performanceSingle layer or few layer Mo S₂has a great application in electrolysis of water for hydrogen production because of its high electrocatalytic hydrogen evolution（HER）activity at its edges.In this study,an electrocatalytic hydrogen evolution catalyst with Pt atoms supported on Sv-Mo S_2-xnanosheets by a simple impregnation method was prepared at room temperature.Firstly,the bulk Mo S₂was efficiently exfoliated by the solid-phase reduction method to obtain nanosheets containing a large number of vacancies,and then the Pt atoms were uniformly dispersed on the catalyst surface to form 2-3nm nanoclusters by the impregnation method using its strong carrier effect.Through tests,it is found that when the mass loading of Pt is 5%wt,the utilization of Pt atoms can be maximized,and the overpotential of Pt/Sv-Mo S_2-xat 10 m A cm^-2is only 26.6 m V;Through experiments and mechanism analysis,it is believed that the synergistic effect of Pt nanoclusters and sulfur vacancies can greatly reduce the Gibbs free energy of adsorbed H on the surface of the catalyst,which can effectively promote the activity of HER.Finally,the reason for its good stability is revealed by XPS and TEM to the used catalysts.（2）Covalent functionalization of Mo S_2-xnanosheets with TAPP and their photocatalytic carbon dioxide photocatalysisThe photocatalytic reduction of CO₂is an important way to reduce the greenhouse effect and improve the resource utilization of CO₂.Mo S₂,as a typical semiconductor material,has a strong reduction ability of CO₂by photogenerated electrons.Effectively improving the photogenerated electrons of two-dimensional Mo S₂nanosheets is the key to improve the reduction efficiency of CO₂.In this chapter,we present a method to construct dye-sensitized 2D Mo S_2-xnanosheets by reacting tetraaminophenylporphyrin（TAPP）diazonium salt with Mo S_2-xto form sulfur-carbon bonds.Characterizations such as FTIR,XPS,UV-vis and TEM revealed that a large number of TAPP molecules were chemically anchored on the Mo S_2-xnanosheets through S-C bonds,which could greatly reduce the spatial distance between the TAPP molecules and the Mo S_2-xnanosheets.The photoelectrons generated by TAPP which as a photosensitizer after absorbing light energy can be effectively injected into the conduction band of Mo S_2-xand promote the reduction reaction.Experiments show that TAPP@Mo S_2-xcan reduce CO₂to CO under illumination,and the efficiency is 5.6 times higher than that of Mo S_2-x.The covalent functionalization strategy of molybdenum disulfide and organic small molecules provides a new idea for expanding the application of Mo S₂-based catalysts in photoelectric catalysis.（3）Preparation of hydrated Mo S₂nanoarrays and their application in aqueous zinc-ion batteriesMo S₂nanosheets have controllable layer spacing and their large layer spacing is beneficial to improve the storage capacity of zinc ion,so they are an ideal cathode material for zinc ion battery（ZIBs）.In this work,we prepared Mo S₂-180 by a low-temperature hydrothermal method and investigated its electrochemical properties as a cathode material for ZIBs in aqueous and non-aqueous electrolytes.The characterization results show that the molybdenum sulfide synthesized at low temperature has a low crystallinity and a crystal water content of 13.2%,which is the reason for its larger interlayer spacing.In addition,the specific capacity of Mo S₂-180in aqueous electrolyte is 220 m Ah g^-1,which is much larger than that in non-aqueous electrolyte(40 m Ah g^-1).In addition,in order to reveal the zinc storage mechanism of Mo S₂-180,the electrochemical AC impedance spectroscopy experiment was used to calculate the interfacial activation energy of zinc ions in different electrolytes and different cathode materials,and the crystal water in the cathode material was explained from the thermodynamic aspect.It can greatly reduce the interfacial desolubilization energy of hydrated zinc ions and give a faster intercalation kinetic rate.