| Density functional theory methods,combining with computer softwares to design new materials and to provide with guidance and verification of experimental works,have developed rapidly and perfectly,thus achieving important breakthroughs.After exploring and searching for reasonable and novel materials from the angle of the atomic scale,we confirm materials' structures and test properties based on the first principles calculation.Designing new materials with special performance for experiments is in favor of applying them into actual industrial production.People are faced with severe shortage of resources and environmental pollution resulted by fossil fuel consumption.It's really urge for people to look for clean and sustainable green energy.Electrochemical reactions achieve interconversion between chemical energy and electrical energy,which splites water into hydrogen and oxygen efficiently and supply electrical energy by the hydrogen comsuption.The whole process is not only a zero emission,but also an effective way to reduce greenhouse gas emissions and maintain social sustainable development.Because of the resistance of electrochemical hydrolysis reaction,catalysts are needed to improve efficiency and quality.Nanomaterials,owing to their unique structural characteristics and excellent properties,are often used in the field of catalyst materials.These nano-materials technologies promote the catalytic activity on the surface of the low dimensional and new functional materials,which exposes important significance for people to comprehend the catalytic reaction mechanism and search for new type of nanometer catalysts.Understanding the nature of catalytic hydrolysis of low dimension materials from the angle of the atomic scale by the first principles calculation can guide us design low-cost and highly active nano hydrolysis catalysts.This article designs for a class of one-dimensional molybdenum sulfide nanowires,namely Mo2S6,Mo3S6 and Mo6S10 nanowires.Their lattice structures,electronic properties,mechanical properties and catcalytic effect of hydrogen evolution reaction were explored.The dissertation is divided into four chapters,showing as follows:The first chapter introduces the density functional theory briefly;the second chapter deals with the mechanism of hydrogen evolution reaction from molybdenum sulfide hydrolysis and the free energy reaction mechanism;The next chapter studies structure and performance of Mo2S6 nanowires materials by the first principles calculation;The last chapter introduces structural studies and performance one-dimensional Mo3S6 and Mo6S10 nanowire materials by the first principles calculation.The specific contents are as follows:The first chapter mainly introduces the density functional theory.First,the development of density functional theory is introduced starting from quantum mechanics,which is that the inter-action multi-particle problem can be effectively transformed into the problem of non-interacting particle system by solving the Kohn-Sham equation.All the approximations are all concentrated in the exchange related functionals.The self-consistent iterative method is used to obtain the ground state electron density of the system.After the ground state particle energies of system being solved,and the other properties of the system are calculated.Second,the rapid development of commercial software packages for the realization of the first-principles calculation provide much more effective means of sucessfully to comprehend the nature of the specific system based on computers.The software packages used in some of the theoretical calculations in this paper are introduced at the end of this chapter.In the second chapter,the mechanism of hydrogen evolution reaction(HER)of the molybdenum sulphide nanomaterials was investigated.The significance of hydrogen firstly is introduced as an ideal energy carrier for future social development and environmental improvement.The mechanism of hydrolysis of hydrogen production are expounded by electrochemical method in different pH solutions.Because of abundant resources and stable efficient catalytic efficiency,transition metal dichalcogenides can replace precious metals,such as platinum as a HER catalyst used in the industrial production of Hydrogen.In many transition metal dichalcogenides,Molybdenum disulphide(MoS2)has rich nano-structure and electronic structure.There are two main ways expoesd by experiments and theoretical calculations to promote and improves efficiency of the HER catalytic of MoS2:The first is increasing the quantity of sites on catalyst surface,the second is changing phase of MoS2 and electronic structure.The methods to calculate hydrogen free energy(?GH*)and the criterias to judge molybdenum catalyst performance are expounded in this paper.the zero-points energy used in the calculation of DFT are also describes at the end of this chapter.In the third chapter,the structural characteristics,electronic properties and HER catalytic performance of ID Mo2S6 nanowires were revealed by the first-principles calculations.Firstly,the calculated phonon spectrum which shows no frequency determined the lattice stability of the lowest energy state configuration of Mo2S6 nanowire.Subsequent molecular dynamics simulations confirmed that the 1D Mo2S6 nanowires were thermodynamically stable at least at 600K.In this way,the stability of Mo2S6 ultrafine nanowires was determined from energy,lattice stability and thermodynamics stability.After calculating the elastic modulus of one-dimensional Mo2S6 nanowires,the elastic modulus is 21.33 eV/A,which shows the 1D Mo2S6 nanowires extremely low capacity resistance to deformation.When computing the electronic structure of Mo2S6 nanowire,it was learned to be a semiconductor with the direct bandgap width of 1.55 eV.When calculating the ?GH*on the surface of the HER adsorption site of the Mo2S6 nanowire,the ?GH*of SB1 site is-0.05 eV,which is very close to 0 eV,meaning that the 1D Mo2S6 nano wire have potential application value for HER catalytic applications.There were weak interactions between the two Mo2S6 nanowires,ie Van der Waals force,which reduced the bandgap width to 0.97 eV and weaken the catalytic performance of the HER at the best adsorption sites of the Mo2S6 nanowires.The fourth chapter mainly discusses the first-principles calculation on 1D Mo3S6 and Mo6S10 nanowires and describes their structural characteristics,electronic properties and HER catalytic performances.The calculated phonon spectra of the losests energy configuration of the Mo3S6 and Mo6S10 nanowires were measured without imaginary frequency,indicating that the two nanowires have lattice stability.Molecular dynamics simulations confirmed that the Mo3S6 and Mo6S10 nanowires were thermodynamically stable at least at 600K.In this way,Mo3S6 and Mo6S10 nanowires show stable from energy,lattice stability,and thermodynamics stability.In terms of mechanical properties,the elastic modulus of Mo3S6 and Mo6S10 nanowires were calculated to be 103.22 eV/A and 163.00 eV/A,respectively,showing the extremely soft mechanical properties,and their abilities to resist deformation increases with the increasing width of 1D nanowires.When calculating the electronic structures of Mo3S6 and Mo6S10,we know that Mo3S6 is a semiconductor with the indirect bandgap width of 0.46 eV,while Mo6S10 nanowirc exhibits metallic properties.The ?GH*of the Mo3S6 surface adsorption site Si was calculated to be 0.16 eV,while ?GH*of the Mo6S10 surface adsorption site Siwas 0.30 eV.Comparing the ?GH*calculated by the adsorption sites of three nanowires with different widths of Mo2S6,Mo3S6 and Mo6S10,it was deduced that as the width of the 1D nano wire structure decreases,the calculated ?GH*at the adsorption site is closer to 0 eV,meanting the better the catalytic performance of HER. |
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