Theoretical investigation on chemical interactions of O2 and H with defects of MoS2 monolayer

Abstract

In the past few years, monolayer molybdenum disulfide (MoS2) has gained huge attention due to exotic electronic, optical, mechanical and chemical properties and there have been many studies for application in various fields. In particular, applied researches in chemistry have been actively carried out because defect engineering of monolayer MoS2 is relatively easy. For example, monolayer MoS2 shows interesting gas sensing properties such as oxygen and good catalytic efficiency of hydrogen evolution reaction. However, there are limits to improve efficiency of the chemical reactions without fundamental understanding of mechanism because chemical reaction occurs in atomic scale region. For the fundamental understanding, theoretical investigation can act as key role and the calculation technique based on density functional theory is suitable to reveal the atomistic origins of experimental discoveries. In this thesis, I present theoretical investigations of chemical interactions of O2 and H with defects of MoS2 monolayer. First part is theoretical investigation of O2 sensing mechanism on edge of MoS2. I suggest that O2 molecule can be reversibly adsorbed to bridge site of Mo edge with S monomer and the adsorption of O2 makes flatten band of edge state and it is origin of O2 sensing mechanism of MoS2. Second, I investigate hydrogen evolution reaction on sulfur vacancy of MoS2 monolayer by our theoretical model. I model hydrogen evolution reaction on sulfur vacancy of MoS2 monolayer by considering population of all possible states of sulfur vacancy and turnover frequency of all possible paths. From the theoretical model, I directly estimate polarization curve of hydrogen evolution reaction on VS of MoS2 monolayer and the results are in good agreement with experimental reference. In addition, I investigate strain effect on efficiency of hydrogen evolution reaction on the sulfur vacancy by the theoretical model. From the studies, I can suggest that tensile strain has a good influence to efficiency of hydrogen evolution on sulfur vacancy by increase of population of [2H-VS]1- and decrease of total reaction barrier. By the strict theoretical investigations, I can understand fundamental origin of the chemical interactions and suggest design rules to improve efficiency and performance of application using the chemical interactions.