Structural Design And Applications Of Novel Two-Dimensional Chalcogenides

With the increasing of energy crisis and environmental pollution,designing and researching energy storage materials have been used as two important ways to solve energy issues.In recent years,because of the wide variety of two-dimensional?2D?structures and their different properties,they have shown interesting application prospects in many fields,such as optoelectronics,spin electronics,superconductors,catalysis,and rechargeable lithium batteries,etc.Among diverse 2D materials,2D chalcogenides arouse great interest due to many unusual physics,chemical or electronic properties.In particular,they have some unique properties:Firstly,they have a large specific surface areas,which provide more active sites.Secondly,the electronic structure can be easily tuned by applying the external stress,electric fields,quantization effects of edge,reduction in thickness,lattice symmetry and dimension.Thirdly,they exhibit relative high electron mobility,which make them more promising in the field of energy storage and conversion.Therefore,controling and desiging novel 2D chalcogenides with diverse properties is of great research significance.The research contents of this article are as follows:?1?The dimensional and hydrogenating effect on the electronic properties of ZnSe nanomaterial:a computational investigation2D large-area freestanding ZnSe monolayer has been fabricated,it has unique electronic structure and an excellent structural stability,the band gap value is 2³ eV,showing excellent electrochemical properties.In this paper,we performed a comprehensive study on the structure and electronic properties of ZnSe two-dimensional?2D?nanosheets and their derived one-dimensional?1D?nanoribbons?NRs?and nanotubes?NTs?.Both hexagonal and tetragonal phases of ZnSe?h-ZnSe and t-ZnSe?were considered.Theoretical calculations show that the tetragonal phase is thermodynamically more favorable for 2D monolayers and 1D pristine nanoribbons,in contrast,the hexagonal phase is preferred for the edge-hydrogenated 1D NRs and NTs.In terms of electronic properties,both h-ZnSe and t-ZnSe monolayer appear as direct bandgap semiconductors.The pristine zigzag nanoribbons?z-hNRs?and the corresponding edge-hydrogenated NRs gradually convert from the direct-bandgap semiconducting phase into a metallic phase as the ribbon width increase.The pristine armchair nanoribbons?a-hNRs?remains as semiconductors with indirect bandgaps with increasing ribbon width,and edge hydrogenating switches the indirect-bandgap feature to the direct-bandgap character or metallic character with the different edge passivation styles.While the pristine and edge passivated t-ZnSe nanoribbons still maintain the direct-bandgap character.The1D h-ZnSe and t-ZnSe nanotubes keep the direct-bandgap semiconducting property but with smaller bandgaps.Our systemically study provides deep insight into the electronic properties of ZnSe nanomaterials and is helpful for experimentalists to design and fabricate ZnSe nanoelectronics.?2?Metallic FeSe monolayer as anode materials for Li and Non-Li ion batteries:A DFT studyThe electronic properties of the FeSe monolayer are metallic,high conductivity and good structural stability.In this section,by means of density functional theory computations,we explored the electrochemical performance of the monolayer FeSe as anode materials for lithium and non-lithium ion batteries?LIBs and NLIBs?.The electronic structure,adsorption,diffusion,and storage behavior and average open-circuit voltage of different metal atoms?M=Li,Na,K,Mg,and Ca?on the FeSe were systematically investigated.Our computations revealed that the FeSe monolayer have high rate performance,?the diffusion energy barriers are 0.16,0.13and 0.11 eV for Li,Na,and K,respectively?,storage capacity(658,473,and 315 mA h g^?1 for Li,Na,and K)and moderate average open-circuit voltage?OCV,0.38⁰.88eV?.All these characteristics suggest the FeSe monolayer is a potential anode material for alkali-metal rechargeable batteries.?3?The structural design and application in photocatalytic of two-dimensional pentagonal transition metal dichalcogenidesSeeking novel materials with specific applications is always an attractive theme in developing 2D nanomaterials.Herein,we theoretically proposed ten kinds of single-layer pentagonal transition metal dichalcogenides penta-MS₂?M=Mn,Ni,Cu/Ag and Zn/Cd?sheets with?and?phases.These penta-MS₂ sheets are dynamically,mechanically and thermally stable,and have diverse electronic properties,covering direct bandgap semiconducting,indirect bandgap semiconducting and metallic characters.The mechanical properties show low Young's modulus?8⁹4 N/m?and negative Poisson's ratio in plane.Among them,the semiconductors penta-MS₂?M=Mn,Ni,Zn and Cd?have suitable bandgaps?2.01³.67 eV?and band egde positions can perfectly satisfy the redox potentials of photocatalytic water splitting via strain engineering.Meanwhile,they exhibit strong light absorption coefficients(up to 10⁵ cm^-1)with obvious absorption peaks in the visible region,favorable for the utilization of sunlight.These results indicate that the penta-MS₂ family has potential applications in the fields of flexible devices,optoelectronics,and photocatalysis.?4?The structural design and electrical,mechanical properties of 2D SN₂ monolayerBy means of density functional theory?DFT?computations and global structure search,we theoretically predicted a novel 2D SN₂ monolayer?S-SN₂?structure.In the S-SN₂ monolayer,each S atom is tetracoordinated with four N atoms,and each N atom bridges two S atoms,forming a tri-sublayer structure with square lattice.The monolayer exhibits good stability,as demonstrated by the thermodynamics,kinetics,and thermal.It exhibits rich electrical and mechanical properties in nature:an indirect-bandgap semiconductor with high hole mobility,and the bandgap can be tuned by changing the thickness and external strains?the indirect-bandgap to direct bandgap transition occurs when the biaxial tensile strains reaches 4%?.Mechanically,it has larger Young's modulus?279.82 N/m?and three-dimensional auxetic properties?both in-plane and out-of-plane negative Poisson's ratios,-0.104?.Therefore,the S-SN₂ monolayer holds great potential applications in electronics,photoelectronics and mechanics.