Rational Design Of Two-dimensional Materials In Electrocatalysis And Photocatalysis

Energy is an indispensable part of our daily life while over dependence on fossil energy brings a vital global challenge because fossil fuels are rapidly decreasing and are not environmental-friendly.Considering the severe air pollution and carbon dioxide emissions from the combustion of hydrocarbon fuels,hydrogen is recognized as an ideal clean alternative to integrate renewable energy systems and achieves sustainable development in the field of energy storage and conversion.The ideal hydrogen cycle process is that hydrogen is produced by water splitting under the help of solar energy,reversibly stored in solids,and utilized to generate electronic energy in fuel cells.The popularization of hydrogen technology still faces a series of challenges although hydrogen economy and technology have developed rapidly since 1990s.Meanwhile,two-dimensional(2D)nanomaterials are emerging due to their unique physical and chemical properties.Since graphene was first reported in 2004,various synthetic methods have been designed to strip different 2D materials.Besides,different modulation strategies,such as heteroatom doping,defect engineering,and phase engineering/interface engineering,can further enrich the performance of 2D materials,making them play unique roles in the next generation of clean energy conversion systems.In this paper,we explored the potential applications of a series of 2D materials with specific motifs in electrocatalysis and photocatalysis through thermodynamic and dynamic analysis and characterization from the density functional theory(DFT)calculations.The main contents are as follows:In Chapter 3,we investigated the feasibility and activity of 2D planar ?-conjugated metal-organic framework nanosheets,lithium-modified borophenes and heptazine-based graphitic carbon nitride in hydrogen preparation,storage and purification,respectively.The intrinsic holes of 2D materials are potentially active sites to bind metal atoms for catalysts and hydrogen storage and pathways to separate specific gases.In Chapter 4,we investigated the microscopic mechanism of photocatalytic water splitting by a class of asymmetric 2D materials.Compared with traditional photocatalysts,breaking the symmetry of atomic structures on both sides of 2D materials can induce intrinsic dipole moments,which will lead to a significant bending of energy band edges,thus fulfilling the requirement of water redox potential.In addition,the asymmetric structure will generate a built-in electric field which can be used as a booster for exciton separation and diffusion into different surfaces.This method can break the limitation of band gap and expand the spectral absorption range from visible light to near infrared light,so it is helpful to further enhance the photocatalytic activity of solar photolysis water for hydrogen and oxygen production.In Chapters 5 and 6,we explored the potential applications of ?-? 2D materials in hydrogen-oxygen fuel cells and lithium-oxygen batteries,respectively.We found that due to the electronegativity difference of elements in binary material system,the surface of binary alloy 2D material will spontaneously generate Lewis acid-base sites,which facilitates the adsorption and decomposition of oxygen and weakens the adsorption of carbon monoxide.Based on the thermodynamic analysis,these materials are promising to replace platinum-based catalysts,and expand the application of 2D non-metallic materials in electrochemistry.