First-principles Study On The Low-Dimensional Donor-Acceptor Heterostructures Catalysts

The discovery and development of two-dimensional materials have greatly enriched people's understanding of the structures and properties of matter.A large number of two-dimensional materials have emerged new physical and chemical properties due to their quantum effects,dimensional effects,surface effects and others.These developments have inspired both theorists and experimentalists to produce new theories,new concepts,new technologies,and new applications.Two-dimensional materials have various of applications in basic physics,applied physics,chemistry,energy,materials,and biology.Some fascinating directions include the development of low-dimensional heterostructures and the application of two-dimensional materials in energy conversion have drawn intensive attention.For example,compared to traditional semiconductor heterostructures and superlattices,van der Waal s heterostructures composed of two-dimensional materials are not limited by lattice mismatch,interface bonding,interface defects,surface states and other factors,therefore,the clean interface,the sharp electronic state,and amount of material combination possibilities could be achieved.The richness of heterostructure's structures and properties will increase by several orders of magnitude.A highlighted example is the magic angle twisted bilayer graphene.The unexpected correlated states and superconducting states that appear in such systems are important advances in condensed matter physics in recent years and pioneered the new direction so-called"twistronics".For another example,the progress of two-dimensional materials in energy conversion,especially catalytic reactions,has attracted intensive attention both academic and industry society in this field from fundamental research to laboratory demonstration to industrialization.In this thesis,first-principles calculation methods based on density functional theory are performed to study the electronic structure of low-dimensional heterostructures,and a new type of "donor-acceptor heterostructure"is found except the traditional heterostructure and van der Waals heterostructure.The interaction strength between the layers is a moderate "quasi-bond".We have studied the mechanism of the combination of the two layers and give a physical picture of the energy competition.Besides,we studied the activation of the greenhouse gas carbon dioxide molecule on the donor-acceptor heterostructures.The adsorption energy barrier and the Gibbs free energy diagram of hydrogenation are calculated.The explanation of the activation mechanism is given.Furthermore,since of the high specific surface area and high density of active sites of the two-dimensional materials,we studied the graphene-supported single transition metal atom catalyst electrocatalytic carbon dioxide reduction and fuel cell cathode oxygen reduction,and obtained excellent reaction activity and high selectivity.There are five chapters in this thesis.The first chapter is an introduction to first-principles computational materials science and electrochemical calculation methods.The Schrodinger equation in quantum mechanics is briefly introduced,and various approximations and assumptions need to be adopted to apply it to many-electron solids.Among them,the density functional theory based on the Born Oppenheimer approximation and the single-electron picture gives a compromise of calculation accuracy and computational resources,which is also the theoretic basis of all calculations in this thesis.The electrochemical reaction on the surface of the material involves the electrochemical model and Gibbs free energy.A brief introduction to the computational hydrogen electrode model,the Gibbs free energy calculation method and the search method of transition states are presented.The second chapter is about the donor-acceptor heterostructure.We calculated the heterostructure which formed via the combination of a variety of single-layer two-dimensional materials,including graphene,hexagonal boron nitride,g-C3N4,and the substrate contains one-dimensional electrides,two-dimensional electrides,transition metals,alkali metals,etc.We have studied the heterostructures composed of these two-dimensional materials,including traditional interface bonding heterostructures,and van der Waals heterostructures with no bonding at the interface.In addition,we have also discovered a new type of heterostructure,the"donor-acceptor heterostructure".We have systematically studied the structure,electronic properties,inter-layer interaction mechanism of this type of heterostructure,and comparison with van der Waals heterostructures.The phase transition between the two heterostructures,and an energy competition model are given.The third chapter investigate the activation and electrochemical reduction of carbon dioxide molecules on the donor-acceptor heterostructures.Starting from the energy level of the carbon dioxide molecules,we analyze the reasons for the difficulty in activation.The adsorption of carbon dioxide molecules on two-dimensional material such as hexagonal boron nitrogen is tested.After comparison the adsorption of carbon dioxide on the monolayer boron nitride and the boron nitride in the donor-acceptor heterostructure,it is found that the carbon dioxide molecule achieved chemical adsorption on the donor-acceptor heterostructure.To understanding the details about adsorption,we have searched the transition state from physisorption to chemisorption,based on the energy barrier and the change of Gibbs free energy before and after adsorption,we postulate the activation mechanism and the physical picture.The subsequent Gibbs free energy diagram of the carbon dioxide reduction shows that the activated carbon dioxide molecule also exhibits the high activity of formic acid and the selectivity of inhibiting the hydrogen evolution reaction in the hydrogenation on donor-acceptor heterostructures.The fourth chapter is the application of single transition metal atom catalyst supported by two-dimensional material in electrocatalysis.The carbon dioxide activation on the donor-acceptor heterostructures occurs on the non-metallic boron atom,while the transition metal atom has partially occupied d orbital so that it has more room for electronic structure regulation.On the other hand,in order to improve the utilization rate of the metal atom,we studied the electrochemical performance of single atom catalyst which is characterized by single transition metal atom anchored on graphene.Including 1.The high CO selectivity of single atom Ni-N4-C system in carbon dioxide reduction;2.The high activity of single atom Fe-N4-C system in cathodic oxygen reduction in proton exchange membrane fuel cells.The fifth chapter is the summary and perspective.The shortcomings and limitations of projects in this thesis are pointed out.And put forward some future work directions and problems to be solved.