Theoretical Design Of Two-Dimentional Materials And Catalysts

With the development of numerical methods and the improvement of computational power,density functional theory(DFT)based first-principles calculation has become an important research method in condensed matter physics,physical chemistry,and materials science.In this thesis,catalytic reaction,materials properties,and experimental phenomena were studied using DFT,involving electronic structure,lattice vibration,optical and mechanical properties.The aim is to provide guidance for the selection of catalyst and the design of high performance photoelectric materials.In the first chapter,we briefly introduce the basic framework of density functional theory and other research tools used in this thesis.By improving the exchange-correlation functional,DFT allows for more and more accurate results.The CHE model and CO2 electroreduction are then introduced.Finally,we briefly introduce the descriptor search methods used in the thesis,including machine learning and SISSO.In chapter two,we focus on the design principle of active center for CO2 electroreduction.In order to design catalyst for CO2 electroreduction rationally and avoid the trial-and-error process,we propose to use the intrinsic properties as descriptors to describe the CO2 reduction activity.We found that the intermediates bound by oxygen atom and by carbon atom have a linear correlation with the binding strength of*OH and*OCH,respectively.Therefore,the high-dimensional problem is turned into a two-dimensional one.The catalytic activity can be obtained only by considering the binding strength of*OH and*OCH.To get the intrinsic factors deterimining the binding strength of*OH and*OCH,we select the physical properties of active center as features to fit the target*OH and*OCH binding strength using a machine learning method.We find that outermost d-shell electron number and enthalpy of vaporization are the main factors that affect the adsorption strength of*OH and*OCH,respectively.We further verify that the two descriptors are applicable not only to two-dimensional materials,but also to single-atom doped metal surface.Our study provides a more convenient way to selecti active center for CO2 electroreduction.As introduced in chapter 3,we theoretically design a class of two-dimensional transitional metal borides(MB2).After scanning all possible transition metal borides,we found 13 stable monolayer.Because of the metal saturated surface,MB2 can activate CO2 molecule spontaneously and reduce them to methane.Among these catalysts,the limiting potential of OsB2 is the lowest one.Non-noble metal catalyst such as FeB2 and MnB2 may also be used in practice.In addition,we found that the binding strength of oxygen atom can be used as a descriptor of CO2 reduction activity.We expect these results to simulate the development of two-dimensional materials for electrocatalytic CO2 reduction.The emergence of graphene makes two-dimensional materials become a research hotspot.In chapter 4,we design two two-dimensional semiconductor materials,PdP2 and PdAs2.They have modest band gaps and high carrier mobilities up to 105cm2V-1s-1.Biaxial stress can be used to adjust the band gap as well as the effective mass of electron.Besides,the strong light absorption strength and wide absorption range are comparable to that of common used optical materials.These outstanding properties make penta-PdP2 and penta-PdAs2 promising in ultrafast electronic and optoelectronic devices.Black phosphorus(BP)is considered to be one of the most promising materials for the next generation of photoelectric devices.In chapter 5,we study the interfacial properties of BP and transition metal carbide(MXene)van der Waals heterojunction(BP/MXene)devices.Because of the metallic properties of MXene,BP/MXene can be used in electron transport devices.In the vertical direction,all BP/MXene heterojunction interface is ohmic contact.In the lateral direction,except for ohmic contact of BP/Zr3C2O2,others have small Schottky barriers.Due to the weak interaction,such van der Waals devices have large tunneling energy barriers at the interface.Except for metal-semiconductor contact,BP/Zr2CO2 can form a type-II contact,which is suitable to the separation of electron-hole pairs.An extenal electric field can be used to regulate the distribution of electrons and holes in the heterojunction.The multiple properties of BP/MXene heterojunction make it possible to be used in electronic devices.In chapter 6,we introduce the cooperative studies with an experimental group,which mainly includes the adsorption behavior of small molecules(CO,H2,HCOOH)on ZnO(10-10)surface.Experimental research found that CO could not be stably adsorbed on the surface of ZnO(10-10),but after CO2 pre-adsorption,CO could be fixed on the surface.Our calculations found that the adsorption strength of CO on CO2 pre-adsobed surface indeed increases compared with the surface without CO2.This phenomenon is mainly caused by more positive charge in adjacent Zn sites due to CO2 adsorption.Experimental research also found that H2 can form stable long chains on the surface of ZnO(10-10)at low temperatures.Our calculations suggest that the formation is a self-catalytic process.After the first H2 molecule being dissociated,other H2 molecules are going to dissociate along dissociated H2 molecule with low barrier to form a stable hydrogen chain.The chain is directional.Computational results explain the experimental phenomenon well.The simulated STM image also agree with experimental results.We also simulate the spontaneous dissociation configuration and the possible short chain configuration of HCOOH molecule on ZnO(10-10)surface.The calculated results and simulated STM images is also consistent with experimental results.