First-principles Study On The Regulation Of Electrical And Electrocatalytic Properties Of Low-dimensional Nanomaterials

Low-dimensional nanomaterials attract a wide range of attention from scientific research institutes and industry due to the reduction in dimension,which induces abundant electrical,optical,magnetic,mechanical,and catalytic properties,but its existing properties are far from satisfying current electronic devices and energy materials.Therefore,the development of new materials and structural regulation based on existing materials are important means to achieve the above goals.This dissertation focuses on single-layer transition metal chalcogenides(TMDs)with novel structures and common energy catalytic materials using first-principles methods to investigate the of electronics and electrocatalytic properties of the material through atomic position reconstruction,defect engineering,surface interface engineering,nanostructure engineering,and single atom.This paper is mainly divided into four parts,divided into five chapters.The first part is the first chapter,which is the theoretical basis of the full text,including the density functional theory(DFT),the basic theory of electrochemistry and the means to deal with the phase transitions.The second part is the second and third chapters.The second chapter mainly investigates the effect of the atomic position reconstruction on the structure and properties of antimony disulfide(ReS2).The third chapter is based on PdSe2,through defect engineering,atomic position reconstruction and the transfer of alkali metals(Li,Na,K)on the surface enrich the properties and utilizations of PdSe2.The third part is Chapter 4,combined with experiments,to investigate the effects of surface defect engineering,nanostructure engineering,surface interface engineering,and single atoms on common electrocatalytic reactions such as oxygen reduction reaction(ORR),oxygen evolution reaction(OER),hydrogen evolution reaction(HER),and CO2 reduction reaction(CRR).The first chapter mainly introduces DFT,the theoretical basis of electrochemistry and the knowledge of solid phase transition.The full text is based on the DFT,using the corresponding ab initio software package to self-consistently solve the single particle KS equation,and the multibody interactions in the actual system are embodied in the exchange-correlated items,and listed the types of exchange-correlation functionals and the corresponding applicable conditions.The electrochemical theory part is mainly based on the standard hydrogen electrode model,pointing out the influence of the electrode potential on the reaction free energy and the activation energy barrier.Among them,the influence on the reaction energy barrier is enumerated by common treatment methods,such as equal electric potential through injection of charge-regulating electrode potential;Equipotential electrode potential method based on double layer capacitance in electrochemical;Regulation of energy barrier based on Butler-Volmer equation.The search for the corresponding transition state energy barriers is mainly LST/QST,CI-NEB and Dimer.Finally,from the perspective of thermodynamics and dynamics,we have enumerated the common ways of phase transition.The second chapter introduces a new phase of ReS2 with tunable magnetism.It can be used to transform the rhombohedral phase(DT phase)of ReS2 to the Trimer phase(Tri phase)through the movement of Re atoms in the intermediate layer.This can be achieved by intercalating lithium or injecting charge.The ground state of the Tri phase is a bipolar magnetic semiconductor.The injection of charge can realize the half metal transformation.Based on the Ising model Monte Carlo simulations,the Curie temperature is 157K,and the carrier impurity can be raised to above room temperature.The direct exchange between Re atoms leads to ferromagnetic coupling and induces strong magnetic anisotropy energy(5.716 meV/atom).The third chapter is mainly the series of single-layer PdSe2 work.For the first time in recent experiments,a two-dimensional material with a pentagonal structure has been synthesized.There is a groove structure similar to the phosphene fold.Calculations show that there is also an ultra-fast alkali metal(Li,Na,K)migration channel along the direction of the trenches,the energy barrier sizes are 0.176,0.141,and 0.090 eV,respectively.Because the defects in the experimental synthesis process are unavoidable,we studied the effect of the simplest intrinsic point defects on the performance of PdSe2.Point defects include vacancy,antisite,interstitial,and Stone-Wales defects.In the last work,the formations of new phases of PdSe2 were investigated.Since the five-membered ring contains a unique Se-Se bond,a series of new phases was reconstructed by the rotation of the Se-Se bond.The gaps are all smaller than this anisotropic pentagonal phase through HSE06 calculations,but the carrier mobilities are higher than this phase.The SSNEB calculations show that the transition energy barrier between them is less than 0.1 eV/atom,and it is also proposed that the new phases can be obtained by chemically etching K+ and Na+ in K2PdSe2 and Na2PdSe2.The fourth chapter deals with the work of structural regulation on the performance of electrocatalytic reactions.The main results are as follows:(1)The Au@Pd@Pt core-shell structure was designed by crystal surface engineering.It was found that the higher the crystal face index,the higher the oxygen reduction activity,and the core-shell structure also enhanced the adsorption and activation of O2.(2)To study the influence of interface engineering on the hydrogen evolution reaction(HER),oxygen evolution reaction(OER)and oxygen reduction reaction(ORR).With the help of solid oxide fuel cell cathode material Lanthanum strontium cobalt ferric,it was found that the boundary layer formed by segregation of cerium carbonate greatly enhances the activation of O2.The interface formed by the precipitation of Ag particles in the delafossite AgCoO2 enhances the OER performance,and proposes an enhancement mechanism of interfacial charge states,mainly contributed by delocalization s orbitals of Ag;The interface formed by the PdMnCo ternary alloy and N-doping carbon induced confinement effect.greatly enhances the HER performance;the Fe-Ni3S2 obtained by in-situ sulfidation of the Ni-Fe alloy is superior to Ni3S2,the calculation of the density of states shows that the surface has a more abundant delocalized charge.(3)The last three jobs involving structural nanotechnology,defect engineering,and monoatomic methods to regulate the Co3O4 to achieve CO2 electrocatalytic reduction to formic acid.The details are the ultrathin?9A,oxygen vacancies,and monoatomic Pt limits of nanoplatelets.The reaction in two-dimensional confined space greatly enhances the activity and selectivity of the reaction.The last chapter is a summary of the full text,referring to the limitations of the current simulations,pointing out the research interests of the next age.