First-principes Study On The Regulation Of Electrocatalytic Properties Of Phosphorene

Electrochemical water splitting is an important technology to produce hydrogen,which is a renewable clean energy to replace traditional fossil fuels.In order to realize scalable commercial production of hydrogen via electrochemical water splitting,developing low-cost and high-efficiency catalyst is of particular importance.Till now,noble metals,such as Pt and Pt-based materials,are the most efficient catalysts toward the hydrogen evolution reaction(HER)in electrochemical water splitting.However,the high cost and low abundance of Pt in nature damped their wide application in industrial hydrogen production.Developing low-cost and high-efficiency novel catalyst is highly desired for practical implementation in electrochemical hydrogen production.Phosphorene,a single layer of black phosphorus(BP),has been investigated recently as a potential electrocatalyst for HER for its large surface area,high carrier mobility,long carrier diffusion distance,and lone pair electrons in phosphorous atom.In the first chapter,we introduce the application of density functional theory in electrocatalysis.Firstly,the principle and process of electrocatalytic hydrogen evolution reaction are introduced,which can be simply described as water decomposition and hydrogen desorption.The standard hydrogen electrode model is used to calculate and process the potential energy of the electrode,and the adsorption strength between hydrogen and the electrode is quantified by calculating the free energy of adsorption of hydrogen.In addition,Tafel slope and overpotential can be used to analyze the activity of the electrocatalyst.Then the structure and the research progress in electrocatalysis of phosphorene were introduced.The second chapter introduces the density functional theory and its development.Firstly,the theoretical basis of density functional theory is introduced.The Hohenberg-Kohn theorem was proposed by Hohenberg and Kohn based on the Thorms-Fermi model theory.The ground state properties of multi-particle systems are a function of electron density,and all other electron properties of the system can be known from electron density.The ground state electron density can be obtained by iterative method to obtain the ground state energy of the system.In addition,all the approximations in the system can be concentrated in the exchange-related functionals.We introduce several popular exchange-correlation potentials,such as Local Density Approximation and Generalized Gradient Approximation.Using density functional theory to solve practical problems needs to rely on a series of simulation calculation software packages,such as Material studio and VASP.We also briefly introduce these software.In the third chapter,on the basis of first-principles calculations,we demonstrate that the catalytic HER in phosphorene can be enhanced significantly with cobalt intercalations.The Co-intercalated phosphorene is metallic with charge transfer from Co atoms to phosphorene,which could enhance the catalytic activity of phosphorene.In addition,the calculated Gibbs free energy of hydrogen adsorption on Co-intercalated phosphorene bilayer is comparable to Pt(111)surface,independent with the degree of hydrogen coverage.Our study implies that the Co intercalation provides an effective approach to enhance the catalytic HER in phosphorene.In the fourth chapter,we studied the effect of vacancy defects on the structure and properties of phosphorene.Phosphorene structures with different defect concentrations were constructed by introducing single vacancy in different sizes of phosphorene supercells.The electronic properties structure and the free energy of hydrogen adsorption of the defective phosphorene were calculated.It was found that all the defect structures exhibited metallicity after the introduction of vacancies.At the same time,the introduction of vacancies enhances the adsorption of hydrogen of phosphorene.As the concentration of defects increases,the electrocatalytic performance of the surface of the phosphorene is better.Therefore,the vacancy defect can introduce catalytic active sites,which is an effective method for adjusting the electrocatalytic performance of the phosphorene.