Theory Study On The Electronic Structure Of Electrode Surface And The Electrocatalytic Reaction Mechanism From First Principles

Fuel eells convert the ehemical energy of the fuel to electric power by the electroeheniical reaetion,are reeognized to be a promising energy resource.The surface of the catalyst surface plays a vital role in the electrochemical reaction.The research on the electronic structure of electrode surface and the electro-catalytic mechanism has important significance for the synthesis of novel catalytic materials and improving fuel cell performance.The research on the electrode is mainly focused on the experimental research,theoretical research is mainly focused on the metal state,and the theoretical research on the electronic structure of the electrode surface is insufficient.Density functional theory is a kind of research on the electronic structure of the quantum mechanics,and has a wide range of applications in both physical and chemical.The main research work is the calculation of the atomic and electronic structure,the adsorption process,the electro-catalytic oxidation mechanism of small molecule on the electrode surface,with the density functional theory and the periodic slab model,at the level of the moleculars and atoms.The major points and valuable results in this dissertation are summarized as follows:1.In this section,we researched that the atomic layer thickness and vacuum layer thickness have a effect on the the calculation results of periodic plate model,and the design of the electrode physical model by using the method of solid state physics and electrochemical theory.We build the physical model of electrod by changing the charge state of the metal surface model and simulating the movement of the electrode potential,and then calculate the characteristics of electrochemical electrode surface.2.The adsorption and electrocatalytic oxidation of H₂ on the top,bridge and hollow sites of Pt?111?surface are investigated by using density functional theory.The results show that the most favorable molecular adsorption sites is the hollow sites of the electrode Pt?111?surface.The adsorption energy on the electrode surface is more than that on the metallic surface.The bond length of H-H increases.The vibration frequency of H₂ adsorbed is smaller than that of free molecular H₂,namely,a red-shift occurs.The charge transfers from H₂ to Pt?111?surface.The delocalization effect of increases greatly.3.The density functional theory?DFT?and self-consistent periodic calculation were used to investigate the formic acid adsorption on Pd?110?surface.The equilibrium structure,adsorption energy,Mulliken population,and vibrational frequency of HCOOH on three possible sites?bridge,bidentate,uni dentate?on Pd?110?surface were predicted.The computed results show that:the bidentate site is the preferred adsorption site on matel surface,the unidentate site is the preferred adsorption site on electrode surface.The adsorption energy of HCOOH on the surface of the electrode is greater than the metal surface.The bond length of O-H and C-H has elongated.The vibration frequency of v?O-H?and v?C-H?has decreased.Mullken analysis shows that the electron of HCOOH has transferred into the Pd?110?electrode surface.There are two transition states and one adsorption intermediate of the electrocatalytic oxidation of HCOOH on the Pd?111?surface by means of the transition state search of the electrocatalytic oxidation process.The heat of the reaction is-0.7178eV,4.The atomic and electrical structure of Pd?110?and Pd_xFe_y?110?surface were calculated using the density functional theory?DFT?based on the plane wave pseudopotential method.The results show that Fe atomic ratio has little effect on the surface of superficial ruffle?s?,injection charge has a little effect on the surface of superficial ruffle?s?.The electrons has been transferred between Pd and Fe due to Fe atoms doping.Furthermore,the d hole of 4d10 orbital has been increased.The surface charge distribution of the electrode surface is more than that of the metal surface.The s,d,p electronics of the electrode surface decreased with the metal surface.The electrocatalytic reaction activity increased due to the hybridization of Pd and Fe surface electron.5.The density functional theory?DFT?and self-consistent periodic calculation were used to optimize structures,analysis Mulliken population,and calculate vibrational frequency of HCOOH on Pd_0.5Fe_0.5?110?surface by the seven forms of three possible sites?bridge,bidentate,unidentate?.The computed results show that the unidentate site is the preferred adsorption site on the metal and electrode surface.The energy barrier of the transformation between different adsorption forms is small,the formic acid is easy to be transformed between different adsorption forms.The adsorption energy of HCOOH on the surface of the Pd_0.5Fe_0.5?110?electrode is greater than the metal Pd_0.5Fe_0.5?110?surface.The structure and frequency analysis of adsorption on the electrode surface shows that the bond length of O-H and C-H has elongated,and the vibration frequency of v?O-H?and v?C-H?has decreased.H is easy to break,and divorced from HCOOH in the adsorption process.Mulliken population analysis shows that the electron of HCOOH has transferred into the Pd_0.5Fe_0.5?110?electrode surface.The results of calculation show that the electro-catalysis is easier than the ordinary chemieal reactions of the HCOOH on Pd_0.5Fe_0.5?110?surface.There are two transition states and one adsorption intermediate of the electrocatalytic oxidation of HCOOH on the Pd_0.5Fe_0.5?110?electrode surface by means of the transition state search of the electrocatalytic oxidation process.The heat of the reaction is-0.7699eV.Fe atom doping not only has no effect on the catalytic effect of Pd atom,but also contributes to the electrocatalytic oxidation of HCOOH.