Theoretical Calculation Studies On The Electrocatalysis Reaction Of Oxygen And Hydrogen And Lithium Iron Phosphate Electrode

Density functional theory(DFT)has been widely used in electrochemical research in recent years.Due to the limitation of computing resources and time,the structural model of DFT calculation is very different from the real structure of the experimental system in terms of scale and complexity,so the result is often difficult to compare directly with the macroscopic experimental results.The Monte Carlo(MC)method is an effective way to communicate between microscopic state and macroscopic phenomena.The statistical average of the large number of samples makes a better match between theory and experiment.In this paper,DFT calculation and MC simulation are combined to study the important electrochemical processes related to energy conversion.The idea of this essay is to construct the forcefield of the electrochemical system by using DFT calculation and cluster expansion(CE)method,and on the basis of which,the Monte Carlo simulation is used to determine the energy and entropy of the electrochemical system and its relationship with the geometry.And to predict the volt-ampere characteristics of the system,so that the micro-mechanism and macroscopic phenomena are linked to obtain a deeper understanding of the mechanism of electrochemical process1.Study of the Oxygen Evolution Reaction(OER)on the Surface of Transition Metal Oxide with Oxygen vacanciesThe adsorption energy of various oxygen species on the surface of TiO2(110)containing different number of unsaturated Ti atoms(oxygen vacancy)was calculated with DFT.The path of oxygen evolution reaction(OER)is determined,and the volcanic relationship with OER overpotential and adsorption energy is established.The results indicate that the increase number of unsaturated Ti atoms enhances the adsorption of oxygen-containing intermediates on the surface,making the adsorption energy of the intermediates close to each other and the OER overpotential reduced.Based on the electronic structure analysis,we find that increasing the number of unsaturated Ti results a smaller the energy difference of Ti 3d and O 2p orbitals and a lower energy of bonding orbital,and makes the absorption of intermediates on the surface stronger.2.Monte Carlo Simulation of H Adsorption on Pt(111)SurfaceCombined with DFT calculation and CE force field method,Monte Carlo was used to simulate the adsorption of H on Pt(111)surface,and the chemical adsorption isotherm(adsorption free energy and configuration entropy)are obtained.An electrochemical adsorption model containing effects of potential,pH and other effects was established.Based on this model,combined with the experimental adsorption isotherms of chemical adsorption isotherms and underpotential deposition(UPD)regions obtained by MC simulation,the electrochemical adsorption isotherms of overpotential deposition(OPD)regions and the zero charge potential values which consists with the experimental results are obtained.The results show that H will continue to adsorb on the Pt(111)surface in the OPD region and reach the full cover at-0.2V(vs RHE),and the adsorption hydrogen(OPD-H)in the OPD region and the adsorbed hydrogen in the UPD region(UPD-H)are the same type of adsorption hydrogen,i.e.FCC adsorption hydrogen.3.Monte Carlo Simulation of Behavior of Li in LixFePO4Based on DFT calculation and CE method,the forcefield of Li interaction in LixFePO4 was constructed.Using CE forcefield,the equilibrium distribution behavior of Li in LixFePO4 was studied by MC simulation.By analyzing the relationship between the system energy and the distribution of Li(configuration),it is found that the lower the energy of the system when the configuration of Li distribution is closer to the two?phase(lithium-poor phase and lithium-rich phase)structure,the reason is the retained attraction between Li in LixFePO4.At room temperature,the structure of LixFePO4 is mainly concentrated in the vicinity of low energy state(i.e.,phase configuration),which is consist with the observed phenomena.With the increase of the system temperature,the tendency of the structure entropy increases and the tendency of Li to converge weakens,finally LixFePO4 transforms into a solid solution.The equilibrium charge and discharge potential of LixFePO4 under different Li contents is calculated,i.e.the charge and discharge curve at very low rate,and compared with the experimental results.