Computational Method For The Constant-potential Free Energy And Its Application In Electrochemistry

Electrochemical catalysis is one of the important probable ways to realize energy storage and conversion,which is essential for establishing a green ecology and pro-moting sustainable development.The experimental and theoretical research in electro-chemistry have achieved great progress in recent years,constantly enriching our un-derstanding of the microscopic mechanism of the electrocatalytic process,and serving as an effective basis for rational design of the electrocatalytic materials.When devel-oping the electrochemical simulation methods at the level of quantum chemistry,the most challenging problem is to accurately construct the relation between the constant-potential activation free energy and the electric potential for each elementary step.This thesis focuses on the development of an efficient and general simulation scheme,that can be employed to study the microscopic mechanism of complex electrochemical pro-cesses.The main work of this thesis is summarized as follows,1.Based on the implicit solvent model and density functional theory,we proposed an efficient and general theoretical scheme of calculating the constant-potential acti- vation free energy.Different amounts of charges were introduced into the system to model the varying potential biases,while a quadratic function was adopted for each critical species to fit the grand canonical free energy versus the potential.The advantage of this scheme is that the constant-potential activation free energy can be easily determined for a wide range of electric potentials,at the cost of a few constant-electrons computations.2.This scheme was applied to characterize the potential effect on the complete reaction pathways of CO₂reduction to CO and HCOO^–on the Cu（211）surface,and the free energy landscapes at different electrode potentials were constructed.It is found that the large reductive desorption free energies of OH^–and HCOO^–are suggested as the origin of the high overpotentials for CO₂reduction.3.With the computational potential-related free energy profiles,we built up the inter-facial reaction–in-electrolyte particle transport model to obtain the current-voltage curves,which is expected to bridge the theoretical simulation and experimental characterization of the kinetics in electrochemical process.This theoretical pro-tocol was applied to simulate the HER/HOR polarization curves on Pt（111）in the full p H range,showing good agreement with the experimental results and verifying the effectiveness of the theoretical model.Through intensive study of the simu-lated polarization curves,the kinetics in alkaline media is suggested as determined jointly by Tafel and Volmer steps,while is solely controlled by the Tafel step in the acidic mechanism.According to the relationship between the electric potential and reaction activity of the intermediate OH*,it is also found that the binding strength of OH*is unlikely an effective descriptor of the alkaline HOR activity.4.In view of the disadvantages of the existing electrochemical theoretical methods,a new simulation method based on the explicit solvation model is in urgent need of development.In order to maintain the near-constant potential condition in estab-lishing a statistical ensemble of the reaction routes,it is necessary to perform a long time-scale molecular dynamics simulation with a large supercell model.We initiate this project by constructing the potential energy surface of the pure water based on the atomic neural network trained with metadynamics simulation,focusing on char-acterizing the equilibrium structure of the bulk water,as well as its self-ionization process.With the unit cell containing 512 water molecules,our calculations quanti-tatively reproduced the O–O radical distribution function and,accordingly,the dif-fusion coefficient.Metadynamics simulation also reveals that the hydrated proton transfers mainly through the single jump mechanism on leaving from the hydrated OH^–.