Study On Electrochemical Impedance Spectroscopy Model Considering Electric Double Layer Effect

Electrochemical impedance spectroscopy(EIS),with the advantages of in-situ and non-destructive,is widely used in performance monitoring,fault diagnosis and parameter identification of electrochemical energy storage and conversion devices.However,data analysis of EIS is difficult and requires reasonable models.Typical models include equivalent circuit and physical models.Although the equivalent circuit model is widely used to fit experimental data,it cannot consider the internal mechanism of the research system,which is easy to cause overfitting and incorrect analysis of EIS data.Therefore,this thesis mainly studies physical models of EIS,including solving methods of physical EIS models,EIS models of ideally polarizable electrode and chemisorption reaction.The specific research contents and conclusions are as follows.(1)For the solving methods of physical EIS models,this thesis deduces and compares the advantages and disadvantages of analytical solution,the time-domain numerical method,and the frequency-domain numerical method in detail,and distinguish the applicable scenarios of each method.Based on above methods,this thesis develops analytical models for the first-order and second-order EIS of metal deposition reaction considering diffusive mass transfer.The results show that,compared with the first-order impedance,the second-order impedance can effectively consider charge transfer coefficient and can be used as a method to extract the charge transfer coefficient.(2)As the traditional Gouy-Chapman-Stern(GCS)model cannot explain the frequency dispersion of the electric double layer(EDL),this thesis uses the Poisson-Nernst-Planck equations to describe mass transfer,which effectively consider the non-electroneutrality,mass transfer in EDL and the potential drop in the Helmholtz layer,develops an exact analytical impedance model for ideally polarizable electrode at the potential of zero charge(PZC).This model gives a direct theoretical explanation for the frequency dispersion of the EDL capacitance.Based on this model,this thesis reveals the problem of the conventional GCS model violating the basic principle of electrostatics.In addition,the comparison between the numerical solution and the analytical model shows that established analytical model has a good applicability for the case of non-PZC conditions.(3)For the elementary step in electrocatalysis,adsorption,this thesis develops an analytical impedance model for the adsorption reaction,which self-consistently considers the coupling relationship of adsorption reaction,EDL charging and mass transfer,and the lateral interaction of adsorbates.Asymptotic analysis of this model shows that the common Frumkin-MelikGaikazyan model is only applicable to the conditions of a complete singleelectron reaction,a sufficiently thick Nernst diffusion layer and a low enough frequency.The experimental results at different temperatures and voltages were used to verify the model and fit the activation energy of the adsorption reaction.Through simplified analysis of the new model,this thesis gives theoretical explanations for impedance characteristics in different frequency ranges,and reveals why diffusion behavior cannot be observed in experiments.In this thesis,the study on the physical EIS models can be used to fit and analyze the experimental data of metal deposition reaction,ideally polarizable electrode and adsorption reaction,which is helpful for design and optimization of corresponding electrochemical devices.