Numerical Modeling And Simulation Of Triple Phase Boundary Of Limiting Current Oxygen Sensor

Oxygen sensors,as specialized sensors for detecting oxygen concentration,are widely used in automotive and aerospace applications.Due to the benefits of having no reference gas,rapid response time,long service life,and excellent testing accuracy,limiting current oxygen sensors have come to be the focus of research and development from academia and industry.The triple phase boundary consisting of pore/solid electrolyte/electrode is the site of electrochemical reactions in oxygen sensors and plays a crucial role in the performance of the sensors.To this end,this thesis takes the triple phase boundary of the limiting current oxygen sensor as the research object to study how it evolves during its long-term operation under high temperature conditions,aiming to provide a reference for sensor design and fabrication.Firstly,the limiting current oxygen sensor’s working mechanism and electrochemical reaction process were analyzed,and a theoretical model describing the electrochemical reaction process at the oxygen sensor’s triple phase boundary was established.Through the analysis of the reaction principle,oxygen diffusion mechanism,solid electrolyte conductivity mechanism and limiting current generation mechanism of the limiting current oxygen sensor,the influence of the triple phase boundary length and its structure on the performance of the oxygen sensor is clarified.Secondly,numerical modeling and simulation analysis of the three-dimensional fine structure of the triple phase boundary were carried out.Based on the electron microscope scans of the sample electrodes,a three-dimensional solid fine structure was constructed after image processing,and a representative volume cell model was selected and a threedimensional fine structure of the triple phase boundary was established.Based on the established structural thermodynamic model and electrochemical model,electro-thermal multi-physical field coupling simulation and electrochemical analysis of the triple phase boundary were carried out.The simulation results show that the average temperature,maximum stress and maximum total deformation of the triple phase boundary increase with the increase of voltage;the electrochemical simulation results verify the established theoretical model.Finally,the simulation analysis of the degradation of the triple phase boundary of the oxygen sensor was carried out.Based on the analysis of the reaction mechanism of the triple phase boundary,it is clarified that material property degradation,material mismatch and creep effect are the main factors affecting the stability of the triple phase boundary,and the simulation of the degradation of the triple phase boundary is further carried out using the finite element method.The simulation results show that: material degradation leads to the drift of the working temperature of the triple phase boundary and the drift increases with the increase of the working time;the length of the triple phase boundary per unit volume increases with the increase of the working temperature and decreases with the increase of the working time;the selection of 8YSZ as the solid electrolyte can enhance the stability of the interface in the triple phase boundary;the creep effect gradually decreases with the accumulation of time and the maximum deformation variable increases with the increase of the creep time.The creep effect gradually decreases with time,the maximum deformation increases with the growth of creep time,and the triple phase boundary length per unit volume gradually decreases with the prolongation of creep time.