Mechanism Of Chromium From Metal Interconnect Poisoning SOFC Cathode Material

Solid oxide fuel cell（SOFC）is a device that directly converts hydrocarbon chemical energy into electrical energy.It does not require a combustion reaction,so it has the advantages of clean and pollution-free,high conversion efficiency,and no noise.However,there are many problems remains to be solved,such as material aging,sulfur poisoning of the anode,and chromium poisoning of the cathode.The poisoning of cathode materials is a problem that seriously affects the long-term stability of SOFC.The methods of electrochemical detection and material analysis have certain limitations,it can only testing physical characteristics such as current and voltage,however,the mechanism of poisoning at the micro level,as well as the relationship between poisoning and thermodynamic properties is difficult to clarify.Therefore,we have constructed a research method combining microscopic material calculation to macroscopic electrochemical test and Multiphysics simulation.The in-depth study of the poisoning characteristics of traditional cathode material LSM has been carried out,revealing the mechanism of fuel cell poisoning.The research content of the thesis is divided into the following points:Firstly,the basic operation theory of SOFC is described.Based on the literature research,the types of SOFC cathode materials are reviewed,and the research progress of SOFC cathode poisoning and the problems to be solved are summarized.Secondly,based on the simulation results of COMSOL Multiphysics,the conductivity of the cathode material before and after sintering of LSM cathode contact with SUS430 stainless steel was tested by design experiment,and the relationship between the detected porosity,applied pressure and the decrease of conductivity caused by cathode poisoning was established.After contact with stainless steel,no Cr elements were detected in the LSM,indicating that it contained very little in the LSM,but still caused a serious drop in the LSM cathode conductivity.In order to simulate the reaction between LSM cathode and Cr in stainless steel,we designed a comparison of different proportions of LSM/Cr₂O₃mixture for sintering experiments and tested the products.In addition,the DFT first-principles calculations on the adsorption and diffusion behavior of LSM crystals were carried out,and the adsorption energy and migration energy of Cr on different crystal planes of LSM were analyzed.Finally,the SOFC half-cell model and the micro-cathode/electrolyte/anode（sandwich）contact model were constructed using COMSOL Multiphysics software.In the half-cell model,we assume that the Cr distribution increases in the direction perpendicular to the cathode toward the electrolyte,so physical parameters such as Young’s modulus（E）,Poisson’s ratio,and thermal expansion coefficient（TEC）,conductivity,etc.also varies along this direction after poisoning,and they are set as a function of Cr distribution,and then coupled with momentum transfer,mass transfer,heat transfer,electron and ion transfer equations to solve the thermal stress distribution.In contrast,in the sandwich microscopic model,we set up the cathode-electrolyte contact layer,and studied the effect of the contact mode change of the contact layer on the thermal stress at the electrolyte and cathode interface,and assumed that the contact layer was completely poisoned after contact.In summary,we combined experimental measurement,first-principles calculation and multi-physics simulation to reveal the mechanism of SOFC cathode poisoning,and predicted the effects of poisoning on thermal stress at the macroscopic and microscopic levels,and studied the contact form of the contact surface.The DFT calculation provide a basis for SOFC material modification and thermal stress analyze gives an operational performance prediction.