Insights Into The Physics And Electrochemical Processes Within Large Scale Irregular Microstructure Morphology Based On Porous Composite Electrodes

As the continuous development of solid oxide fuel cell(SOFC)technology,new materials with different functions and complex microstructure designs have been developed and applied,for example,recently developed electrodes usually have complex micro/nano structures.It is generally believed that the microstructure characteristics of porous composite electrodes will have a great impact on the electrochemical efficiency and durability of SOFCs.In this article focuses on composite electrodes composed of mixed conductive materials and pure conductive materials.First,the electrode reconstructed by random packing of particles is applied to study the relationship between microstructure parameters and electrochemical performance.Then a regular grid matrix with irregular chemical and physical property information is used to investigate the effects of different microstructure morphology on the properties of the composite electrode,so as to avoid a series of problems caused by direct meshing and numerical solution of irregular structures.Finally,the model combines the reaction kinetics to study the large-scale microstructure morphology characteristics and the cooperative performance of the electrochemical and multi-physical transport inside the SOFC porous composite electrode.The specific research content is as follows:1.In this thesis,the particle packing based discrete element method is applied to study the correlations between microstructural parameters and electrochemical properties of LSM-LSCF composite electrodes.Firstly,through the verification of domain size independence and the comparison with the percolation theory,the computational domain size and effectiveness of the particle packing are determined.Then,the changes of the electrochemical reaction sites in the composite electrode with the LSM volume fraction under two different ratios of particle radius are investigated,including the percolated LSCF-LSM-pore three-phase boundaries(TPBs)per electrode volume,three-phase boundaries per electrolyte surface,percolated LSCF-pore double phase boundaries(DPBs)and distribution law inside the electrode.2.In this thesis,based on the reconstructed composite electrode,the regular mesh matrix with different properties information is used to overcome the shortcomings of the traditional calculating method is proposed and its validation,accuracy and advantages are tested from different perspectives.Firstly,the physics field calculated by the new method and the traditional finite element method is compared to demonstrate its validation and accuracy.Secondly,the effectiveness of the method and its capabilities in dealing with three dimensional large scale composite medium morphology are proved by calculating effective electronic conductivities within a 40×40×40?m~3LSCF-YSZ composite electrode.Then,taking a typical LSCF-YSZ composite electrode as an example,the distribution details of voltage and current inside the large scale microstructure morphology are obtained,then the effective conductivity at different volume fractions of LSCF is calculated.Finally,its capability in solving the multi-physics coupling processes within a large scale micro morphology structure are also tested and proved by comparing with the experimental result.