Effects Of Irregular Electrode Microstructure Morphology Detail On Multi-physics Performance Of Fuel Cell

As an energy conversion equipment,Solid Oxide Fuel Cell?SOFC?has become a hot spot for various countries to compete in terms of its high efficiency,cleanliness and diverse fuel forms.An extensive concern on SOFC materials and cell fabrication processes has caused the development of kernel components—electrodes,from principle single-phase electrodes,to porous electrodes,composite gradient electrodes and skeleton electrodes,then to the development and application of medium-temperature e^-/O^2-mixed conductive materials and H⁺conductive materials.The performance of SOFC monomer has been greatly improved,and the chemical energy-electric energy conversion power density can reach 1.3 W/cm²,and it is also extended from high temperature?700-1000 ^o C?to medium-low temperature?350-650 ^oC?application areas.In fact,for the different electrode compositions,fabrication methods and processes,the most direct result is the different microstructural features of the electrodes,which in turn affects the macroscopic transmission properties of the composite electrode and the multi-physics cooperative working characteristics.Therefore,it is of great significance to study the influence of electrode structure and microstructure on the performance of multi-physics of fuel cells,and to create a corresponding large-scale engineering analysis technology.1,A multi-physics model which carefully considers detail electrochemical reaction,electric leakage,and e-,ion and gas transporting coupling processes within a typical IT-SOFC button cell is developed and verified.Three-dimensional multi-physics model is established by COSMOL Multiphysics,and the accuracy of the model is verified by comparison with experimental results.Then,the influences of different cathode/anode area ratios A_ca/A_ann on the button cell performances are carefully investigated,while different micro-structure parameters,electrode properties,component thicknesses and exchange current densities of reaction interfaces are varied within reasonable value ranges.To verify the effectiveness of the multi-physics model for further study of the effects of microstructure details on multi-physics processes.2,The influences of different cathode/anode area ratios A_ca/A_ann on the button cell performances are evaluated negligible.It is concluded that the IT-SOFC button cell is based on the radius of the smaller side electrode,and the actual effective area of the excess of the radius of the electrode on the larger side is only 0.03 cm.The influence of the large-area electrode region beyond the radius region on the physical,conductive,electrochemical and other multi-physics properties of the cell is ineffective.It is concluded that at the current button cell scale,the effect of the dimensions effect of the cathode/anode area ratio on the performance of the button cell is negligible.In the subsequent process of studying the influence of microstructure morphology on cell performance through electrode microstructure reconstruction,it is not necessary to consider the influence of cathode/anode area ratio,and only need to meet the minimum size requirement of isotropic.3,Taking the traditional LSCF-SDC composite electrode as an example,the composite electrode has three irregularities:microstructure irregularity,phase distribution non-uniformity?gas phase,LSCF material phase,SDC material phase?,and uneven distribution of properties?such as regional electron,ionic conductivity,thermal conductivity,stomatal distribution?;the traditional direct meshing method further brings the irregularity of mesh morphology.Therefore,it is pointed out that the traditional methods have natural deficiencies in terms of computational power and numerical stability.At the same time,they can only treat single physics field problems,unable to reflect the influence of microstructure details on multi-field cooperative performance,and cannot deal with the situation of new composite cathode with mixed conductance materials.4,In this paper,an innovation method of processing large scale irregular microstructure with regular grid is proposed to solve a series of shortcomings of traditional direct mesh calculation methods.The effectiveness of the method is illustrated and verified by two different composite electrode components,firstly,the irregular microscopic morphology of the composite electrode is reconstructed by random packing of spheres,and the spherical particles are randomly distributed by EDEM.In order to avoid stochastic errors in the construction process,the method of observing the coordination number is adopted.When the spherical particle radius and the size of the model reach a certain ratio,the stacked three-dimensional irregular electrode microstructure does not depend on the specific model size.Based on the irregular microstructure of LSCF/YSZ composite electrode of IT-SOFC button cell,the microstructure of the composite electrode is characterized by a regular grid with irregular feature information,and then imported into the finite element analysis software to calculate the relevant properties.Therefore,the numerical calculation difficulty caused by the irregular structure morphology is solved.Calculated results including effective electronic conductivity,effective ionic conductivity,gas transports,and distribution of percolation TPBs.The method proposed and verified in this chapter provides an innovative method path for the further analysis of the 3D multi-physics numerical analysis of SOFCs by combining 3D irregular microstructure details based on composite electrodes.