Effective Properties Theory And Simulation Of Nano-Composite Electrode Of Solid Oxide Fuel Cell

The worldwide demand for the clean and efficient utilization of fossil fuels such as coal, petroleum, natural gas makes the solid oxide fuel cells(SOFCs) which can directly use hydrocarbon fuels as a clean and efficient power generation get more and more attention. Porous electrode is an important part of SOFC, its performance determines the performance of SOFC directly. There are a lot of experimental research on nano-composite electrode due to the high mechanical matching of the electrolyte and the small polarization loss of it. However the theoretical research is lacking hindering its theoretical analysis and modeling activity. The development of the theory for the effective properties of nano-composite electrode and the establishment of the multi-physics model of SOFC with nano-composite electrode is very meaningful for the experiment.This dissertation based on the physical picture of nano-composite electrode and the traditional theory, developed the theory of effective properties for the nano-composite electrode and optimized the microstructure and the composition of the nano-composite electrode. The main content are as follows:In the first chapter, we firstly introduced the development of the fuel cells, secondly we outlined the multi-physics simulation theory, the details about the governing equations are also described, thirdly we described the concept, background, production technology and the research status of nano-composite electrode, in the end we gave a brief introduction of the simulation technology and the theoretical simulation method.In the second chapter, based on the specific geometric structure of the nano-composite electrode and the hard sphere distribution model in traditional conductivity theory, we made the assumption that the electrode is constructed by the random distribution of the homogeneous conductive equivalent balls and developed the conductivity theory for the nano-composite electrode. We also developed the ionic conductivity theory for the triplet nano-composite electrode based on the parallel circuit assumption. These results are further verified by the relevant experimental data.In the third chapter, based on the scaling theory for the percolation threshold of a finite thickness layer, we modified the calculation method of the effective conductivity of the nano-particle shell in the second chapter. We also used this modified theory to explain some unique experiment phenomenon of nano-composite electrode and discussed the results produced by the layer number modification. This modified conductivity theory was further verified by compare our results with the experimental conductivity data vary with different volume fraction of Ni, different temperature and different electrode structure. This conductivity theory can pave the way for the optimization design of nano-composite electrode.In the fourth chapter, we developed the electrochemical reaction theory and the gas transmission theory of nano-composite electrode and got the analytical expressions of the three phase boundary length and the effective pore size of it. We also verified these effective properties with experiment data and optimized the microstructure and the composition of the triplet nano-composite electrode.In the fifth chapter, the theoretical effective properties of our theory are further used in multi-physics modeling which couples the intricate interdependency among ionic conduction,electronic conduction, electrochemical reaction and gas transport. The obtained I-V curves agree with the experiments, verified the accuracy of our property theory. Quantitative comparisons of the different electrode including conventional electrode, single-phase infiltrated electrode and binary-phase infiltrated electrode are also made, given us a chance to get better understanding of the advantages and disadvantages of the different electrodes.The sixth chapter gives a summary of this dissertation.