Multiscale Modeling Of The Cathodic Reaction In Solid Oxide Fuel Cell

With the rapid development of the economy and the growth of the population,the world's energy consumption is increasing.Simultaneously,the impact of fossil fuels on the environment and the global climate is becoming more and more serious.Confronted with the challenges of energy conservation and environmental protection,we must develop advanced clean energy systems.Solid oxide fuel cell?SOFC?is a new energy technology with high efficiency and environmental protection.It directly converts the chemical energy of fuel into electric energy and thermal energy without combustion.It provides an effective solution to these challenges and has attracted extensive attention and research from domestic and foreign.The polarization loss of cathode is very large in SOFC.In order to build an efficient fuel cell,it is very important to understand the mechanism of cathode oxygen reduction reaction.In this thesis,a multiscale model for studying the cathodic oxygen reduction in solid oxide fuel cells based on La_{0.6 25}S r_{0.3 75}Co_0.25F e_0.75.75 O_3-?andCe_0.95Gd_0.05.05 O_{1.9 5} was established.The main contents of this thesis are as follows:The lattice structure ofLa_{0.6 25}S r_{0.3 75}Co_0.25F e_0.75.75 O_3-?andCe_0.95Gd_0.05.05 O_{1.9 5}is constructed.First-principles method based on density functional theory and generalized gradient approximation was used to calculation the energy barriers for each reaction step of oxygen reduction reaction,which can be separated into oxygen reduction reaction on the LSCF surface,oxide ion transport in the bulk LSCF,the oxide ion exchange at the LSCF/GDC interface.And compare the energy barrier of each sub-step in the process of oxygen reduction reaction under different configurations of crystal structure.According to the transition state theory,the energy barrier calculated by density functional theory is used to calculate the reaction rate constant and the diffusivity in each reaction and transport step of oxygen reduction reaction.The continuum model is carried out.The results of reaction rate constants and diffusivities calculated by the transition state theory are used in the continuum model to calculate the current density-overpotential curves.Compared with the experimental results,it is shown that the results are reliable.Finally,sensitivity analysis is carried out to determine the key steps of oxygen reduction at the cathode by comparing the effects of the corresponding reaction parameters on the current density-overpotential curves.Sensitivity analysis shows that the O-O bond breaking process has a significant impact on the SOFC performance,which is the key step in the reaction.