Three-dimensional multiphysics coupling numerical simulation of a proton conductor solid oxide fuel cell based on multi-defect transport

Abstract

The conductivity of the electrolyte of a proton conductor solid oxide fuel cell is not only related to temperature, but also related to the humidity and oxygen partial pressure of the cathode and anode. The gas partial pressure and temperature of the cell have significant inhomogeneity in three-dimensional space, so it is extremely important to develop a multi-field coupled three-dimensional model to explore the electrochemical performance of the cell. In this study, a model is constructed that takes into account macroscopic heat and mass transfer, microscopic defect transport, and the reaction kinetics of defects. The results show that for thin cathodes, the ribs significantly affect the oxygen partial pressure and the concentration of defects on the cathode side. On both sides of the electrolyte membrane, the concentration of hydroxide ions increases with increasing gas humidity. The hydroxide ion concentration increases along the flow direction, but the concentration of O-site small polarons increases on the anode side and decreases on the cathode side. The conductivity of hydroxide ions is more sensitive to the humidity of the anode side, while the conductivity of O-site small polarons is more sensitive to the humidity of the cathode side. Increasing the humidity of the cathode side results in a significant decrease in the conductivity of the O-site small polarons. The contribution of the conductivity of oxygen vacancies to the total conductivity is negligible. The total conductivity on the cathode side is greater than that on the anode side; it is dominated by hydroxide ions on the anode side, and co-dominated by hydroxide ions and O-site small polarons on the cathode side. Increasing temperature significantly increases both partial and total conductivity. When hydrogen depletion occurs, the partial conductivities and the total conductivity exhibit a sharp increase downstream of the cell.