| The solid oxide fuel cell（SOFC）can directly convert chemical energy into electric energy.It has the advantages of all-solid-state,clean,high-efficiency,wide range of fuel applications,and has broad development prospects.The problems of performance decline and life restrict the commercialization of SOFC.This paper studies the SOFC stability of anode-supported electrolyte membrane flat structure.Experiments are carried out using a single cell of Ni-YSZ|YSZ|GDC|LSCF structure to simulate the temperature,current density and fuel gas distribution of the SOFC stack to study the initial stability of the cell,long-term constant current discharge stability,stability under changing operating conditions,and the effect of fuel exhaustion caused by partial failure on the cell,summarize the cell performance degradation and failure rules,and combine the three-electrode impedance Spectral measurement and other characterization techniques to clarify the mechanism of cell performance degradation.The initial stability of cell was studied by changing operating temperature and current density.It is found that the best temperature at the initial stage of cell is700℃,and the best current density is 350 m A·cm-2.Simulated the possible uneven temperature and current density distribution in the actual flat-panel SOFC stack,and studied the stability of the cell under changing operating conditions.It is found that the decline of the cell under variable operating conditions is significantly higher than that under stable operating conditions.The fuel exhaustion experiments were carried out under different discharge modes to simulate the influence of the fuel gas circuit failure in the SOFC stack on the cell performance.The results show that the constant current discharge test used to simulate the fuel shortage of a certain cell unit in a series reactor will directly damage the cell.The 0.7 V constant voltage discharge mode used to simulate the local fuel shortage of the flat panel cell unit has little impact on the performance of the cell.When the hydrogen depletion occurs during constant current discharge,the discharge current will cause oxygen ions pass through the electrolyte to reach the anode and release oxygen,causing Ni to be oxidized,which expands the volume of the anode and causes the electrolyte membrane to be in a state of tensile stress.Under the action,cracks are generated in the electrolyte membrane to damage the cell.By dividing the cathode and forming the parameter electrode on the air side,the impedance spectrum of the cathode and anode was tested by the three-electrode method.This method is used to study the influence of the hold process during the constant current discharge on the cell performance.It is found that long-term hold will lead to the precipitation of Sr at the cathode and the rapid degradation of cell performance,which will slow down when the cathode is under low oxygen partial pressure.The hold process reduces the electrons obtained by the cathode,increases the valence states of Fe and Co and shrinks the crystal lattice,resulting in the precipitation of Sr and the decrease of the catalytic activity of the cathode.The study also found that the Si element in the cell silicon rubber plug will be deposited on the cell anode due to heat volatilization,but it has little effect on the cell performance.The cell was subjected to a constant current discharge test for 1500 h at a current density of 233 m A cm-2to evaluate its long-term stability and characterize the components of the cell.It was found that the cell declined not significant in the thousand hours,and the decline rately of the voltage only 0.015 m V·h-1.This is demonstrated that the cell with this Ni-YSZ anode-supported structure had good long-term stability and the life is more than 1500 h.After operation,the cell pack was intact,and the silver wire used only as the cathode lead was roughened due to the deposition of impurity elements. |
PDF Full Text Request