Initial-Stage Performance Evolution of Solid Oxide Fuel Cells Based on Polarization Analysis

Abstract

Solid oxide fuel cell (SOFC) has attracted more and more attention in recent years due to its high efficiency and low pollution. However, lifetime and stability are still limitations that affect further commercial applications of the SOFC technology. Therefore, it is critical to establish an online monitoring and analysis method to study the mechanism of SOFC performance evolution. The initial performance evolution of SOFCs is more apparent and non-linear than the subsequent stages, affecting the performance calibration and trading, especially for the industrial large-size cells and stacks. In this study, a single cell with an effective area of 100 cm2 was tested in Xuzhou HuaTsing Jingkun Energy Co. Ltd. under the constant current condition with humidified H2 for 80 hours after the NiO-YSZ anode was reduced for 4 hours. During the operation, the EIS data under different DC electrical current biases (0, 20, 50, 100, 300 mA cm-2) and j-V curve were recorded at 24-hour intervals. The EIS data were decomposed by the distribution of relaxation time (DRT) method, and the evolution of each electrode process under different polarization conditions was obtained. For the first 22 hours, the voltage under galvanostatic test and the power density at 0.7 V increased. The performance improvement is mainly due to the increase of the OCV and the decrease of the anode gas diffusion as well as gas conversion resistance, which can be attributed to the further anode reduction. The long reduction time is related to the low porosity and fine granularity of the Ni-YSZ anode, which was preliminarily verified by FIB-SEM. During the next 60 hours, the voltage dropped rapidly, and the power density at 0.7 V decreased by 27%. This nonlinear degradation was mainly caused by the weakening of the charge transfer reactions at the anode and the O2 surface exchange kinetics at the cathode. With the increase of current density, the deterioration of anode reaction gradually became the dominant factor for the increase of polarization impedance.