Performance Evolution of Ni-YSZ Anode-Supported SOFCs During Initial-Stage Operation

Abstract

Solid oxide fuel cell (SOFC) is a clean and efficient power generation device, which has been widely used in recent years. However, its operation lifetime still needs to be improved to meet the requirements of further commercialization. The performance degradation of SOFCs is affected by many factors. It is meaningful to distinguish these factors and determine the dominant factor(s) for extending the operation lifetime. In this work, the initial operation stage (<100 h) of Ni-YSZ anode-supported SOFCs is mainly focused, since it has been found that the electrochemical performance changes most significantly in this stage. The electrochemical impedance spectroscopy (EIS) is continuously monitored during the operation of cells. Different electrode processes are distinguished through coupled distribution of relaxation time (DRT) and equivalent circuit model (ECM) analysis. Accordingly, the changes of different electrode processes in the initial-stage operation are obtained by detailed comparative analysis of EIS. It’s found that SOFCs go through activation stage and aging stage in turn: i) In the activation stage, the residual NiO in the anode is further reduced, so the porosity of the anode increases and the gas phase diffusion is enhanced, resulting in the performance improvement of the cell. ii) In the aging stage, the Ni particles in the anode agglomerate, so the effective three phase boundary (TPB) density decreases, which leads to the degradation of anode interface reactions and the drop of cell performance. Besides, we speculate that the dominant degradation mechanism in long-term operation (>100 h) is the continuous increase of the anode interface reaction-related resistance, which is mainly caused by gradual agglomeration of Ni particles. This evolution mechanism of electrochemical performance is then confirmed by detailed microstructure characterization. Figure 1