Quantitative contribution of cells and interfaces to SOEC stack performance
image: Experimental diagram
Credit: Xiaolong Wang, Beibei Han, Junkang Sang, Anqi Wu, Yafei Tang, Jianxin Wang，Wanbing Guan.
Solid Oxide Electrolysis Cells (SOECs) represent an efficient and environmentally friendly high-temperature hydrogen production technology, holding significant application potential in the realm of renewable energy storage. However, the performance degradation of SOEC stacks during prolonged operation has been a critical bottleneck hindering their large-scale application. Previous studies have identified the contact between the cell body and the interface as a core factor affecting stability, yet the quantitative contributions of both to stack performance degradation and the underlying mechanisms remain unclear, particularly due to a lack of systematic analysis of the degradation pathways of different components.
This study, conducted by Dr. Beibei Han from the Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, in collaboration with Ningbo University and Zhejiang H2-Bank Technology Co., Ltd., employs a "segmented voltage monitoring method," which integrates voltage leads into three series batteries within the SOEC stack, enabling the quantitative separation of degradation contributions from the cell body and the interconnect-cell interface, thereby providing direct experimental evidence for optimizing stack design. The paper was published in Frontiers in Energy.
The researchers focused on a flat-tube SOEC stack, conducting a 900-hour stability test at 750 ℃, 500 mA/cm² current density, and 60% steam atmosphere. Results showed that the total electrolysis voltage of the stack increased by 0.213 V, corresponding to a degradation rate of 0.93%/100 h. In contrast, the voltage of the three series batteries collectively increased by 0.268 V, while the interconnect-cell interface voltage decreased by 0.055 V, offsetting 25.82% of the total degradation.
Further analysis indicated that battery degradation primarily stemmed from the reconstruction of the three-phase boundary (TPB) and changes in porosity of the Ni-YSZ electrodes, leading to increases in both ohmic resistance and polarization resistance. Among the series batteries, the middle cell exhibited the most significant degradation (1.5%/100 h) due to uneven gas flow distribution. The improvement in interface performance was attributed to the optimization of contact between the interconnect and the electrode during prolonged operation, with the reduction in contact resistance likely related to the growth of oxide layers and the interfacial adhesion under constant pressure.
This study clarifies the quantitative relationship between "cell-dominated degradation and interface-suppressing degradation" within SOEC stacks, providing targets for targeted optimization: on one hand, enhancing cell stability through microstructural control of the electrodes; on the other hand, further leveraging the buffering effect of the interface against degradation through interface contact design. The findings offer critical scientific evidence for the long-term stable operation of SOEC stacks and provide insights for performance optimization in other electrochemical energy conversion devices. In the future, the team will further explore the impacts of thermal cycling and current fluctuations on stack degradation under practical operating conditions.