Contactless external manifold design of a kW-scale solid oxide electrolysis cell stack and analysis of its impact on the internal stack environment

Abstract

A solid oxide electrolysis cell (SOEC) technology emerges as a promising solution for producing environmentally friendly green hydrogen. However, stacking multiple repeating units to maximize hydrogen production introduces significant challenges, particularly non-uniform distribution of reacting gases and temperature across the cell-layers in internal manifold stacks. To address these issues, external manifold stacks are proposed as a potential solution. However, conventional external manifold configuration utilizes a fastening method that directly connects the stack and external manifold to supply reacting gases. This approach often fails to maintain uniform fastening strength due to thermal expansion of the stack, leading to gas leakage and degradation of electrochemical cells. To overcome these limitations, this study proposes a contactless external manifold design that eliminates direct contact between the stack and the external manifold while focusing on a detailed analysis of heat and mass transport characteristics within the stack and the resulting electrochemical distributions. Meanwhile, using the contactless configuration creates not only a flow path entering the stack but also a newly formed bypass outside the stack, with simulation results revealing that excessive air leakage occurs through this bypass. To resolve this issue, a flow resistance circuit is constructed to derive the flow resistance of each airflow path. Based on the calculated flow resistances, a hook-shaped flow resistance structure is introduced to ensure that the desired airflow rate enters the stack. A comparative analysis is conducted among three configurations: an external manifold stack with the hook-shaped resistance structure, an external manifold stack without the resistance structure, and an internal manifold stack. This analysis elucidates the relationships among pressure, species distribution, temperature, and electrochemical distribution for each configuration. The results demonstrate that the external manifold stack with the hook-shaped resistance structure provides the most uniform internal environment for cells. Additionally, an air ratio study is conducted to verify the validity of the proposed external manifold design under various conditions, confirming its applicability across a wide range of operating conditions and the reliability of the flow resistance structure design methodology.