Controlling the internal pressure drops of a kW-scale solid oxide electrolysis cell stack for the uniformity of flow distribution and reaction environment

Abstract

Solid oxide electrolysis cell (SOEC) is gaining attention as a next-generation green hydrogen production technology due to its high hydrogen production efficiency enabled by high-temperature operation. However, the electrochemical reaction characteristics of SOEC exhibit sensitivity to various factors such as flow distribution and steam conversion rate, making it challenging to ensure operational stability due to its high reactivity even at harsh conditions. This study focuses on characterizing the inter-layer flow distribution of a 5 kW-commercial scale SOEC stack, and analyzes the resulting changes in internal temperature, velocity, and chemical composition to understand their impact on inter-layer electrochemical reactions. To investigate this, a high-fidelity threedimensional multiphysics model is developed that accurately simulates stack internal fluid dynamics, thermodynamics, and electrochemistry. The developed model undergoes experimental validations at a stack level to ensure model reliability. Computational analysis results reveal that as the stack height increases beyond 40 layers, pressure drops in the riser and exhaust channels lead to uneven fuel distribution between stack layers. This results in increased inter-layer flow rate deviation and steam mole fraction depletion at higher layers, compromising operational stability. To address these challenges while maintaining stack design geometry, we opt to decrease the permeability of the fuel electrode current collecting layer to increase flow channel pressure drops and achieve uniform inter-layer fuel distribution. Using optimized current collectors for stack-scale operations, flow uniformity significantly improves compared to a reference stack, achieving highly uniform flow distribution. With improved inter-layer flow distribution, all of internal temperature, chemical composition, reaction distribution, and voltage distribution within the stack are uniformly regulated, effectively mitigating fuel depletion issues at the 40-layer outlet. Moreover, design guide map was introduced, providing a structured approach to optimizing current collecting layer permeability. The methodology was applied to an 80 layer stack, demonstrating improvements in flow uniformity and operational stability. This research provides a physical understanding of internal distribution of SOEC during operation and presents a scalable and practical strategy for SOEC stack optimization, offering innovative guidelines for improving fuel distribution through CCL permeability control without altering the stack geometry.