Solid oxide cell stack operating parameter optimization considering various stresses

Abstract

In this study, the finite element method is applied to evaluate and optimize operating parameters for large-scale solid oxide cell stacks by involving detailed-structure stress model and homogenized-structure multi-physics computational fluid dynamics model. A proposed one- and two-step temperature gradient evaluation method (combining end-plate unilateral difference and internal-cell central difference) is employed to establish a quantitative relationship between inter-cell temperature gradients and maximum stress, and to define a “safe operating window” criterion. It is found that cell residual stress establishes a preloaded mechanical state and dominates multi-stress coupling affecting the stress distribution in the stack. When further coupled with bolt-preload-induced assembly stress, the compressive stress is amplified in critical regions from 62.92 MPa (the assembly stress alone) to 565.81 MPa, while the stress concentration is intensified on vulnerable areas such as the electrolyte layers. Subsequent coupling with the stack operation-induced thermal stress drives the tensile stress to 700–1000 MPa. This multi-stress coupling narrows the operating window, with critical temperature gradient thresholds identified as 36.4 K·cm⁻¹ and 40.2 K·cm⁻¹ under assembly-thermal coupling, and 21.5 K·cm⁻¹ and 29.1 K·cm⁻¹ when all stresses are included. Guided by the safe threshold of 21.5 K·cm⁻¹, the stack operating parameters are further optimized to balance the trade-off between electrochemical performance and mechanical constraints.