Optimization of electrolyte and cathode thickness for solid oxide electrolysis cells considering residual stresses and thermal–electrical–chemical–mechanical coupling-induced stresses

Solid oxide electrolysis cells (SOECs) present a promising high-temperature electrochemical technology for efficient hydrogen production and play a critical role in sustainable energy storage. However, optimizing the electrode and electrolyte thicknesses remains challenging due to the competing effects among energy efficiency, current leakage, and mechanical reliability. This study develops an optimization framework coupled with security constraint models for residual stresses during manufacturing and stresses induced by thermal–electrical–chemical–mechanical coupling during operation, to determine the optimal cathode and electrolyte thicknesses for yttria-stabilized zirconia (YSZ) and gadolinium-doped ceria (GDC) SOECs under both constant and variable power input scenarios. The model integrates: (i) an electrochemical framework accounting for current leakage to predict energy efficiency, (ii) residual stress evaluation during manufacturing, and (iii) thermo–electro–chemical–mechanical coupling-induced stress analysis during operation. Two complementary optimization algorithms, sequential quadratic programming (SQP) and particle swarm optimization (PSO), were employed to determine cathode and electrolyte thickness combinations that maximize energy efficiency while satisfying stress safety constraints. The results reveal that optimal electrolyte thicknesses lie in the range 9.04 μm to 22.65 μm for YSZ-Cell and between 70.69 μm to 96.96 μm for GDC-Cell under constant power input, with corresponding cathode thicknesses from 195.24 μm to 500.99 μm and 202.67 μm to 283.74 μm. Regional analyses under variable power input, reflecting differences in solar energy availability, demonstrate that the optimized electrolyte and cathode thicknesses significantly enhance both annual hydrogen production and overall energy efficiency. Specifically, compared with empirical baseline (electrolyte thickness δe,exp=50 μm, cathode thickness δc,exp=500 μm), the optimized configurations improve the maximum energy efficiency by up to 9.54 % for the YSZ cell and 19.20 % for the GDC cell. These findings quantitatively demonstrate that optimizing electrolyte and cathode thicknesses provides a more comprehensive perspective by balancing efficiency and structural safety, offering actionable design guidelines for region-specific renewable hydrogen production systems.