Exploring the parametric and electrolyte-dependent behavior of SOEC for syngas production via CO2/H2O electrolysis: A 3D multi-physics study

• A 3D multi-physics SOEC model was developed to study CO 2 /H 2 O co-electrolysis under varying operating conditions. • ScSZ-based SOECs showed consistently higher current density than YSZ. • Increasing reactant temperature from 973 to 1123 K significantly increased the current density of ScSZ-based cell. • Flow rate variation affected product mole fractions but had negligible impact on total syngas flux. • Steam-rich feeds significantly boosted H 2 production, while CO 2 -rich feeds lowered conversion and heat generation. A three-dimensional multi-inlet solid oxide electrolysis cell (SOEC) model is developed to investigate the co-electrolysis of CO 2 and H 2 O to syngas using YSZ and ScSZ electrolytes. The model integrates fluid flow, multicomponent species transport, electrochemical and chemical reaction kinetics, and detailed thermal effects to quantify the influence of cell voltage, inlet temperature, inlet flow rate, and feed composition on syngas production and cell behavior. The results show that ScSZ performs better than YSZ under all operating conditions, primarily due to its higher oxygen-ion conductivity and lower activation energy for ion transport, which enable faster charge transfer and more efficient electrochemical reactions. When the cell potential increases from 1.1 to 1.5 V, the ScSZ-based cell achieves a 25% higher current density and superior syngas production compared to the YSZ-based cell. Raising the inlet temperature of CO 2 and H 2 O from 973 to 1123 K improves the ScSZ current density by more than 55%, highlighting the strong effect of temperature on ionic transport. Changing the flow rate between 200 and 500 sccm mainly dilutes the product gases but does not significantly change the total syngas output. Adjusting the H 2 O/CO 2 ratio allows effective control of syngas composition, with steam-rich feeds giving the highest H 2 flux (0.0525 mol m -2 s -1 ). Additionally, the effect of thermal gradients on SOEC stability is also examined, which shows that increasing the voltage raises the internal cell temperature, while changes in flow rate and gas composition cause only minor temperature variations, confirming stable thermal behavior within the studied range. This work provides comprehensive insights into the effect of electrolyte selection and operating conditions on SOEC co-electrolysis performance, guiding the design of more efficient and durable systems for sustainable syngas production.