Performance Evaluation of High Current Density (HCD) Solid Oxide Electrolysis Cell (SOEC) Hydrogen Production System in Endothermic Mode: An Energy and Exergy Perspective

Solid oxide electrolysis cell (SOEC) systems operating at high current densities (HCD) are emerging as sustainable and efficient solutions for hydrogen production. However, the performance of the HCD SOEC systems in endothermic mode, which requires significant external energy, is underexplored. Existing studies often lack comprehensive exergy analyses and effective energy management strategies. Accordingly, this study bridges these gaps by developing a 10 kW HCD SOEC system using Aspen HYSYS software and analyzing five different cases with varying fuel composition, external steam utilization, and fuel recirculation. The cases were systematically evaluated using energy and exergy models to assess their potential and operational possibilities in endothermic mode. Simulation results indicated that all designed cases achieved a hydrogen production rate of 0.076 g s⁻¹. Systems without external steam and recirculation exhibited low overall performance. However, integrating external steam and recirculation strategies significantly boosted the overall performance (Case 5 (E-DR)), achieving the highest lower heating value LHV-based overall energy and exergy efficiencies of 78.2% and 77.6%, respectively, making it the best configuration under HCD endothermic conditions. In-depth exergy analysis revealed that the SOEC stack and fuel superheater (FS) units experienced the highest energy dissipation in all cases and presented the highest improvement potential. Additionally, parametric analysis showed that Case 5 (E-DR) outperformed all other designed cases when operating with higher external steam temperature, external steam factor, and a recirculation ratio of 0.5. This case maintained superior performance up to 54% steam utilization. Beyond this point, the external steam-supported system without recirculation (Case 3 (NRE-H)) exhibited superior performance, thus offering a simpler design by eliminating the need for recirculation. Overall, these insights pave the way for the advancements in SOEC technology under HCD endothermic conditions.