Numerical simulation of steam electrolysis with a solid oxide cell for proper evaluation of cell performances

A quasi-1D simulation model was developed to estimate total area-specific resistance for overvoltages (Rtot) and cell voltage by separating gas conversion impedance (GCI) from overall real-part impedance in high temperature steam electrolysis with a solid oxide cell (SOEC). GCI and Rtot for a square cell was estimated as 0.012-0.011 Ω cm2 and 0.206-0.216 Ω cm2, respectively, at J = 0.0-1.8 A cm−2, 800 °C, and relatively high flow rates. Even though GCI is small compared to Rtot, ignoring the GCI will result in higher simulation errors at J > 0.5 A cm−2. Simulation results attained ±0.3% or better precision against measured cell voltages at 750-850 °C. Furthermore, case studies at 800 °C revealed ±40% local current density distribution in the cell at 1.0 A cm−2 and 82% steam utilization. GCI was roughly inversely proportional to gas flow-rates and depended on steam utilization. Improvement of Rtot to 0.150 Ω cm2 could attain more than 1.75 A cm−2 at 1.30 V.