(687d) 3D CFD Model of Electrode-Supported Solid-Oxide Cells for High-Temperature Electrolysis

A three-dimensional computational fluid dynamics (CFD) electrochemical model has been created to assess high-temperature electrolysis performance of an electrode supported Solid Oxide Electrolysis Cell (ES-SOEC). Electrode-supported cells represent some of the highest performing solid oxide fuel cells currently under development. The nickel cermet material, which serves as the anode in the fuel cell mode and the cathode in the electrolysis mode, has relatively high electronic conductivity and is therefore a logical choice for use as the mechanical support layer in electrode-supported cells. In an anode-supported SOFC, the anode is typically 1 ? 1.5 mm in thickness while the electrolyte thickness can be as low as 10 µm. In the fuel-cell mode, steam diffusion away from the functional layer can be readily pressure-driven. In the electrolysis mode, however, it may be preferable to use an oxygen-electrode-supported cell to reduce the concentration overpotential associated with steam diffusion through the thickness of the electrode toward the functional layer. The typical oxygen-side electrode material for the present cells is lanthanum-strontium manganite (LSM) perovskite. Electrode-supported cells are currently being evaluated to determine their performance in the electrolysis mode. This paper will provide 3D CFD results of a computational study of electrode-supported electrolysis cells. The objective of the work is to determine the relative advantages and disadvantages of anode-supported cells versus cathode-supported cells for operation in the electrolysis mode. Computational results will be validated against experimental data obtained with cathode-supported cells.

Mass, momentum, energy, and species conservation and transport are provided via the core features of the commercial CFD code FLUENT. A SOFC module adds the electrochemical reactions and loss mechanisms and computation of the electric field throughout the cell. The FLUENT SOFC user-defined subroutine was modified for this work to allow for operation in the SOEC mode. Model results provide detailed profiles of temperature, Nernst potential, operating potential, activation over-potential, anode-side gas composition, cathode-side gas composition, current density and hydrogen production over a range of stack operating conditions. Predicted mean outlet hydrogen and steam concentrations vary linearly with current density, as expected. Contour plots of local electrolyte temperature, current density, and Nernst potential indicated the effects of heat transfer, endothermic reaction, Ohmic heating, and change in local gas composition.