Spatial Distribution of Electrochemical Performance in a Planar Segmented SOFC

Spatially inhomogeneous distributions of current density and temperature in solid oxide fuel cells (SOFC) can contribute significantly to accelerated electrode degradation, thermomechanical stresses, and reduced efficiency. This is particularly the case under technically relevant operating conditions, that is, high fuel utilization. A combined experimental and modeling study of the spatial distribution of the electrochemical performance in a planar SOFC was performed in order to determine local effects and to identify critical operating conditions. A planar anode-supported SOFC single cell was locally characterized in a 4×4-segmented cell arrangement. The tests were performed in counter flow operation for various H2/H2O/N2 mixtures at the anode and O2/N2 mixtures at the cathode. Local and global current-voltage relationships were measured in dependence of gas composition and fuel utilization. A two-dimensional elementary kinetic electrochemical model representing the segmented cell along the flow path and through the thickness of membrane-electrode assembly and interconnector was established. It reflects the experimental setup in a highly detailed way and allows to quantitatively interpret experimental observations. The model was validated by comparison to experiments under a wide range of operating conditions. When the cell was operated at high fuel utilization, both measurements and simulations show a strong variation of the electrochemical performance along the flow path. The simulations predict a considerable gradient of gas-phase concentrations along the fuel channel and through the thickness of the porous anode, while the gradients are lower at the cathode side. It is expected that the anode is more susceptible to spatially inhomogeneous degradation than the cathode.