An analytical approach for solid oxide cell electrode geometric design

Abstract

An analytical model for gas distributions in porous solid oxide cell electrodes is applied to develop dimensionless metrics that describe electrode performance. These metrics include two forms of a dimensionless reactant depletion current density and a geometry sensitive Damköhler number used to assess electrode catalytic effectiveness. The first dimensionless depletion current density defines when reducing electrode thickness no longer benefits mass transfer performance for a given cell geometry. The second dimensionless depletion current density provides a gage of deviation from the limiting current behavior predicted using button-cell experimental and modeling approaches. The Damköhler number and related catalytic effectiveness quantify two-dimensional transport effects under non-depleted operating conditions, providing a means of generalizing insights from reactant depletion behavior for typical cell operating conditions. A finite element solution for gas transport based on the dusty-gas model is used as a benchmark for the analytical model and dimensionless metrics. Estimates of concentration polarization based on analytical and numerical models compare well to published experimental data. Analytical performance predictions provide clear demonstration of the influence of two-dimensional electrode geometry on solid oxide cell performance. These results agree with finite element predictions and suggest that reduction of electrode thickness does not exclusively benefit cell performance.