Dependence of cell resistivity on electrolyte thickness in solid oxide fuel cells

In solid oxide fuel cells, the measured cell resistance is usually higher than the calculated value based on the electrolyte thickness. Such a phenomenon is called a constriction resistance and can be represented by a cell:electrolyte resistivity ratio, λ = ρcell:ρelectrolyte, where ρcell = Rcell/δ (δ is the electrolyte thickness). As ρelectrolyte is a property of the electrolyte and is not affected by the electrolyte thickness, the change in λ with electrolyte thickness is an indication of the dependence of the constriction effect on the electrolyte thickness. In this study, the relationship between cell resistivity and the thickness of a yttria-stabilized zirconia Y2O3–ZrO2 (YSZ) electrolyte is investigated. The ρcell increases with decrease in electrolyte thickness and can be expressed as follows ρ_cell=A_0exp(E_a/RT)-B_0 δexp(E_b/RT) This empirical relationship is valid when 0 ≤ δ ≤ δ* where δ* is the electrolyte thickness when ρcell = ρelectrolyte (i.e., λ = 1). The constriction effect depends significantly on the electrolyte thickness and the electrocatalytic activities of the electrodes, as well as on the operating temperature. The validity of the relationship is discussed.