Impedance analysis of a micro tubular solid oxide fuel cell (1^st report, separate analysis of the impedances of the anode and cathode)

A separate analysis of the anode and cathode impedances of a practical solid oxide fuel cell (SOFC) has been performed. Electrochemical impedance spectroscopy is used for the analysis of a micro tubular SOFC havig anode-supported electrolyte with two-electrode set-up. This cell is composed of an Ni/(Zr0₂)_0.9(Y₂0₃)_0.1 cermet anode, an La_0.8Sr_0.2Ga_0.8Mg _0.20_2.6 electrolyte, and an La_0.6Sr _0.4(Co_0.2Fe_0.8)O₃ cathode. Measurements are carried out for the cell operated at 700°C with varying flow rate and composition of H₂-N₂ mixture gas fed into the anode and those of air-0₂ mixture gas fed into the cathode. The anode and cathode impedances are thereby found to appear in low and high frequency regions, respectively. A common equivalent circuit model is applied for the complex nonlinear least squares curve fitting of impedance spectra to acquire the resistances and capacitances of the charge and mass transfers at the anode and cathode, and the cell Ohmic resistance. Then variation of those parameters of the equivalent circuit in accordance with anode gas feed conditions are obtained for the practical SOFC. They are useful parameters for health diagnosis of SOFCs.