Evaluation of Nb- or Mo-alloyed ferritic stainless steel as SOFC interconnect by using button cells

The Fe–22Cr–0.5Mn ferritic stainless steel alloyed with Nb or with Mo is evaluated in the button cell configuration at 750 °C in terms of degradation in ohmic resistance and cathodic polarization resistance. STS444 and Crofer22 APU are also evaluated for comparison. Each polarization element is separated by equivalent circuit analysis on the electrochemical impedance spectroscopy data. Cr deposition on the button cell cathode is also analyzed both qualitatively by transmission electron microscope and quantitatively by inductively coupled plasma. The Nb- or Mo-alloyed ferritic stainless steel shows comparable performance with Crofer22 APU in terms of the increase rate in ohmic resistance and Cr evaporation rate, even without the addition of reactive element such as La. When the same amount of Cr is deposited on the cathode, the cathode performance deteriorates more at the high Cr evaporation rate than at the low Cr evaporation rate.

► The Nb- or Mo-alloyed ferritic stainless steels are evaluated as SOFC interconnect. ► Button cell and EIS technique are used for the evaluation. ► Each degradation element is successfully separated with equivalent circuit analysis. ► Cr deposition is analyzed quantitatively and correlated with degradation of cathode.