Electrochemical Impedance Analysis of SOFC with Transmission Line Model Using Distribution of Relaxation Times (DRT)

In this work, electrochemical impedance spectroscopy (EIS) and distribution of relaxation times (DRT) analysis were used to evaluate the performance determining parameters for a solid-oxide fuel and electrolysis cell. The SOFC/EC was formulated with 8 mol% Yttria-stabilized zirconia (YSZ) electrolyte sandwiched between Ni-YSZ fuel electrode and La0.6Sr0.4Co0.2Fe0.8O3-10mol% gadolinium doped ceria (LSCF6428-GDC10, 5:5) composite air electrode. To deconvolute the multistep elementary reactions at both of the electrodes, EIS was measured as a function of temperature (775 °C-850 °C), gas compositions, and gas flow rates (50-200 sccm). Concurrently, DRT analysis was employed to resolve frequency-dependent electrode reactions effectively. From the DRT analysis, multistep elementary reactions at fuel and air electrode were separated and corresponded to a transmission line equivalent circuit model with parameters ( R s , e l . , R p , e l . a n d C p , e l . ). Finally, the cell performance limiting factors such as apparent diffusivity ( D ˜ a p p ), surface reaction constant ( k ), and effective lengths ( L e f f ) of each electrode were determined.