Analysis of the Cathode Electrical Contact in SOFC Stacks

The cathode contact layer is a critical component in solid oxide fuel cell stacks and one possible cause of degradation. Even though this layer and its interfaces are responsible for a large proportion of the ohmic resistance, it is generally difficult to identify the degradation without carrying out an autopsy of the stack. As a non-destructive method, electrochemical impedance spectroscopy is used in this work to investigate in-depth the cathode contact and its evolution with the support of distribution of relaxation time and differences in impedance spectra analyses between 650°C and 800°C. By purposefully building a stack with a reduced cathode contact area, the electrochemical resistance of the contact is evaluated and its frequency response identified. Through measurements at various operating conditions the different peaks of the distribution of relaxation time analysis are identified and related to physical phenomena within the cell. These findings are then applied to a stack with a standard contact area in order to explain the degradation behavior observed upon dismounting from the test bench