Detailed characterization of anode-supported SOFCs by impedance spectroscopy

Anode-supported thin electrolyte cells are studied by electrochemical impedance spectroscopy (EIS). The aim is to describe how the losses of this type of cells are distributed at low current density (around open-circuit voltage) as a function of temperature. An equivalent circuit consisting of an inductance, a serial resistance (R-s), and five arcs to describe the polarization resistance is suggested.

This equivalent circuit is based on previous studies of single electrodes in three-electrode and two-electrode symmetric cell setups. The equivalent circuit components have been assigned to the electrode processes, and the assignments were verified by extensive full cell studies in which the partial pressure of reactant gases on both the electrodes as well as temperature was systematically varied with the aim to identify frequency regions which are dominated by an electrode specific process.

Furthermore, the model is applied on a good performing cell with area specific resistance (ASR)=0.15 Omega cm(2) at 850 degrees C and a poor performing cell with ASR=0.29 Omega cm(2) at the same temperature. Both cells were fabricated using nominally the same procedure. The EIS analysis indicated that the difference in performance originates from microstructural differences on the cathode.

This is further supported by the observation of large differences in the cathode microstructure by scanning electron microscope.