LSCF materials with different stoichiometry's (variable cobalt and iron contents) have been synthesized and analyzed regarding their phase purity and microstructure. Anode supported SOFCs were manufactured with these LSCF compositions and characterized by electrochemical measuring techniques (DC/AC measurements). Here, we mainly focus on impedance spectroscopy in a broad range of different operating conditions (e.g. temperature, current density, and humidity on the air side) in presence and absence of a suitable chromium source.
Electrochemical impedance measurements performed at 900 °C and a cell voltage of 0.7 V in dry and humid air conditions (Figure 1) reveal that besides an initial formation step (I in Fig. 1) the ohmic and polarization resistances only show small deviations in absence of a chrome source (Rohm: dry ~ 0.125 Ω*cm², humid 0.127 ‑ 0.130 Ω*cm²; Rpol: dry ~ 0.045 Ω*cm², humid 0.047 Ω*cm²; see Fig. 1). During a step-wise increase of current density, i.e. cathode polarization, over 48 hour periods both Rohm and Rpol remained stable (see Fig. 1).
Besides the above mentioned 4-point measurements on full cells, 3-point measurements with a reference electrode were performed on symmetrical electrolyte supported half cells. By this means contributions from the Ni/YSZ anode to the overall cell impedance can be excluded and the individual cathode contributions investigated in more detail.
In combination, both measuring setups should enable detailed information about the individual resistance contributions of the synthesized cathode materials with respect to the operating conditions.
References
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