Changes in SOFC Cathode Crystallographic Structure Induced by Temperature, Potential and Oxygen Partial Pressure Studied Using in-Situ HT-XRD

Reversible changes in the lattice parameters of SOFC cathode were observed depending on the temperature (T), electrode potential (E) and oxygen partial pressure (p_O2) applied. At fixed T and p_O2, the cathode potential noticeably influences the unit cell volume, thus, the oxygen stoichiometry and concentration of vacancies.

The stabilization time of the XRD peak was in minute scale similarly with the plateau time on chronoculonometric curves. Relaxation time of the changes in crystal dimensions are correlated with electrochemical measurement data. The electrode structure (porosity) has strong influence to the shift time of XRD peak.

There was registered only slight influence of oxygen partial pressure and potential to the crystallographic parameters of LSM (La_0.6Sr_0.4MnO_3−δ). At the same time for LSC (La_0.6Sr_0.4CoO_3−δ) and GSC (Gd_0.6Sr_0.4CoO_3−δ) the crystallographic unit cell volume was a function of electrode polarization and oxygen partial pressure. There is no remarkable vacancy formation detectable with HT-XRD in LSM cathode lattice caused by electrode polarizations applied.

Thermochemical crystallographic expansivity study of LSM, LSC and GSC cathodes with in situ HT-XRD method gives valuable experimental data about the crystallographic changes caused by changes in operating parameters like cell potential, temperature, and oxygen partial pressure in cathode compartment and therefore helps to understand thermomechanical and degradation behavior as a function of different conditions applied for  SOFC cathode.