Influence of humidified synthetic air feeding conditions on the stoichiometry of (La1-xSrx)(y)CoO3-delta and La0.6Sr0.4Co0.2Fe0.8O3-delta cathodes under applied potential measured by electrochemical in situ high-temperature XRD method

摘要

The solid oxide fuel cell symmetrical cells with porous (La1-x Sr (x) ) (y) CoO3-delta and La0.6Sr0.4Co0.2Fe0.8O3-delta electrodes for intermediate temperature applications have been studied under electrochemical polarization and synthetic air + H2O vapor (so called moisturized cathode gas) feeding conditions using high-temperature electrochemical in situ X-ray diffraction method, chronoamperometry, cyclic voltammetry, and impedance spectroscopy methods. Changes in the lattice parameters and electrochemical activity of La0.6Sr0.4CoO3-delta , (La0.6Sr0.4)(1.01)CoO3-delta , (La0.6Sr0.4)(0.99)CoO3-delta and La0.6Sr0.4Co0.2Fe0.8O3-delta were calculated depending on the temperature (T), electrode potential (E), and oxygen partial pressure (p (O2)) applied. Influence of H2O vapor in synthetic air on (La1-x Sr (x) ) (y) CoO3-delta parameters was irreversible and continued expansion of (La1-x Sr (x) ) (y) CoO3-delta lattice observed in H2O vapor + synthetic air feeding conditions has been observed continuously after changing wet cathode gas to dry oxygen. Nearly, reversible behavior of La0.6Sr0.4Co0.2Fe0.8O3-delta lattice has been established and for La0.6Sr0.4Co0.2Fe0.8O3-delta, the cell volume and polarization resistance started to decrease after changing humidified synthetic air to dry synthetic air in the cathode compartment. For the slightly cationic deficient (La0.6Sr0.4)(0.99)CoO3-delta , the cathode structure is more stable and the electroreduction of the oxygen was faster. Detailed comparison of experimental data demonstrates that the dependence of the crystallographic parameters on the electrode potential and temperature applied is in a good agreement with the electrochemical impedance spectroscopy data, indicating that the electrocatalytic activity of the cathode decreases with the rise of Fe ion concentration in B-position of LSCF cathode.