Study of Hydration/Dehydration Kinetics of SOFC Cathode Material Ba0.5Sr0.5Co0.8Fe0.2O3-δ by Electrical Conductivity Relaxation Technique

In a recent work Grimaud et al. [J. Electrochem. Soc., 159, B683 (2012)] have shown that it is possible to insert water in fast oxygen ion conducting oxide with high oxygen non-stoichiometry, such as Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF5582) and create the possibility of proton conductivity in them. Here we study the hydration/dehydration kinetics of BSCF5582 by electrical conductivity relaxation technique in 500-900°C range. The values of proton diffusivity (D̃iH) and oxygen diffusivity (D̃vH) were extracted by applying the concept of decoupled diffusion of H and O species upon hydration/dehydration, and D̃iH and D̃vH were obtained from the non-linear least square (NLS) fitting of conductivity relaxation data. The decoupled diffusion in BSCF5582 was verified by comparing its conductivity relaxation profile with the simulated conductivity relaxation profiles for proton conducting oxides with different D̃vH/D̃iH ratios. D̃iH of BSCF5582 were comparable with other proton conducting perovskite-type oxides. Similarly, D̃vH values obtained in this work in humid air atmosphere [−2.9≤log(pH2O/atm)≤−2.29] were ∼10−4 cm2s−1 and they were comparable to the D̃chem values obtained in dry air [−0.96≤log(pO2/atm)≤−0.64] in previous report.