Cross-Validation
of the Remarkably High Surface Oxygen
Exchange Kinetics of PrBa0.5Sr0.5Co1.5Fe0.5O5+δ: A Combined Thin-Film Mass
Relaxation and Bulk Electrical Conductivity Relaxation Study
posted on 2024-03-12, 00:13authored byXin Qian, Sossina M. Haile
In this work, we measure the oxygen kinetic properties
of double
perovskite PrBa0.5Sr0.5Co1.5Fe0.5O5+δ (PBSCF), a material widely used as
the air electrode in solid oxide electrochemical cells, by mass relaxation
(MR) and electrical conductivity relaxation (ECR) experiments. MR
studies are carried out using thin films deposited on a gallium phosphate
piezocrystal microbalance, and ECR studies are performed using a bulk
bar sample with 97% theoretical density. Measurements are performed
at 600 °C over the temperature oxygen partial pressure range
from 10–4 to 0.21 atm. Despite the differences in
experimental formats and surface microstructural features, the ks values extracted from the two methods are
found to be in good agreement with one another. The rate constant
is found to increase with oxygen partial pressure with a power law
dependence, rising from 1.0 × 10–6 cm/s at
3.2 × 10–4 atm to 1.2 × 10–4 cm/s at 0.24 atm, as averaged over the oxidation and reduction directions.
The rates in the oxidation direction are observed to be slightly higher
than those in the reduction direction for a given pair of pO2 values, suggesting that the final pO2 value controls the overall relaxation behavior.
The power law exponent describing the dependence of ks on pO2 is found to be 0.74
± 0.01. The ECR study of the bulk sample reveals that even with
a diffusion length of 1.8 mm, the relaxation process is largely free
of diffusion limitations, indicating that PBSCF has the high bulk
transport properties required for a double-phase boundary oxidation/reduction
pathway.