Oxygen incorporation at the three-phase boundary of LSCF-SDC composite

Oxygen reduction at LSCF-SDC (La0.6Sr0.4Co0.2Fe0.8O3 − δ-Sm0.2Ce0.8O1.9) composite cathode might take place at the LSCF-gas two-phase interface (2 PB) and the LSCF-SDC-gas three-phase boundary (3 PB). A method is developed to determine the oxygen incorporation rate and the amount of incorporated oxygen at 3 PB using the electrical conductivity relaxation technique. The obtained results are powerful supports to the viewpoint that oxygen incorporation at 3 PB is much more facile than that at 2 PB. The amount of oxygen incorporated absolutely at 3 PB plays a dominating role in the total process, which actually contributes an average of more than 70% when only 4.5 vol. % SDC is added to LSCF. The incorporation rate at 3 PB is found to be affected not only by the 3 PB length but also the diffusion of oxygen species on the LSCF surface. An effective surface diffusion length of about 1.5 μm is suggested by the relation between the rate, 3 PB length and LSCF surface area.