Oxygen reduction at the surface and the hetero-interface of La-Sr-Co-O-oxides

To date, we have reported that oxygen surface exchange is enhanced along the hetero-interface consisting of (La,Sr)₂CoO₄ and (La,Sr)CoO₃. However, there still remain questions on the detailed mechanisms. In this study, we examined how the composition of porous (La,Sr)₂CoO₄, fabricated on (La,Sr)CoO₃ film, affects the enhancement. Layered electrodes consisting of porous (La _1-xSr_x)₂CoO_4±δ (x = 1.0 and 0.8) and La_0.6Sr_0.4CoO_3-δ were prepared and tested by impedance spectrometry. Regardless of the La/Sr ratio in (La,Sr)₂CoO₄ phase, the area specific conductivity was modified at lower temperatures and in higher oxygen partial pressures while the degree of the enhancement was independent of La/Sr ratio. La _0.6Sr_0.4CoO_3-δ film electrode degraded. Composition analysis of the film surface suggested that it had precipitates such as Sr- and Co-oxides. On the other hand, when porous (La,Sr) ₂CoO₄ was fabricated on La_0.6Sr _0.4CoO_3-δ,* film, surface precipitates disappeared. This suggested that the (La,Sr)₂CoO₄ phase plays an important role to keep the composition of La_0.6Sr _0.4CoO_3-δ film to be a perovskite structure possibly by accepting and/or releasing cations near the hetero-interface, resulted in the modification of the electrode performance.