E. Capoen

Characterisation of the electrode-electrolyte BIMEVOX system for oxygen separation. Part I. In situ synchrotron study

Abstract BIMEVOX membranes for electrochemical oxygen separation were characterised under operating conditions using X-ray synchrotron radiation. Three compositions were studied: a slightly Bi-enriched non-doped phase, BIBIVOX.02, a BICOVOX and a BICUVOX phase. Both anodic and cathodic behaviours were investigated at 620 °C for current densities up to 1 A/cm 2 . These experiments demonstrated the self-ability of these electrolytes to dynamically transform into electrode materials under polarisation. This transformation is due to a slight reduction of the material under bias. The transformation is reversible. The initial phase was recovered when the current was turned off. Even low current densities were sufficient to induce this electrolyte–electrode adaptation.

Oxygen transport kinetics of the misfit layered oxide Ca3Co4O9+d

The oxygen transport kinetics of the misfit-layered cobaltite, Ca3Co4O9+δ, known for its thermoelectric properties, was investigated by combined application of 18O/16O isotope exchange and electrical conductivity relaxation techniques. Although oxygen diffusion is found to be two orders of magnitude lower than in well-investigated lanthanum nickelates, e.g., La2NiO4+δ, the mixed ionic–electronic conductor Ca3Co4O9+δ is found to exhibit fast surface exchange kinetics (k* = 1.6 × 10−7 cm s−1 at 700 °C to be compared to 1.3 × 10−7 cm s−1 for the nickelate), rendering it a promising electrode for application as an air electrode in solid oxide cells. In parallel, the chemical nature of the outermost surface of Ca3Co4O9+δ was characterized by means of Low Energy Ion Scattering (LEIS) spectroscopy. The absence of cobalt at the samples outermost surface suggests that the Ca2CoO3−δ rock salt layers in the structure may play a key role in the oxygen exchange mechanism.