Oxide ion transport in promising cobaltites for SOC

Two cobaltites were studied as air electrodes for Solid Oxide Cells with a Cerium Gadolinium Oxide electrolyte (CGO): Ca₃Co₄O_9+δ well known for its thermoelectric properties, and Ba₂Co₉O₁₄. After optimisation of composition and thickness, a very good ASR of only 0.08 Ωcm² was obtained for the 50 wt% Ba₂Co₉O₁₄ - 50 wt% 50CGO composite. In contrast, a value of 0.5 Ωcm² was reached for the 50 wt% Ca₃Co₄O_9+δ- 50 wt% CGO composite. Although, Ba₂Co₉O₁₄ sample contained 18O after annealing, oxide ion diffusion in this compound still has to be confirmed. In contrast, high surface exchange kinetics were measured for both Ca₃Co₄O_9+δ and NdBaCo₂O_5+δ, for which mainly calcium and barium/neodymium were evidenced at the uppermost surface of the samples, whose atoms may play a key role in the mechanism of oxygen molecules dissociation.