Evaluation of layered perovskites YBa1−xSrxCo2O5+δ as cathodes for intermediate-temperature solid oxide fuel cells
Résumé
This study is focused on the structural characteristics, oxygen nonstoichiometry, electrical conductivity, electrochemical performance and oxygen reduction mechanism of YBa1−xSrxCo2O5+δ (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5). The high oxygen nonstoichiometry, δ = 0.18-0.43 at 700 °C, indicates the large oxygen vacancy concentrations in oxides. The electrical conductivity is improved due to the greater amount of electronic holes originated from the increased interstitial oxygen, and the conductivities of all samples are above 100 S cm−1 at 400-700 °C in air. The results demonstrate the promising performance of YBa1−xSrxCo2O5+δ cathodes at intermediate temperatures, as evidenced by low area-specific resistances (ASRs) e.g. 0.21-0.59 Ω cm2 at 700 °C. The lowest ASR, 0.44 Ω cm2, and the cathodic overpotential, −40 mV at a current density of −136 mA cm−2, are obtained in YBaCo2O5+δ cathode at 650 °C. The dependence of polarization resistance on oxygen partial pressure suggests that the charge transfer process is the rate-limiting step for oxygen reduction reaction in YBaCo2O5+δ cathode.