Evaluation of layered perovskites YBa_(1-x)Sr_xCo_2O_(5＋δ) as cathodes for intermediate-temperature solid oxide fuel cells

摘要

This study is focused on the structural characteristics, oxygen nonstoichiometry, electrical conductivity, electrochemical performance and oxygen reduction mechanism of YBa_(1-x) Sr_xCo_2O_(5＋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 ℃, 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 ℃ in air. The results demonstrate the promising performance of _(1-x)Sr_xCo_2O_(5＋δ) cathodes at intermediate temperatures, as evidenced by low area-specific resistances (ASRs) e.g. 0.21-0.59 Ω cm~2 at 700 ℃. The lowest ASR, 0.44 Ω cm~2, and the cathodic over-potential, -40 mV at a current density of -136 mA cm~(-2), are obtained in YBaCo_2O_(5＋δ) cathode at 650 ℃. 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 YBaCo_2O_(5＋δ) cathode.