Characterization of La_(0.5)Sr_(0.5)Co_(0.5)Ti_(0.5)O_(3-δ) as symmetrical electrode material for intermediate-temperature solid-oxide fuel cells

摘要

La_(0.5)Sr_(0.5)Co_(0.5)Ti_(0.5)O_(3-δ) perovskite oxide has been prepared as polycrystalline powder, characterized and tested as cathode and anode material for solid-oxide fuel cells. The oxidized material is suggested to present mixed ionic-electronic conductivity (MIEC) from "in-situ" neutron powder diffraction (NPD) experiments, complemented with transport measurements; the presence of a sufficiently high oxygen deficiency, with large displacement factors for oxygen atoms suggest a large lability and mobility combined with a semiconductor-like behaviour with a maximum conductivity of 29 S cm~(-1) at T = 850 ℃. A complete reversibility towards reduction-oxidation processes has been observed, where the reduced Pm-3m perovskite withLa_(0.5)Sr_(0.5)Co_(0.5)Ti_(0.5)O_(2.64) composition has been obtained by topotactical oxygen removal without abrupt changes in the thermal expansion. The oxidized material shows good performance working as a cathode with LSGM electrolyte, yielding output power densities close to 500 mW/cm~2 at 850 ℃. At intermediate temperatures (800 ℃) it may be used as a cathode or as an anode, yielding power densities of 220 and 170 mW/cm~2, respectively. When used simultaneously as cathode and anode a maximum power density of 110 mW/cm~2 was obtained. Therefore, we propose the La_(0.5)Sr_(0.5)Co_(0.5)Ti_(0.5)O_(3-δ) composition as a promising candidate for symmetrical electrode in intermediate-temperature SOFC.