Sr-rich chromium ferrites as symmetrical solid oxide fuel cell electrodes

For the first time, anodes and cathodes composed of La_0.3Sr _0.7Fe_1-xCr_xO_3-δ (LSFC, x = 0-0.3) are used within a symmetrical solid oxide fuel cell (SSOFC). La _0.8Sr_0.2Ga_0.8Mg_0.2O _3-δ (LSGM) electrolyte-supported half cells, employing La _0.3Sr_0.7Fe_0.7Cr_0.3O _3-δ (LSFC-3) at both electrodes, produced electrode polarization resistances of 0.1 Ω cm² in air and 0.4 Ω cm² in wet (ca. 3%H₂O) H₂ at 800 ^oC. Although LSFC is robust under typical SSOFC conditions at 500 ^oC, in-situ X-ray diffraction studies at 800 ^oC in reducing atmospheres show that its perovkite structure can undergo a slow, pO₂-dependent structural change, forming a LaSrFeO₄-based Ruddlesden-Popper phase plus α-Fe, a process which can be reversed in air at 800^oC. For LSFC-3, this phase change occurs when the pO₂ of the fuel is lower than 1.9 × 10^-21 atm. This results in an initial power drop of ca. 30% for LSFC-3-based SSOFCs when using wet H₂, but the new anode composition still maintains a promising 0.2 W cm^-2 cell power density over several hundred hours of operation. Extended full cell tests also show that the LSFC-3 anode performs very well in wet 1:1 H₂:CO fuels (pO₂ > 1.9 × 10^-21 atm) that contain 10 ppm H₂S, demonstrating the excellent versatility of this electrode material.