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

For the first time, anodes and cathodes composed of La0.3Sr0.7Fe1-xCrxO3-delta (LSFC, x = 0-0.3) are used within a symmetrical solid oxide fuel cell (SSOFC). La0.8Sr0.2Ga0.8Mg0.2O3-delta (LSGM) electrolyte-supported half cells, employing La0.3Sr0.7Fe0.7Cr0.3O3-delta (LSFC-3) at both electrodes, produced electrode polarization resistances of 0.1 Omega cm(2) in air and 0.4 Omega cm(2) in wet (ca. 3%H2O) H-2 at 800 degrees C. Although LSFC is robust under typical SSOFC conditions at 500 degrees C, in-situ X-ray diffraction studies at 800 degrees C in reducing atmospheres show that its perovkite structure can undergo a slow, pO(2)-dependent structural change, forming a LaSrFeO4-based Ruddlesden-Popper phase plus alpha-Fe, a process which can be reversed in air at 800 degrees C. For LSFC-3, this phase change occurs when the pO(2) of the fuel is lower than 1.9 x 10(-21) atm. This results in an initial power drop of ca. 30% for LSFC-3-based SSOFCs when using wet H-2, 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 H-2:CO fuels (pO(2) > 1.9 x 10(-21) atm) that contain 10 ppm H2S, demonstrating the excellent versatility of this electrode material. (c) 2013 Elsevier B.V. All rights reserved.