Development of cobalt-free LaxSr4-xFe6O13 (0<x<2) Intergrowth Cathode Material for Solid Oxide Fuel Cells

Abstract

Cobalt- free LaxSr4-xFe6O13 (0<x<2) oxide have been synthesized and investigated as a potential cathode material for solid oxide fuel cells (SOFCs). Sr4Fe6O13 consists of alternating perovskite layers (Sr4Fe2O8) containing iron cations in octahedral oxygen coordination and Fe4O5 layers where iron cations have 5-fold coordination of two types-square pyramids and trigonal bipyramids. Our prelinlinary electrochemical testes of pristine Sr4Fe6O13 show a rather high area specific resistance (0.47 Ocm2 at 700oC) for ~20 μm thick layers with CGO electrolyte. The electrochemical performances are improved by La addition up to x=1 (La1Sr3Fe6013 , 0.06 Ocm2 at 700oC) . In addition, thermal expansion coefficient (TEC) values of La1Sr3Fe6013 specimen demonstrated 15.1 x10-6 oC-1 in the range of 25-900oC, which provides good thermal expansion compatibility with the CGO electrolyte. An electrolyte supported (300-μm-thick) single-cell configuration of La1Sr3Fe6O13/CGO/Ni-CGO delivered a maximum power density of 584 mWcm-2 at 700oC. In addition, an anode supported single cell by YSZ electolyte (10-μm-thick) with a porous CGO interlayer between the cathode and the electrolyte to avoid undesired interfacial reactions exhibited 1,517 m Wcm-2 at 800oC. The unique composition of La1Sr3Fe6O13 with low theral expansion coefficient and higher electrochemical properties could be a good cathode candidate for intermediate temperature SOFCs with CGO and YSZ electrolyte.