Nanoscaled (La0.5Sr0.5)CoO3-δ thin film cathodes for SOFC application at 500°C < T < 700°C

Nanoscaled and nanoporous (La0.5Sr0.5)CoO3-delta (LSC) thin film cathodes (film thickness ranging from 200 to 300 nm, grain and pore size in the range of 50 nm) were electrochemically characterized to determine their potential for intermediate and low-temperature solid oxide fuel cells (SOFCs). Chemically homogeneous, large area (25 cm(2)), and nanoporous LSC thin films were derived from metallorganic precursors (metallorganic deposition) and deposited on yttria-doped zirconia [(YSZ) "design 1"] and gadolinia-doped ceria [(GCO) "design 2"]. The area-specific polarization resistance (ASR(pol)) of both designs was evaluated on symmetrical cells with special emphasis on constancy, depending on temperature (500-850 degrees C) and time by means of electrochemical impedance spectroscopy. For both designs, we report the capability of low polarization resistances, e. g., at 600 degrees C, 146 m Omega cm(2) (LSC/YSZ), respectively, 130 m Omega cm(2) (LSC/GCO). Oxygen reduction reaction was facilitated by a substantial inner surface area of the porous thin-film cathode, as suggested by the application of Adler's model. Nanoporous LSC thin-film cathodes from this study were compared to alternative design concepts for high-performance porous cathodes and with dense (La0.52Sr0.48)(Co0.18Fe0.82)O3-delta thin-film cathodes. Furthermore, the aim of our study was (i) to find a temperature regime with a perspective for chemical durability of an LSC/YSZ interface. We could prove that at a temperature of 500 degrees C and for 100 h, polarization resistance of the LSC/YSZ interface remains constant, and at unreported low values, which reopens LSC/YSZ for micro-SOFC application; (ii) to estimate the structural durability of nanoscaled and nanoporous LSC thin-film cathodes. We have been able to demonstrate stable and unreported low polarization resistance for LSC/GCO in the temperature range between 500 and 700 degrees C, which is of technical interest for auxiliary-power-unit application. (c) 2008 The Electrochemical Society.