Combinatorial development of nanocrystalline/amorphous (La,Sr)CoO3-(La,Sr)2CoO4 composite cathodes for IT-SOFCs

In this study, a combinatorial approach was used to develop cathode materials with improved performance at temperatures in the range 500-700 °C. A thin film composite cathode library was obtained by co-sputtering of LSC-113 and LSC-214 onto suitably positioned substrates each with controlled compositions. The cathode library was screened with an electrochemical impedance spectroscopy using symmetric cells. The study showed that the compositions with volume fractions in the range 0.40 < LSC-214 < 0.60 is particularly significant in yielding cathodes of improved performance. Refocusing the combinatorial screening to this range yielded LSC-113:LSC-214 = 0.45:0.55 as the most favorable compositions. Taking ASR = 0.15 Ω·cm2 as a useful benchmark, the study showed that cathodes in this range may be used at temperatures as low as 575 °C. It was further shown that composite cathodes have amorphous structures in co-sputtered conditions, and could remain so when used at reduced temperatures. At temperatures close to 700 °C the amorphous cathode turns into nanocrystalline two-phase structure with grains not more than 10 nm in size.