Nature and Functionality of La_0.58Sr_0.4Co_0.2Fe_0.8O_3-δ/ Gd_0.2Ce_0.8O_2-δ/ Y_0.16Zr_0.84O_2-δInterfaces in SOFCs

Abstract

Interdiffusion phenomena and secondary phase formation at the interface La 0.58 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF) / Gd 0.2 Ce 0.8 O 2-δ (GDC) / Y 0.16 Zr 0.84 O 2-δ (YSZ) are correlated to linear and non-linear losses in symmetrical and full SOFC cells. FIB/SEM (focussed ion beam / scanning electron microscopy) tomography is applied for determining the local distribution of the primary phases LSCF, GDC, and YSZ and elemental analysis via STEM/EDXS (scanning transmission electron microscopy / energy dispersive X-ray spectroscopy) provides information on the secondary phase SrZrO 3 (SZO) and the interdiffusion between GDC and YSZ (ID). This reveals the effect of GDC co-sintering temperature (varied from 1100 • C to 1400 • C), alongside the sintering of LSCF at 1080 • C, on these multi-layered microstructures. Electrochemical impedance spectra on symmetrical cells show that the polarization resistance (ASR cat) of the cathode/electrolyte interface is pronouncedly affected by three orders of magnitude, changing the overall power density of anode supported SOFC single cells at 0.8V by as much as a factor of 20. In conclusion, the chemical composition of the ID has a tremendous impact on the electrochemical efficiency of the investigated LSCF/GDC/YSZ interface, and processing parameters of anode supported cells with LSCF cathode have to be carefully chosen for individual SOFC cell concepts.

Degradation Analysis of Solid Oxide Fuel Cells with (La,Sr)(Co,Fe)O3-δ Cathode/Gd2O3–CeO2 Interlayer/Y2O3–ZrO2 Electrolyte System: The Influences of Microstructural Change and Solid Solution Formation

“…[20][21][22] Degradation factors ii) and iii) mainly reflect the reduction in electrochemically-active reaction sites. 22 Although the last factor iv) has been recognized well, 19,[23][24][25][26][27] the influence of the ceria-zirconia solid solution formation on the cell performance has not been elucidated sufficiently.…”

Achievements of NEDO Durability Projects on SOFC Stacks in the Light of Physicochemical Mechanisms

“…On the other hand, high temperature heat treatment is needed to sinter DC in dense films in a usual industrial method, and this promotes inevitably the interdiffusion between DC and YSZ , , resulting in decrease in ionic conductivity in the intermediate composition region . Furthermore, more complicated features have been clarified about the processing of the LSCF/DC/YSZ layers from the fundamental investigations on the mass transportation associated with the SrZrO 3 formation , , . These can be summarized as follows: When GDC is dense, chemical reactions between GDC and LSCF do not proceed so that no changes occur in the GDC side.…”

“…Without intentional humidification, there can be some amount of water vapors available during fabrication and operation so that the gaseous Sr transportation as the form of Sr(OH) 2 may also contribute in addition to the surface or gb diffusion to the GDC/YSZ interfaces. In many cases, formed SrZrO 3 phase contains some parts of Co and Fe , . The dense PLD film of GDC exhibits quite different behaviors in chemical reactions or diffusion. This is partly because defects in the PLD film are different from those in sintered body and partly because some cerium ions are present as Ce 3+ in the PLD film which remain even after the process of the LSCF attachment around 1,100 °C.…”

“…Without intentional humidification, there can be some amount of water vapors available during fabrication and operation so that the gaseous Sr transportation as the form of Sr(OH) 2 may also contribute in addition to the surface or gb diffusion to the GDC/YSZ interfaces. In many cases, formed SrZrO 3 phase contains some parts of Co and Fe [28,[86][87][88]. (iii) The dense PLD film of GDC exhibits quite different behaviors in chemical reactions or diffusion.…”

“…Then Gd 2 Zr 2 O 7 will be the next compound to be checked. Figure A2a shows the reported diffusion profile between YSZ and Y doped ceria (YDC) [79,80], while Figure A2b shows corresponding logarithmic activities of ZrO 2 , CeO 2 , and YO 1.5 evaluated using the thermodynamic properties which were optimized to reproduce the immiscibility observed at 1,273 K [86]. Figure A2c is the diffusion path plotted on the triangle phase diagram for the ZrO 2 -CeO 2 -YO 1.5 system.…”