Chemical Degradation of the La0.6Sr0.4Co0.2Fe0.8O3−δ/Ce0.8Sm0.2O2−δ Interface during Sintering and Cell Operation

Mélanie François,Victoire Lescure,Maria Paola Carpanese,Frédéric Demoisson,Olivier Heintz,Gilles Caboche,Lionel Combemale,Davide Clematis

doi:10.3390/en14123674

Abstract

A complete cell consisting of NiO-Ce0.8Sm0.2O3−δ//Ce0.8Sm0.2O3−δ//(La0.6Sr0.4)0.95Co0.2Fe0.8O3−δ elaborated by a co-tape casting and co-sintering process and tested in operating fuel cell conditions exhibited a strong degradation in performance over time. Study of the cathode–electrolyte interface after cell testing showed, on one hand, the diffusion of lanthanum from (La0.6Sr0.4)0.95Co0.2Fe0.8O3−δ into Sm-doped ceria leading to a La- and Sm-doped ceria phase. On the other hand, Ce and Sm diffused into the perovskite phase of the cathode. The grain boundaries appear to be the preferred pathways of the cation diffusion. Furthermore, a strontium enrichment was clearly observed both in the (La0.6Sr0.4)0.95Co0.2Fe0.8O3−δ layer and at the interface with electrolyte. X-ray photoelectron spectroscopy (XPS) indicates that this Sr-rich phase corresponded to SrCO3. These different phenomena led to a chemical degradation of materials and interfaces, explaining the decrease in electrochemical performance.

Highlights

One of the current global challenges is to find novel, clean and efficient techniques for energy production
Impedance measurement of a Ni-SDC//SDC//La0.6 Sr0.4 Co0.2 Fe0.8 O3−δ (LSCF) cell fabricated by a cost-effective process consisting of co-tape casting and co-sintering showed a strong degradation in performance after the first 40 h of operation
That lanthanum diffused into the SDC electrolyte layer while cerium and samarium diffused into the cathode layer, the preferred diffusion paths appearing along the grain boundaries

Summary

Introduction

One of the current global challenges is to find novel, clean and efficient techniques for energy production. Classical SOFC systems based on yttria-stabilized zirconia (YSZ) as electrolyte operate at high temperatures, typically more than 800 ◦ C, leading to low durability. When associated with lanthanum strontium manganite (LSM), YSZ tends to form SrZrO3 or La2 Zr2 O7 interfacial insulating phases during the sintering process [2,3]. Such high temperatures imply the use of expensive interconnect materials such as LaCrO3 [4]. To allow greater durability of cells and promote their insertion into the energy market, it is necessary to decrease the working temperature

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Discussion

Conclusion