Interaction of La0.8Sr0.2MnO3 interlayer with Gd0.1Ce0.9O1.95 electrolyte membrane and Ba0.5Sr0.5Co0.8Fe0.2O3−δ cathode in low-temperature solid oxide fuel cells
Introduction
The high temperature fabrication and operation of solid oxide fuel cells (SOFCs) lead to elemental diffusions and reactions between different phases and layers, which have a great impact on the cell performances. Our previous researches on the anode-supported La0.9Sr0.1Ga0.8Mg0.2O2.85 (LSGM)–La0.45Ce0.55O2 (LDC) bi-layered electrolyte cell depicted that this cell had lower open-circuit voltage (OCV) and lower specific ohmic resistance than expected, which can be assigned to the diffusion of Co from La0.6Sr0.4CoO3 (LSC) cathode to LSGM electrolyte [1], [2], [3]. A work on an all-perovskite fuel cell done by Tao et al. [4] suggested that a slight cross-diffusion at the interfaces between different perovskite components might improve the interfacial contact and decrease the interfacial resistance. La cations could diffuse into yttria-stabilized zirconia (YSZ) electrolyte from Sr-doped lanthanum manganite (LSM) cathode, which lowered the cathode performance [5], [6]. Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF)–LaCoO3 (LC) composite cathode had the higher electronic conductivity than the single BSCF cathode because of the solid-state reaction between BSCF and LC [7].
Recently, we fabricated a low-temperature solid oxide fuel cell with a La0.8Sr0.2MnO3 (LSM) interlayer between Ce0.9Gd0.1O1.95 (GDC) electrolyte membrane and Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF)–GDC composite cathode, and this cell showed the improved cell performance than the unmodified one [8]. In this cell, the elemental diffusion from BSCF cathode to LSM interlayer seems to play an important role. Of course, at a specific sintering temperature of LSM interlayer, the interaction between LSM and BSCF depends on the sintering temperature of the BSCF–GDC composite cathode. In this paper, the interaction between LSM interlayer and GDC electrolyte as well as BSCF cathode is investigated, and its effects on cell performance are elucidated.
Section snippets
Materials synthesis and cell fabrication
The home-made BSCF, LSM and GDC powders were synthesized by the sol–gel process. Anode-supported thin electrolyte (20 μm) bi-layer assemblies were fabricated using a dual dry-pressing method. The anode, consisted of a 50:50 wt.% mixture of NiO and GDC powders was dry-pressed into a pellet, and then an appropriate amount of the GDC electrolyte powder was distributed on the anode surface and co-pressed with the anode using a uniaxial die-press (Ø25 mm). The resultant bi-layer was sintered at 1420 °C
SEM/EDX analysis of a model LSM/BSCF bi-layer pellet
Information on the possible elemental inter-diffusion between LSM interlayer and BSCF cathode layer can be provided by examining a model LSM/BSCF bi-layer pellet through microanalysis. Fig. 1a shows the microstructure of the model LSM/BSCF pellet. It can be observed that the pellet is not densely sintered after the thermal treatment. For this reason, the elemental profiles presented in Fig. 1b can only be used for semi-quantitative statements. As shown in Fig. 1b, a distinct congregation of all
Conclusions
Low-temperature SOFCs with LSM interlayer between GDC electrolyte membrane and Ba0.5Sr0.5Co0.8Fe0.2O3 (BSCF)–GDC cathode were fabricated at the cathode sintering temperature of 900, 950 and 1000 °C. The EDX line scan analysis of a model LSM/BSCF double layer identified the transport of Co, Ba and Fe from BSCF into LSM, and simultaneous migration of Mn and La from LSM to BSCF. XRD results also suggested the inter-diffusion between LSM interlayer and GDC electrolyte as well as BSCF cathode. LSM
Acknowledgements
The authors gratefully acknowledge financial supports from the Ministry of Science and Technology of China (nos. 2004CB719506, 2005CB221404 and 2006AA05Z147), National Natural Science Foundation of China (Grant No. 20676132) and Europe Commission (SOFC 600). Also Min Yang wishes to thank Junbo Hou for useful discussion.
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