Elsevier

Journal of Alloys and Compounds

Volume 623, 25 February 2015, Pages 136-139
Journal of Alloys and Compounds

Electrochemical behavior of LSCF/GDC interface in symmetric cell: An application in solid oxide fuel cells

https://doi.org/10.1016/j.jallcom.2014.10.122Get rights and content

Highlights

  • Symmetric cell has been studied to understand electrode/electrolyte interface.

  • Powder synthesized at fuel to oxidant ratio of 2 possesses agglomerates of 74 nm.

  • TPR and TPO exhibit the reduction and oxidation behavior at 860 and 388 °C.

  • Symmetric cell shows charge transfer resistance of 6.3 Ω cm2 at 550 °C.

Abstract

In present paper, La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF)/Ce0.9Gd0.1O1.95 (GDC)/LSCF structure has been studied to understand electrode/electrolyte interface. The nanocrystalline powder required for screen printing was obtained through solution combustion synthesis with glycine as a fuel. The LSCF powder synthesized at fuel to oxidant ratio of two is calcined at 900 °C as TG–DTA reveals thermal stability only beyond 900 °C. The X-ray diffraction pattern of calcined powder demonstrates rhombohedral perovskite structured LSCF with 27 nm crystallite size. However, dynamic laser scattering shows 0.9 μm sized agglomerates while TEM shows 74 nm particles. For potential application in solid oxide fuel cells, the temperature programmed reduction and oxidation were done on the LSCF. The results exhibit strong reduction and oxidation behavior around 860 and 388 °C, respectively. The cell with LSCF as an electrode shows minimum charge transfer resistance of 6.3 Ω cm2 at 550 °C.

Introduction

The operating temperature of solid oxide fuel cell (SOFC) should be low in order to improve material compatibility and reduce its cost [1]. Therefore, the main issue of recent research in SOFC is to reduce the operating temperature to 500–700 °C by preserving the oxygen reduction reaction (ORR) kinetics on cathode. However, decrease of operating temperature leads to slow oxygen diffusivity and surface exchange reaction and hence decreased ORR [2], [3]. Such a decreased ORR causes an adverse impact on activation and polarization losses and hence overall cell performance in intermediate temperature (IT) region. Thus, ORR should be enhanced either by achieving nanocrystalline particles with significant surface to volume ratio or by using highly conducting mixed ionic electronic conductors (MIEC) [4], [5]. Among the various types of MIEC materials, the perovskite based La0.6Sr0.4Co0.2Fe0.8O3−δ with general formula ABO3 is of great interest in IT-SOFCs due to its high oxygen permeability, chemical compatibility and matching of thermal expansion coefficient (TEC) with ceria based electrolytes i.e. Ce0.9Gd0.1O1.95 (GDC), Ce0.9Sm0.1O1.95 (SDC) [6], [7], [8]. Thus, the purpose of present research work is to synthesize the nanocrystalline LSCF powder by a solution combustion synthesis (SCS) route. The SCS has advantages of relatively simple method, cost effective, time saving and ability to form the phase pure materials at a low temperature [9], [10]. Since bulk cathodes have significant ohmic and polarization losses due to its larger size and less number of active sites for electrochemical reactions, the thick film of LSCF has been deposited on GDC to form symmetric cells. The chemical compatibility, microstructure and imperfection at the electrode/electrolyte interface due to difference in TEC have been studied in the symmetric cells.

Section snippets

Experimental

The Ce0.9Gd0.1O1.95 was prepared by a conventional solid state reaction route, using Gd2O3 and CeO2 as the starting materials. The powders were mixed together in an ethanol medium for homogenization and subsequently calcined at 700 °C for 2 h. The powder was then compacted under the hydraulic pressure of 110 MPa for 3 min. and sintered at 1300 °C for 8 h to achieve a reliable density of 93–96%. The pellets were polished with SiC paper to obtain smooth and parallel surface conditions.

The LSCF powder

Results and discussion

It is quite difficult to maintain the uniformity in combustion reaction thorough out the reacting mixture and unburned nitrates and carbonyl impurities are left behind. So to determine the calcination temperature for removal of these impurities, the TG–DTA of as synthesized powder was carried out. Fig. 1 shows the TG–DTA of LSCF powder synthesized at fuel to oxidant ratio of two. The measurement was carried out in air in a temperature range of 27–985 °C. The measurement shows the total weight

Conclusions

The nanocrystalline LSCF powder has been prepared through the solution combustion synthesis route at fuel to oxidant ratio of two. The XRD pattern of calcined powder reveals the rhombohedral perovskite structured LSCF with lattice parameters a = b = 5.509 Å and c = 13.371 Å. The TEM shows agglomerated particles of 74 nm size. The anodic and cathodic characteristics checked with TPR and TPO techniques show strong reduction and oxidation behavior around 860 and 388 °C, respectively. The LSCF/GDC/LSCF

Acknowledgments

This work is supported by DRDO. Also one of the authors, Mr. Atul P. Jamale, is thankful to UGC for providing the financial support through the UGC meritorious scheme.

References (25)

  • L.D. Jadhav et al.

    J. Alloys Comp.

    (2010)
  • N.J. Simrick et al.

    Solid State Ionics

    (2012)
  • S. Shahgaldi et al.

    J. Alloys Comp.

    (2011)
  • C.H. Li et al.

    Ceram. Int.

    (2012)
  • M. Zawadzki et al.

    Solid State Ionics

    (2010)
  • L.D. Jadhav et al.

    J. Alloys Comp.

    (2009)
  • A.U. Chavan et al.

    Ceram. Int.

    (2012)
  • A.P. Jamale et al.

    Appl. Surf. Sci.

    (2013)
  • Y. Dong et al.

    J. Eur. Ceram. Soc.

    (2011)
  • T. Prabhakaran et al.

    J. Alloys Comp.

    (2011)
  • S. Yang et al.

    J. Alloys Comp.

    (2008)
  • W. Chen et al.

    Mater. Lett.

    (2007)
  • Cited by (35)

    • Synthesis, structure and ionic conductivity of nanocrystalline Ce<inf>1−x</inf>La<inf>x</inf>O<inf>2−δ</inf> as an electrolyte for intermediate temperature solid oxide fuel cells

      2022, Journal of Alloys and Compounds
      Citation Excerpt :

      The XRD patterns do not show any other secondary phases corresponding to a chemical reaction between LDC and anode or cathode materials. Thus, the LDC samples are found to be compatible with NiO–GDC and LSCF, unlike in YSZ-LSCF composites [80]. Therefore, these LDC samples are chemically compatible even at much higher temperatures than required for fuel cell operation 600 − 800 °C.

    • Controlling cation migration and inter-diffusion across cathode/interlayer/electrolyte interfaces of solid oxide fuel cells: A review

      2021, Ceramics International
      Citation Excerpt :

      However, the interfacial stability and cation migration across the cathode/interlayer/electrolyte interfaces is not completely mitigated [77,92–100]. Remarkable efforts have been dedicated to investigating the origin, kinetics and influence of numerous factors on cation migration and enrichment near the cathode, interlayer, and electrolyte interface [45,55,77,92–94,101–118]. Moreover, the temperature-dependent interdiffusion between interlayer and electrolyte additionally affects the electrochemical performance of the SOFC [60,119–135].

    View all citing articles on Scopus
    View full text