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