Third Day Poster Session, 17 June 2010 - NanoTR-VI

Poster Session, Thursday, June 17
Theme F686 - N1123
Undesired Phase Formations Between Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-δ Cathode and La 0.9 Sr 0.1 Ga 0.8 Mg 0.2 O 2.85
Electrolyte for SOFCs
Yeliz EKINCI 1 , Ridvan DEMIRYUREK 2* , Omer KARAKOC 2* , Shalima SHAWUTI 2 , Cinar ONCEL 2 and M. Ali GULGUN 2
1 Faculty of Chemical and Metallurgical Engineering, Istanbul Technical University, Istanbul 34469, Turkey
2 Faculty of Engineering and Natural Sciences, Sabanci University, Istanbul 34956, Turkey
Abstract Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-δ (BSCF) is promising material as a cathode for La 0.9 Sr 0.1 Ga 0.8 Mg 0.2 O 2.85 (LSGM) based SOFCs. For this aim,
BSCF-LSGM powders were characterized by the XRD, SEM and EDS techniques to observe the formation of undesired phases in the
temperature range of 700-1100 °C. Formation of new phases began around 900 °C. No new phases were observed below this temperature.
SrLaGa 3 O 7 , BaLaGaO 4 and Ba 6 La 2 Co 4 O 15 could be undesired phases which were strongly observed at 1100 °C.
The main obstacle in front of SOFC’s commercialization
is their high operating temperatures [1]. Efforts to reduce the
operating temperature brings along some problems with them.
There is a substantial increase in electrochemical resistance of
the fuel cell components (anode, cathode and electrolyte) and
an increase of electrode polarization resistance [2]. To tackle
these problems, novel materials has been under an intense
studies. Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3−δ (BSCF) cathode and
La 0.9 Sr 0.1 Ga 0.8 Mg 0.2 O 2.85 (LSGM) electrolyte material
combination offers promising results. LSGM is preferred
because of its high oxygen ion conductivity, 10 -1 S cm -1 [3] at
800 °C and high oxygen diffusion rate. The electronic
conductivity pattern over a wide range of oxygen partial
pressures (10 − 20 to 1 atm) can be assumed negligible at
intermediate operating temperatures [3]. BSCF is a mixed
oxygen ionic and electronic conducting oxide in the lattice
form of perovskite [2]. High activity to reduce the oxygen
electrochemically and high oxygen diffusion rate at 773-873
°C makes BSCF worthy of investigation [3]. However use of
BSCF cathode and LSGM electrolyte together may cause
formation of some undesired phases. These undesired phases
could decrease the efficiency of the whole system.
In this investigation, the temperature range at which
undesired reactions between the cathode candidate and the
LSGM electrolyte take place and the phases that are formed
were studied. BSCF used in this study was synthesized by
combined EDTA-citrate (EC) method [4]. The temperature of
the formation of reaction products was determined by XRD.
LSGM and BSCF powders are mixed in the ratio of 1:1. XRD
measurements are done on the powders heat treated at room
temperature (RT), 700 C, 800 C, 900 C, 1000 C, and 1100
C (Figure 1). Formation of new phases began around 900 C.
No new phases were observed below this temperature. The
phase that was strongly consumed in the reactions above 1100
°C was BSCF. The disappearance of XRD peaks belonging to
BSCF phase can be observed in Figure 1.
The new phases that form as a result of the reactions between
the cathode and electrolyte are suspected to be SrLaGa 3 O 7,
BaLaGaO 4 and Ba 6 La 2 Co 4 O 15 .
Figure 2 shows the secondary electron and back scattered
electron images of a particle that shows reacted as well as
original powder regions. EDS analyses taken from regions
with different BSE contrast in Figure 2 confirmed the
assignments of the phases that appear in these reactions. EDS
results also indicated that extensive solid solution in the
system is possible. This could open a whole new series of
mixed oxides that are suitable for SOFC applications.
Figure 2. SEM micrographs of mixture of BSCF-LSGM powders at
1100 °C (a) the secondary electron (b) the back scattered electron
*Presenting authors: demiryurek@su.sabanciuniv.edu,
okarakoc@su.sabanciuniv.edu
[1] Liu, B., Zhang, Y., and Zhang, L., 2008. Journal of Power
Sources. Volume 175, Issue 1, Pages 189-195
[2] Zhou, W., Ran, R., and Shao, Z., 2009. Journal of Power Sources,
Volume 192, Issue 2, Pages 231-246
[3] J. Peña-Martíneza, D. Marrero-Lópezb, J.C. Ruiz-Moralesb, B.E.
Buergler, P. Núñez and L.J. Gauckler, 2006. Solid State Ionics,
Volume 177, Issue 19-25, Pages 2143-2147
[4] Lee, S., Lim, Y., Lee, E., Hwang, H., and Moon, J, 2005. Journal
of Power Sources, Volume 157, Pages 848-854
(a)
(b)
Figure 1. The XRD patterns of mixture of BSCF-LSGM powders
6th Nanoscience and Nanotechnology Conference, zmir, 2010 770