Energy and Power En gi neering, 2011, 3, 382-391
doi:10.4236/epe.2011.33049 Published Online July 2011 (http://www.SciRP.org/journal/epe)
Copyright © 2011 SciRes. EPE
Preparation of La0.6Ba0.4Co0.2Fe0.8O3 (LBCF) Nanoceramic
Cathode Powders by Sol-Gel Process for Solid Oxide Fuel
Cell (SOFC) Application
Yousef M. Al-Yousef, Mohammad Ghouse*
Energy Research Institute, King Abdulaziz City for Science and Technology (KACST), Riyadh, Saudi Arabia
E-mail: *msheikh@kacst.edu.sa, alyousef@kacst.edu.sa
Received January 29, 2011; revised March 14, 2011; accepted April 10, 2011
Abstract
The La0.6Ba0.4Co0.2Fe0.8O3 (LBCF) nano ceramic powders were prepared by Sol-Gel process using nitrate
based chemicals for SOFC applications since these powders are considered to be more promising cathode
materials for SOFC. Citric acid was used as a chelant agent and ethylene glycol as a dispersant. The powders
were calcined at 650˚C/6 h, 900˚C/3 h in air using Thermolyne 47,900 furnace. These powders were charac-
terized by SEM/EDS, XRD and Porosimetry techniques. The SEM images indicate that the particle sizes of
the LBCF powders are in the range of 50 - 200 nm. The LBCF perovskite phases are seen from the XRD
patterns. From XRD Line broadening technique, the average particle size for the powders (as prepared and
calcined at 650˚C/6 h and 900˚C/3 h) were found to be around 12.97 nm, 22.24 nm and 26 nm respectively.
The surface area of the LBCF powders for the as prepared and calcined at 650˚C were found to be 28.92 and
19.54 m2/g respectively.
Keywords: XRD, SEM/EDS, La0.6Ba0.4Co0.2Fe0.8O3 (LBCF), Porosimetry
1. Introduction
The Solid oxide fuel cells (SOFCs) are prominent candi-
dates of power generators that covert chemical energy
directly and with high efficiency, into electricity while
causing little pollution. These power generating systems
have attracted a considerable attention because of their
environmental friendliness, and fuel flexibility [1,2]. The
current status of the development of a cell unit is based
on yttria-stabilized zirconia (YSZ) solid electrolyte and
electrodes consisting of Sr-doped LaMnO3 (Cathode)
and Ni-YSZ cermet (Anode) [3,4]. Among the cathode
materials reported (La, Sr) MnO3 (LSM) based perov-
skite, due to their stability and high electrocatalytic ac-
tivity for oxygen reduction at high temperatures, are the
most extensively studied and investigated materials for
O2 reduction [5-9]. In spite of significant efforts by vari-
ous researchers, fundamental questions on the mecha-
nism and kinetics of the O2 reduction reaction and on the
electrode behavior of LSM materials under fuel-cell op-
eration conditions still remain unsolved. Although LSM
has shown promising performance for SOFC operating at
temperature around 800˚C, its performance decreases
rapidly as the operating temperature decreases [10].
Therefore, considerable research interest is currently di-
rected towards cobalt containing perovskite oxides which
tends to exhibit mixed-conduction characteristics and
relatively higher ionic conductivities than LSM due to a
greater concentration of oxygen vacancies [11-13]. Re-
cently, several new compositions that show mixed ionic
and electronic conductivity (MIEC) have been developed
as promising SOFC cathodes [14-17]. Amongst these,
the perovskite based compounds having the general for-
mula La1–xSrxM1–yCyO3, where 0 x 0.5 and 0 y
0.8 (M is a transitional metal Mn or Fe) has found wide
attention because of their superior MIEC behavior [15,16]
as well as enhanced oxygen reduction reactions (ORR)
kinetics [17-19].
Most recently Ba0.5Sr0.5Co0.8Fe0.2O3 (BSCF) oxide has
been found to exhibit excellent activity as a new cathode
material as reported in [20].Therefore replacing Sr with
Ba in LSCF would reduce Cr deposition according to the
proposed strategy [21,22] and to maintain high electro-
catalytic activity for O2 reduction reaction. Several re-
searchers have reported different techniques [23-24] for
preparing La0.6Ba0.4Co0.2Fe0.8O3 (LBCF) materials for
Y. M. AL-YOUSEF ET AL. 383
SOFC cathode materials due to their attractive properties.
Table 1 shows the suitable materials for SOFC compo-
nents [25].
The main design requirements for SOFC cathode ma-
terials [26] include: 1) High electronic conductivity; 2)
Chemically compatible with neighboring cell compo-
nents (electrolyte); 3) Stable in oxidizing environment; 4)
Large triple phase boundary; 5) High ionic conductivity;
6) Thermal expansion coefficient similar to other SOFC
materials; 7) Relative simple fabrication; 8) Relatively
inexpensive materials.
In this paper, nanocrystalline LBCF powders for
cathode material were prepared by the Sol-Gel process
since it is a simple and more economical way of making
nanopowders. The powders were characterized using
SEM/EDS, XRD, porosimetry techniques.
2. Experimental Procedure
2.1. Preparation of LBCF Powders
The La0.6Ba0.4Co0.2Fe0.8O3 (LBCF) nanoceramic powders
were prepared by modified Sol-Gel Process [27-29] us-
ing La(NO3)3 6H2O (BDH), Ba(NO3)2(BDH), Co(NO)3.
9H2O (Fluka), Fe(NO3)39H2O, citric acid (BDH) ethy-
lene glycol (BDH), ammonia solution and distilled water.
The precursor solution was prepared by mixing indi-
vidual aqueous solutions of the above chemicals in a
molar ratio of 0.6:0.4 and 0.2:0.8 respectively. To the
mixed all nitrate solutions, required citric acid, ammonia
solution and ethylene glycol were added. The citrate/
nitrate (c/n) ratio used in the present experiments was 0.5.
The solution was heated in a pyrex glass beaker on a
hotplate using magnetic stirrer until a chocolate colored
gel was formed. When heated further, the gel burns to a
light fragile ash. The ash was calcined at 650˚C/6 h, and
900oC/3h in air in a Barnstead Thermolyne 47900 Fur-
nace (USA). Figure 1 shows the flow Sheet for the
preparation of La0.6Ba0.4Co0.2Fe0.8O3 powder using the
Sol-Gel process. Table 2 shows cathode materials pre-
pared by the Sol-Gel process.
2.2. SEM/EDS Characterization
Small amounts of the samples were spread on adhesive
conductive aluminum tapes attached to sample holders,
coated with thin films of gold and examined with a FEI
Quanta 200 Scanning Electron Microscope. An attached
OXFORD INCA250 Energy Dispersive Spectroscopy
(EDS) unit was used to determine the area and spot ele-
mental compositions. Images at higher magnification
were collected with a FEI Quanta 3DF SEM. Imaging
was performed in Secondary Electron (SEI) mode only
using an accelerating voltage of 20 keV.
2.3. XRD Characterization
A part of the samples were analyzed with a PANnytical
X’Pert PRO XRD for phase characterization. The X-ray
diffractometry with CuK radiation at 35 KV and 20 mA
was used for phase analysis with a diffraction angle 2
theta range 10˚ - 80˚ and particle size determination from
X-ray line broadening technique using the following
Debye Scherrer Equation [30]:
t = 0.9λ/B cos Ø
where t = average particle size in nm, λ = the wave
length (0.15418 nm) of Cu Kα radiation, B the width (in
radian) of the XRD diffraction peak at half of its maxi-
mum intensity (FWHM), and Ø the Bragg diffraction
angle of the line, and B is the line width at half peak in-
tensity.
2.4. Porosimetry Characterization
2.4.1. Particle Size Distribution
Particle size distribution analysis was done using particle
size analyzer Mastersizer 2000 manufactured by Malvern
Instruments UK. This instrument works on the basis of
laser diffraction and is equipped with Hydro 2000S li-
quid feeder with a capacity of 50 to 120 ml. The feeder
has a built-in ultrasound probe with an inline pump and
stirrer. The instrument is capable to measure particle size
Table 1. Suitable materials for SOFC components [25].
Component Requirements Preferred Materials Possible Alternatives
Electrolyte
i > 0.05 S·cm1 ZrO2-Y2O3 (3 - 10 mol%) ZrO2-Sc2O3,
CeO2-Gd2O3, (Sm2O3)
Cathode >100 S·cm1 (electronic/mixed) La1–xSrx MnO3 (La1–x Srx)Co, FeO3
Anode >100 S·cm1 (electronic/ mixed) Ni/ZrO2-Y2O3
Ru/ZrO2-Y2O3
Ni/CeO2-ZrO2-M2O3 cermets
Interconnect Inert material, high temperature stabilityHigh temp. alloys La1–x (Sr ,Ca, Mg)xCrO3-
Manifold Non-volatile, inert Ceramics, metals -
Seal Non-volatile, inert Glass, glass-ceramic, Metal/ceramic -
C
opyright © 2011 SciRes. EPE
Y. M. AL-YOUSEF ET AL.
384
Lanthanum nitrate
Barium nitrate
Cobalt nitrate
Iron nitrate
Aqueous Solution
Citric Acid
Ethylene Glycol
Ammonia Solution
Heating on Hotplate
(Sol.Temp.100˚C)
Ash
Calcination of La
0.6
Ba
0.4
Co
0.2
Fe
0.8
O
3
Cathode Powders at 650˚C/6 hrs,
900˚C/3hrs in air
Dried Gel
Gel Formation
Figure 1. Flow sheet for the preparation of La0.6Ba0.4Co0.2Fe0.8O3 nanoceramic Cathode Powders by Sol-Gel process [27-29].
distribution within a range of 0.02 to 2000 μm. Distilled
water was used as a dispersant. The sample was added to
the dispersant to an obscursion limit in the range of 5% -
20%. The calculation of particle size distribution was
done using Mie theory. The samples were analyzed with
and without ultrasound probe. The above instrument
Copyright © 2011 SciRes. EPE
Y. M. AL-YOUSEF ET AL. 385
Table 2. LBCF cathode powders prepared by Sol-Gel proc-
ess.
Sample ID No Cathode Powder
#72 a, b La0.6Ba0.4Co0.2Fe0.8O3
#76 a, b, c La0.6Ba0.4Co0.2Fe0.8O3
LBCF: a: as prepared; b: calcined at 650˚C; and c: calcined at 900˚C.
measures the particle size distribution on the basis of
volume of sample particles.
2.4.2. Surface Area, Pore Volume and Pore Size
Measurement
The surface areas of samples were measured using an
Autosorb-1C instrument manufactured by Quanta Chrome,
USA. Samples were taken in the range of 0.1 - 0.2 g in a
cell and were degassed at 300˚C for 3 hrs to remove any
absorbed material on the surface. Nitrogen gas was used
as an adsorbent.The BJH cumulative adsorption method
was used to calculate pore volume cc/gr and pore size in
oA. The surface area (m2/g) of the powder as prepared
and calcined at 650˚C were calculated.
3. Results and Discussion
3.1. SEM/EDS Characterization
Figures 2(a)-2(c) show the nano-sized particles ob-
served by Scanning electron microscopy from the
La0.6Ba0.4 Co0.2 Fe0.8O3 (LBCF) powder samples cal-
cined under oxygen atmosphere at 650˚C and 900˚C
which were prepared with the Sol-Gel process using
metallic nitrates. It is seen in the SEM images that the
particles are homogeneous with the presence of highly
porous spherical particles with an approximate particle
size between 50 - 200 nm. It is noted from the figures
that the particle size of the calcined powders at 650˚C
and 900˚C are larger than the as prepared powders as
per expectation. It is also seen that by increasing the
calcination temperature a well defined crystal structure
develops (Figure 2). Figures 3(a) and 3(b) show the
EDS patterns of La0.6Ba0.4Co0.2 Fe0.8O3 powders. The
figures show the presence of La, Ba, Co, Fe, C, O peaks.
The residual C element from the citric acid that proba-
bly had not been combusted yet is shown in EDS in the
as prepared powder. However, the C content has been
reduced in the calcined powders at 900˚C. By increas-
ing the calcination temperature, the C is minimized
further. The wt% of C, La, Ba, Co, Fe and O are pre-
sented in the tables through EDS analysis.
(a)
(b)
(c)
Figure 2. (a) SEM image of LBCF Cathode Powder cal-
cined at 650˚C (#76b); (b) SEM image of LBCF Cathode
Powder calcined at 650˚C (#76b); (c) SEM image of LBCF
athode Powder calcined at 900˚C (#76c). C
C
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Y. M. AL-YOUSEF ET AL.
Copyright © 2011 SciRes. EPE
386
Processing option: all elements analysed (Normalised) #76b.
Spectrum In stats. C O Fe Co Ba La Total
A1 Yes 9.67 28.43 8.21 2.08 33.23 18.37 100.00
Mean 9.67 28.43 8.21 2.08 33.23 18.37 100.00
Std. deviation 0.00 0.00 0.00 0.00 0.00 0.00
Max. 9.67 28.43 8.21 2.08 33.23 18.37
Min. 9.67 28.43 8.21 2.08 33.23 18.37
All results in weight%.
(a)
Processing option: all elements analysed (Normalised) #76c
Spectrum In stats. C O Fe Co Ba La Total
A1 Yes 3.55 12.90 7.71 2.89 49.39 23.56 100.00
Mean 3.55 12.90 7.71 2.89 49.39 23.56 100.00
Std. deviation 0.00 0.00 0.00 0.00 0.00 0.00
Max. 3.55 12.90 7.71 2.89 49.39 23.56
Min. 3.55 12.90 7.71 2.89 49.39 23.56
All results in weight%.
(b)
Figure 3. (a) EDS of LBCF #76b (Calcined at 650˚C); (b) EDS of LBCF #76d (Calcined at 900˚C).
Y. M. AL-YOUSEF ET AL.
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387
3.2. XRD Characterization
Figures 4(a)-(c) show the XRD patterns of the as pre-
pared and calcined powders of La0.6Ba0.4Co0.2Fe0.8O3 at
650˚C and 900˚C respectively. It is seen that there are
expected phase present in the calcined powder. It is seen
that the calcined powder has well crystalline perovskite
phases of La0.6Ba0.4Co0.2Fe0.8O3. Table 3 shows the par-
ticle sizes of LBCF powders calcined at 650˚C and
900˚C. It is seen that the particle size is increased by
increasing the calcination temperatures as expected. The
average grain size of as prepared and calcined (at 650˚C
and 900˚C) powders are increased from 12 nm to 26 nm
respectively. The X-ray line broadening technique can be
used only for size determination of small crystallites
(~100 nm). The values obtained here may not be true
particle size. The crystallite size of the as prepared pow-
ders depends on the citrate to nitrate (c/n) ratio during
combustion process [31]. The XRD results obtained here
are in agreement with results reported elsewhere [23,24].
It is seen in Figure 4(c) that the crystalanity of the pow-
ders increased with sharp peaks by increasing the calci-
nation temperature. However, it is observed only small
Table 3. XRD Data to determine the average particle size of
the LBCF powders prepared by Sol-Gel.
S.no.2Ø B FWHM Particle size, t (nm)
76a 32.94 0.632 12.97
76b 32.32 0.368 22.24
76c 32.24 0.312 26.23
t = 0.9 × λ/B cos Ø, B = FHHM in o, B = [FWHM/180] × [22/7] = FWHM ×
0.017460, λ (Cu) = 0.15418 nm.
peaks which were attributed to the perovskite LaCoO3
phase which could be eliminated by employing high pu-
rity (99.99%) metal nitrate chemicals. Compared with as
prepared LBCF powder the XRD of calcined powder at
900˚C is more crystallized perovskite LBCF sharp phase
and could be used for cathode in SOFC application.
3.3. Porosimetry Characterization
Tables 4-7 show particle size (with and without ultra-
sound), average particle size, surface area , pore volume
and pore size of the LBCF powders as prepared and cal-
Figure 4. XRD pattern of La0.6Ba0.4Co0.2Fe0.8O3 Cathode Powder # 76, (a) As prepared; (b) Calcined at 650˚C; (c) Calcined at
00˚C. 9
Y. M. AL-YOUSEF ET AL.
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388
Table 4. Particle size distribution of La 0.6Ba0.4Co0.2Fe0.8O3
powders (with ultrasound).
Sample ID Number Volume Weighted Mean (μm)
With Ultrasound Without Ultrasound
72 (a) 59.604 77.601
72 (b) 27.060 59.087
Table 5. Surface area data of La0.6Ba0.4Co0.2Fe0.8O3 powders.
Sample ID Number Surface Area (m2/g)
72 (a) 28.92
72 (b) 19.54
Table 6. Pore volume data of La0.6Ba0.4Co0.2Fe0.8O3 pow-
ders.
Sample ID
Number BJH Method
Cumulative Pore Volume
(cc/g)
Adsorption 0.1168
72 (a)
Desorption 0.1198
Adsorption 0.1495
72 (b)
Desorption 0.1505
Table 7. Pore size data of La0.6Ba0.4Co0.2Fe0.8O3 powders.
Sample ID Number BJH Method Pore Size (ºA)
Adsorption 65.75
72 (a)
Desorption 38.33
Adsorption 22.42
72 (b)
Desorption 17.52
cined at 650˚C) respectively. Table 4 shows the average
particle size of the powders before and after calcination.
It is seen that without ultrasound the average particle size
for the powders for both as prepared and calcined at
650˚C is higher. Table 5 shows that the surface area of
the powders for as prepared and calcined at 650˚C are
28.92 m2/gr, 19.54 m2/gr respectively. It is seen that the
calcined powders have lesser surface are as expected.
The surface areas of the powders are similar to the sur-
face areas of the commercially available nano powders
[32]. From Table 6 it is observed that there is marginal
increase in the pore volume for calcined powder at 650˚C.
Table 7 shows the pore size data of LBCF powders for
adsorption (BJH method) has reduced for the calcined
powders at 650˚C. This may be again due to sintering at
650˚C and subsequently shrinkage might have occurred.
Figures 5(a)-(d) show the particle distribution of the
powders i.e. as prepared, calcined at 650˚C respectively.
It is seen from the Table 4 and Figures (5(a)-(d)) that
the ultrasounds helped break the large agglomerates and
narrowed the particle size distribution. Increasing the
calcination temperature increased particle size (agglome-
rate size), but ultrasounds fragment the aggregates which
indicates the agglomerates are soft which is observed due
to the preparation with either Sol-Gel or any other soft
chemical route like combustion synthesis. Actually with
increase in temperature the agglomerate size should in-
crease and surface area should decrease thereby. It is
observed that even if there is a chance of soft agglome-
rates forming at higher calcination temperature, the ef-
fect is nullified by ultrasounds. However this needs fur-
ther studies to correlate surface area results with particle
size distribution and calcination temperatures.
4. Conclusions
The following conclusions are drawn from the present
investigation:
The La0.6Ba0.4Co.2Fe0.8O3 (LBCF) nano ceramic pow-
ders for cathodes were successfully prepared by Sol-
Gel process with c/n ratio of 0.5.
SEM images indicate that the Particle size of LBCF
powders are in the range of 50 - 200 nm.
XRD patterns show the presence of the perovskite
La0.6Ba0.4Co0.2Fe0.8O3 phases.
Porosimetry analysis shows the surface area reduced
from ~28.92 m2/g to 19.54 m2/g with calcining the
powder at 650˚C.
5. Acknowledgements
Authors thank Dr. Naif M. Al-Abbadi, former Director,
Energy Research Institute, King Abdulaziz City for Sci-
ence and Technology (KACST), Riyadh, Saudi Arabia
for his encouragement and support during the course of
this work.
Also, author’s thanks are due to Mr. Mahmoud Al-
Manea and Dr. Shahreer Ahmad, Technology Center (TC),
Saudi Arabian Basic Industries Corporation (SABIC),
Jubail, Saudi Arabia for providing SEM/EDS result of
cathode powder samples. Author’s thanks are due to Dr.
Naseem Akhtar of Research Institute (RI), KFUPM,
Dhahran, Saudi Arabia for providing Porosimetry analy-
sis of the powders.
Also, author’s thanks are due to Mr. Haitham Al-
Gothami Technician, Atomic Energy Research Institute
(AERI) KACST, Riyadh, Saudi Arabia for providing
XRD analysis of Cathode powder samples. Author’s
thanks are due to Mr. Raed A. Al-Gumhan and Mr. Man-
sour Al-Saadan of Energy Research Institute, KACST
for their assistance during the experiments.
Y. M. AL-YOUSEF ET AL. 389
Particle Size Distribution
0. 0 1 0.1 1 10 100 1000 3000
Particle Size (µm)
0
1
2
3
4
5
Volume (%)
72-a - A verage, S und ay, A pri l 26, 2 009 11:1 4:34 A M
0
20
40
60
80
100
(a)
Particle Size Distribution
0. 0 1 0. 1 1 10 100 1000 3000
Particle Size (µm)
0
1
2
3
4
5
6
Volume (%)
72-a - A verage, S und ay, A pri l 26, 2 009 11:18: 24 A M
0
20
40
60
80
100
(b)
Particle Size Distribution
0. 0 1 0.1 1 10 100 1000 3000
Particle Size (µm)
0
1
2
3
4
5
6
Volume (%)
72-b - A verage, S und ay, A pri l 26, 2 009 11:4 7:25 A M
0
20
40
60
80
100
(c)
Particle Size Distribution
0. 0 1 0.1 1 10 100 1000 3000
Particle Size (µm)
0
1
2
3
4
5
6
7
8
Volume (%)
72-b - A verage, S und ay, A pri l 26, 2 009 11:4 9:59 A M
0
20
40
60
80
100
(d)
Figure 5. (a) Particle Size distribution of LBCF Cathode powders—without ultrasound; (b) Particle Size distribution of
LBCF Cathode powderswith ultrasound; (c) Particle size distribution of LBCF Cathode powders—w ithout ultrasound; (d)
article size distribution of LBCF Cathode powders—with ultrasound 72a: as prepared, 72b: clcined at 650˚C. P
C
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