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• 12.5mL
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• In 300mL H2O
Introduction
Electrochemical Studies of Sol-Gel Processed
Perovskite Metal Oxides for Applications as SOFC
Cathode Materials
Jeff Roberts and Prof. Dan Thomas*
College of Physical & Engineering Science, University of Guelph
Fig. 1. Classical depiction of a) a SOFC as
well as b) a PEM fuel cell. It should be
noted that the only key difference between
the two is the electrolyte material, which
determines the type of ions that are
conducted and in what direction. The major
drawback of SOFCs is the high operating
temperature of 800ºC required to induce
oxygen ion flow.
Solid Oxide Fuel Cells (SOFCs) are an
attractive alternative to conventional Proton
Exchange Membrane (PEM) fuel cells, as
they allow for reduced manufacturing costs,
reduced fuel containment & distribution
costs, as well as increased efficiency.
La1-xSrxMnO3+δ (LSM) is a promising
candidate as a SOFC cathode material due
to its chemical/thermal compatibility with an
yttrium-stabilized zirconia (YSZ) electrolyte,
as well as its electronic conductivity and
possible oxygen ion conductivity.
Objectives
Is it feasible to create a mixed ionic-
electronic conductor in the form of a film that
is also resistant to thermal gradients and
mechanical stress?
• LSM films synthesized via sol-gel
processing are investigated
How does strontium doping affect film
conductivity?
• Perovskite LSM films synthesized and
analyzed using 4-point measurements
What effect does deposition method have on
film morphology?
• Spray pyrolysis compared to spin
coating/drop coating of sol-gel precursor
solution. Film morphology analyzed using
SEM
Fig. 2. Cross-sectional view of a SOFC
cathode-electrolyte interface, depicting the
three possible pathways of oxygen reduction
through the triple-phase boundary.
Methods
• 7.19g
Mn(NO3)2
• 1.59g
Sr(NO3)2
• 7.58g
La(NO3)3
• In 100mL
H2O
Sol. 1 Sol. 2
400mL Sol. 150mL “Gel” Heating 2h
with constant
stirring
Drop
Coating
Spin
Coating
Spray
Pyrolysis
Calcination
at 400˚C Sintering at
various
temperatures
LSM
Powder
LSM powders packed into 0.3-0.5mm
capillaries
Scanned from 0˚ to 180˚ 2θ
Methods
a) b) c)
Fig. 3. Images of LSM powders packed into a)
a 0.5mm capillary, b) a 0.3mm capillary, and c)
a flake of powder stuck to the stage with
vacuum grease. Sample c) had to be prepared
in this way because it was poorly packed into
a capillary that produced a noisy spectrum.
Results
Powder samples
adhered onto
disposable stage
using carbon
tape
Fig. 4. a) Disposable
metal stage for powder
characterization and b)
a standard Scanning
Electron Microscope
(SEM) / Energy
Dispersive
Spectrometer (EDS)
a) b)
Spin coated samples
and spray pyrolized
samples loaded
directly into chamber
on silicon substrates
Results
XRD spectra were extremely consistent with
literature spectra for perovskite structure
LSM. The minimum temperature required to
induce full crystallinity in the films was found
to be 600˚C.
Conclusions
Literature Cited
Acknowledgements
Fig. 8. Perovskite
unit cell.
Fig. 9. XRD spectrum
of pure perovskite LSM
from literature.
Fig. 10. XRD spectra taken of powders
sintered at various temperatures, showing the
sharpening of peaks at 600C̊ and above.
a) c) b)
Fig. 11. SEM images of films deposited using
spray pyrolysis. Sample a) was deposited on
an uncleaned silicon substrate, b) on a clean
silicon substrate, and c) was sintered for 2
hours at 1000C̊ on an uncleaned silicon
substrate.
Fig. 12. SEM image and corresponding EDS
spectrum of an LSM film spin coated onto a
silicon substrate and sintered at 450C̊.
Corresponds to a molar ratio La:Sr:Mn of
1.55:0.47:1. These results were equivalent
within error to the ideal x = 0.3 ratio of
1.77:0.48:1.
LSM gel with controllable molar ratio was
successfully created, and was found to form
very porous films of the desired perovskite
structure when spin coated and sintered
above 600˚C. Spray pyrolysis produced
consistent films composed of micron-sized
droplets that remained after a variety of
treatment. LSM(0.3) was found to have
temperature-dependent resistance consistent
with that of a semiconductor that minimized at
~250 Ohms. Future efforts would involve
decoupling oxygen ion conductivity from
electronic conductivity.
The author acknowledges the invaluable help
of Dr. Jay Leitch for allowing the use of the
nano-lab for a variety of characterization
techniques. Prof. Dan Thomas is also thanked
for providing valuable consultation,
supervision, and funding of the project.
Gaudon, M., Laberty-Robert, C., Ansart, F., Stevens, P.,
& Rousset, A. (2002). Preparation and
characterization of La1–xSrxMnO3 δ (0⩽x⩽0.6)
powder by sol–gel processing. Solid State
Sciences, 4, 125-133.
Yi, F., Chen, H., & Li, H. (2014). Performance of Solid
Oxide Fuel Cell with La and Cr Co-doped
SrTiO 3 as Anode. J. Fuel Cell Sci. Technol
Journal of Fuel Cell Science and Technology,
11(3), 031006-031006.
Fehribach, J., & O'hayre, R. (n.d.). Triple Phase
Boundaries in Solid-Oxide Cathodes. SIAM J.
Appl. Math. SIAM Journal on Applied
Mathematics, 510-530.
A modified Pechini method was selected to
produce the LSM gel due to the inexpensive
nature of the linking agents, low synthesis
temperature, and short time-scale of the
method. These features allow for industrial-
level scalability. a)
b)
Fig. 5. 4-point
voltage
measurement setup,
with each “point”
corresponding to a
gold lead.
Fig. 6.
Keithley sub-
femtoamp
sourcemeter,
with leads
attached
only to the
voltmeter.
Approximately 50nm of gold was deposited
epitaxially onto a drop-coated film of LSM(0.3)
on a quartz substrate in 4 evenly-spaced
strips. A small current was run between the
two outer strips while the resistance was
measured between the two inner strips. This
method eliminates any unknown resistance
associated with the probes.
Fig. 7.
Sample
LSM film
prepped for
resistance
analysis.
Samples were inserted into a tube furnace and
temperature was slowly ramped up to 700˚C
while measuring resistance every 2 seconds.
0
500
1000
1500
2000
2500
3000
0 5000 10000 15000 20000 25000
Re
sis
tan
ce
(O
hm
s)
Time (s)
LSM(0.3) Resistance vs Time with Increasing Temperature
100 ˚C
200 ˚C
300 ˚C 400 ˚C 500 ˚C 600 ˚C
1.5 ˚C /min ramp 2.5 ˚C /min ramp
0
500
1000
1500
2000
2500
3000
0 100 200 300 400 500 600 700
Re
sis
tan
ce
(O
hm
s)
Temperature (°C)
LSM(0.3) Resistance vs Temperature
Fig. 13. Resistance of LSM(0.3) as a
function of time and temperature.
Temperature was held constant for several
minutes in intervals of 100˚C in order to
unambiguously demonstrate the material’s
temperature-dependent resistance. These
breaks in temperature ramping are seen as
periodic plateaus in the plot of LSM(0.3)
resistance vs time.