• 50g Citric acid

C6H8O2

• 12.5mL

Ethylene

glycol

C2H4(OH)2

• 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.