Atomic Layer Deposition of Zirconium Oxide for Fuel Cell Applications

UIC REU – Summer 2011AMReL Lab, UIC

Department of Bioengineering andDepartment of Chemical Engineering

Christine JamesUniversity of Michigan, Department of Chemical Engineering

Overview

• Background• Atomic Layer Deposition• Data Collected• Future Work

Fuel Cell Advantages

• Provides clean energy– Hydrogen fuel cells – only emit water

• Very efficient– Fuel Values

• Hydrogen: 141.8 kJ/g• Gasoline: 48 kJ/g • Coal: 15-27 kJ/g

Santhanam et al., Introduction to Hydrogen Technology, 2009, Hoboken, NJ: J. Wiley.

Fossil fuel

2007

Environmentally friendly

Coal 23 %

Nuclear Power 8 %

Renewable Energy 6 %

Petroleum 40 %

Natural Gas 23 %

Source: US Energy Information Agency

Sections of the Fuel Cell

• Cathode– Oxygen is reduced

• Anode– Hydrogen is oxidized

• Electrolyte– Transports the oxygen ions

www1.eere.energy.gov

SOFC FUEL CELL

Fuel In Air In

Unused Gases Out

Excess Fuel and

Water

Electrical Current

Solid Oxide Fuel Cells (SOFCs)• Current SOFCs are high temperature– Temperature: about 1000 °C

• Intermediate Temperature Fuel Cells– Temperature: 600-800°C– Smaller scale applications– Allows use of alternate materials– Starts and stops faster– Reduces corrosion – Offers a wide range of possibilities

Problem with Reducing Temperature• High temperatures needed to transport O2- ions – Requirement can be as high as 1200° C– Low temperatures cause ionic resistance

• Deposit electrolytes and analyze– Samples from atomic to bulk-like thickness– Method to be used:

• Atomic Layer Deposition

• Deposit oxide layers on silicon then platinum (Pt)

Approach

Atomic Layer Deposition (ALD)

www.cambridgenanotech.com/ald

H2O

Tri-methyl aluminumAl(CH3)3(g)

Methyl group(CH3)3(g)

Hydroxyl (OH) from surface absorbed H2O

Reaction of TMA with OH

Methane reaction product CH4

Chosen Precursor

www.aloha.airliquide.com

Niinistö, et al., Advanced Engineering Materials, 2009, 11, No.4, 223.

Precursors   Growth Temperature   ImpuritiesMetal Precursor O source   Range (°C) Preferred (°C) Saturation verified   C [-at%] H [-at%]

          at 300 °C      ZyALD Ozone   250-400 300 Yes   <1 N.R.

ALD System

ZyALD

ZyALD

Pulse and Purge times requiredReactor Temperature: 300°CBubbler Temperature: 50°CBubbler Pressure: 10 torrPrecursor: ZyALDPrecursor Pulse Time:

Precursor Purge Time:Oxidizer Pulse Time:Oxidizer Purge Time:Run for 40 cycles

Varied6 s

20 sVaried1.5 s

Varied

2 2.5 3 3.5 4 4.5 5 5.5 6 6.50.4

0.5

0.6

0.7

0.8

0.9

1

Precursor Pulse Time (s)

Gro

wth

Rat

e (Å

/cyc

le)

2 4 6 8 10 12 140.700000000000001

0.750000000000001

0.800000000000001

0.850000000000001

0.900000000000001

0.950000000000001

1

Precursor Purge Time (s)

Grow

th R

ate

(Å/c

ycle

)

10 s

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.80.600000000000001

0.650000000000001

0.700000000000001

0.750000000000001

0.800000000000001

0.850000000000001

0.900000000000001

0.950000000000001

1

Oxidizer Pulse Time (s)

Gro

wth

Rat

e (Å

/cyc

le)

12 13 14 15 16 17 180.600000000000001

0.650000000000001

0.700000000000001

0.750000000000001

0.800000000000001

0.850000000000001

0.900000000000001

0.950000000000001

1

Oxidizer Purge Time (s)

Gro

wth

Rat

e (Å

/cyc

le)

17 s

1 s

Varied

Zr

www.cambridgenanotech.com/ald

Temperature WindowReactor Temperature: VariedBubbler Temperature: 50°C

Bubbler Pressure: 10 torrPrecursor: ZyALD

50 100 150 200 250 300 350 4000

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

Temperature (°C)

Gro

wth

Rat

e (Å

/cyc

le)

Precursor Condensation Precursor Decomposition

Temperature Window

Comparison to Work from another group

225 250 275 300 325 3500

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

Temperature (°C)

Gro

wth

Rat

e (Å

/cyc

le)

Niinistö, et al., J. Mater. Chem. 18, 5243 (2008).

Thickness vs. Cycles RunReactor Temperature: 300°CBubbler Temperature: 50°C

Bubbler Pressure: 10 torrPrecursor: ZyALD

0 20 40 60 80 100 120 140 160 1800

20

40

60

80

100

120

140

160

Number of Cycles Run

Thic

knes

s (Å

) Slope: .87R² = 0.9973

Future Work

1. Deposit the zirconium oxide on Platinum2. Run electrochemical analysis

Silicon Substrate

Electrolyte: Zirconium Oxide

Platinum

Summary• Goal is to lower operating temperature of the fuel cell– By decreasing electrolyte layer thickness

• Atomic Layer Deposition (ALD) is being used• Have determined some necessary parameters:– Pulse and Purge times– Temperature Window for ALD

• Have compared cycles and thickness– Proved linear relationship

• Next Steps: – Deposit on Platinum – Run Electrochemical analysis

Acknowledgements

• National Science Foundation– EEC-NSF Grant # 1062943

• Graduate Mentor: Runshen Xu• Professor Takoudis and Professor Jursich