Glenn Research Center at Lewis Field

Solid Electrolyte Chemical Sensors for

Aerospace Applications

Jennifer Xu and Gary Hunter

NASA Glenn Research Center

Chung-Chiun Liu

Case Western Reserve University

Benjamin Ward

Makel Engineering, Inc.

Glenn Research Center at Lewis Field 2

Outline

• Background of Chemical Sensors at NASA GRC

• Solid Electrolyte Chemical Microsensors

- Oxygen sensors

- Carbon dioxide sensors

• Summary

Glenn Research Center at Lewis Field 3

Background of Chemical Sensors at NASA GRC

• Sensors and platforms H2, CH4, C2H4, C3H6, CO2, CO, NOx, and N2H4

Schottky diodes, resistors, and electrochemical cells

• Approaches

Microfabrication, small size, low weight, cost, and power consumption. Batch fabrication, sensor arrays, smart sensor system and use as “Lick and Stick”

• Applications

Engine health and emissions monitoring, fuel leak detection, low false alarm fire detection, and environmental monitoring

Glenn Research Center at Lewis Field 4

Oxygen Microsensor Structure

0.99 mm

1.1

0 m

m

Partial Image of a fabricated

oxygen microsensor. One material system:

Yttria stabilized zirconia (YSZ)

AutoCAD drawing of an interdigitated

electrode structure and two contacts

Glenn Research Center at Lewis Field 5

0.5%

1%

2%

4%

8%12%

16% 21%

0.00E+00

5.00E-06

1.00E-05

1.50E-05

2.00E-05

2.50E-05

0 20 40 60 80 100 120 140

Time (min)

Cu

rre

nt

(A)

600°C, 1V

0.5%

1%

2%

4%

8%12%

16% 21%

0.00E+00

5.00E-06

1.00E-05

1.50E-05

2.00E-05

2.50E-05

0 20 40 60 80 100 120 140

Time (min)

Cu

rre

nt

(A)

0.00E+00

5.00E-06

1.00E-05

1.50E-05

2.00E-05

2.50E-05

0 20 40 60 80 100 120 140

Time (min)

Cu

rre

nt

(A)

600°C, 1V

Oxygen Microsensor Testing Results

Glenn Research Center at Lewis Field 6

12% 12% 12% 12% 12%

0.00E+00

5.00E-06

1.00E-05

1.50E-05

2.00E-05

2.50E-05

0 10 20 30 40 50 60 70 80

Time (min)

Cu

rre

nt

(A)

600C, 1V

12% 12% 12% 12% 12%

0.00E+00

5.00E-06

1.00E-05

1.50E-05

2.00E-05

2.50E-05

0 10 20 30 40 50 60 70 80

Time (min)

Cu

rre

nt

(A)

600C, 1V

Oxygen Microsensor Repeatability Testing

12% in air

Glenn Research Center at Lewis Field 7

Oxygen Microsensor Current Vs. Log of Oxygen Concentration

(Linear fitting from 0.5% to 16%)

0

5

10

15

20

25

30

0.10% 1.00% 10.00% 100.00%

Oxygen Concentration

Cu

rre

nt

(uA

)

Glenn Research Center at Lewis Field 8

Oxygen Microsensor Testing Results

Glenn Research Center at Lewis Field 9

Oxygen Microsensor Current Vs. Log of Oxygen Concentrations

(Linear fitting from 0.025% to 0.7%)

Glenn Research Center at Lewis Field 10

Al2O3 Substrate

Pt/Ti

electrode

Pt/Ti

electrode

e-

e- e-

e-

4e- + O2 2O2-

2O2– - 4e-

O2-

To air From air

2O2

O2-

O2-

YSZ cover Pt/Ti

Electrodes

Amperometric O2 Microsensor Sensing Mechanism

(Interdigitated electrodes simplified showing one pair of electrodes)

Glenn Research Center at Lewis Field 11

Solid Electrolyte Carbon Dioxide Microsensors

Pt interdigitated finger

electrode on Al2O3 substrate

0.99 mm

1.1

mm

Al2O3

NASICON NASICON NASICON Pt(+) Pt(-) Na2CO3/BaCO3

Side view of microfabricated CO2 sensor

(Simplified with two electrodes, patent filed)

SEM image of a

fabricated CO2 sensor

Carbon dioxide microsensor tested

at 600°C, 1V

Glenn Research Center at Lewis Field 12

Nanocrystalline Tin Oxide Coated to Reduce Solid Electrolyte

Carbon Dioxide Sensor Operation Temperature

Al2O3

NASICON NASICON NASICON Pt(+) Pt(-)

Na2CO3/BaCO3

Al2O3

NASICON NASICON NASICON Pt(+) Pt(-)

Na2CO3/BaCO3

SnO2 Nanocrystallines

Coated with SnO2 sol gel,

heated at 500°C for 2 hr

Side view of microfabricated CO2 sensor

Side view of microfabricated CO2 sensor

Coated with Nanocrystalline tin oxide

(Simplified with two electrodes, new tech. disclosed, patent filed)

Glenn Research Center at Lewis Field 13

Nanocrystalline Tin Oxide Improves Solid Electrolyte Carbon

Dioxide Sensor Performance

Sensor Responses Significantly Changed with Nanocrystalline Coating

0.00E+00

1.00E-09

2.00E-09

3.00E-09

4.00E-09

5.00E-09

6.00E-09

0 5 10 15 20 25 30 35 40 45 50

Time (min)

Cu

rre

nt

(A)

355°C, 1.5V4% CO2

0.00E+00

1.00E-09

2.00E-09

3.00E-09

4.00E-09

5.00E-09

6.00E-09

0 5 10 15 20 25 30 35 40 45 50

Time (min)

Cu

rre

nt

(A)

355°C, 1.5V4% CO2

2.00E-09

3.00E-09

4.00E-09

5.00E-09

6.00E-09

7.00E-09

8.00E-09

0 10 20 30 40 50 60

Time (min)

Cu

rre

nt

(A)

355°C, 2V4% CO2

Sensors after tin oxide sol gel addition

Sensors without tin oxide sol gel addition

0.00E+00

2.00E-09

4.00E-09

6.00E-09

8.00E-09

1.00E-08

1.20E-08

1.40E-08

0 5 10 15 20 25 30

Time (min)

Cu

rre

nt

(A)

2.00E-09

3.00E-09

4.00E-09

5.00E-09

6.00E-09

7.00E-09

8.00E-09

0 5 10 15 20 25 30

Time (min)

Cu

rren

t (A

)

2.00E-09

3.00E-09

4.00E-09

5.00E-09

6.00E-09

7.00E-09

8.00E-09

0 5 10 15 20 25 30

Time (min)

Cu

rren

t (A

)

4% CO2

405°C, 2V355°C, 3V

4% CO2

Glenn Research Center at Lewis Field 14

Nanocrystalline Tin Oxide Improve Solid Electrolyte

Carbon Dioxide Sensor

Solid Electrolyte CO 2 Sensor with Nanocrystalline SnO 2

(Detection temperature greatly reduced from 600 ° C to 375 ° C)

2

3

4

5

6

7

8

9

10

0 200 400 600 800 1000

Time (min)

Cu

rre

nt

(nA

)

0.5% 1% 1.5%

2%

2.7% 3.4% 4%

375 C, 2V

Glenn Research Center at Lewis Field 15

Sensing Mechanism of Solid State Electrochemical

Sensors for Carbon Dioxide Gases

Reduction site

Oxidation site

Al2O3

NASICON NASICON NASICON Pt(+) Pt(-)

Na2CO3/BaCO3

N-type Nanocrystallines SnO2

Reduction reaction at Pt(-) electrodes

2Na+ + CO2 +1/2 O2 + 2e- → Na2CO3

N-type metal oxides: supply more electrons or enhance

electrons flow

Results: Detection temperature decreased and power

consumption reduced

Glenn Research Center at Lewis Field 16

Summary

• Oxygen and carbon dioxide microsensors developed using same microsensor platform

• Oxygen sensor uses one sensing material system YSZ. By depositing the right thickness, YSZ can be both diffusion barrier and sensing material. Simplest sensor fabrication but wide oxygen detection was achieved: linear current response to the log of oxygen concentration from 0.025% to 16%

• Carbon dioxide sensor using two-material sensing system uniquely fabricated on interdigitated electrode, forming robust structure. Wide carbon dioxide detection achieved. Linear current response to the log of carbon dioxide concentration from 0.02% to 2% in air

• Solid electrolyte CO2 sensor improved and sensor power consumption decreased through addition of n-type SnO2 nanomaterial. CO2 operation temperature decreased from 600°C to 375°C. CO2 in air from 0.5% to 4% was tested

• Further improvement including expending sensor detection ranges and further reduce power consumption by reducing operation temperature.

• Oxygen and carbon dioxide microsensors can be used for aerospace applications such as fire detection and environmental monitoring.

Glenn Research Center at Lewis Field

Acknowledgements

Mike Artale, Peter Lampard, and Drago Androjna

Dorothy Lukco and Beth Osborn

Lawrence Matus and Mary Zeller

NASA Aviation Safety Program/IVHM Project

NASA ETDP/Space Fire Prevention Task