Solid Electrolyte Chemical Sensors for Aerospace Applications
Transcript of Solid Electrolyte Chemical Sensors for Aerospace Applications
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.
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Outline
• Background of Chemical Sensors at NASA GRC
• Solid Electrolyte Chemical Microsensors
- Oxygen sensors
- Carbon dioxide sensors
• Summary
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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
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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
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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
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2.50E-05
0 20 40 60 80 100 120 140
Time (min)
Cu
rre
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(A)
0.00E+00
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Time (min)
Cu
rre
nt
(A)
600°C, 1V
Oxygen Microsensor Testing Results
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12% 12% 12% 12% 12%
0.00E+00
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1.00E-05
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Time (min)
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rre
nt
(A)
600C, 1V
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0.00E+00
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0 10 20 30 40 50 60 70 80
Time (min)
Cu
rre
nt
(A)
600C, 1V
Oxygen Microsensor Repeatability Testing
12% in air
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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
)
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Oxygen Microsensor Current Vs. Log of Oxygen Concentrations
(Linear fitting from 0.025% to 0.7%)
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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)
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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
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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)
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Nanocrystalline Tin Oxide Improves Solid Electrolyte Carbon
Dioxide Sensor Performance
Sensor Responses Significantly Changed with Nanocrystalline Coating
0.00E+00
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Time (min)
Cu
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355°C, 1.5V4% CO2
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0 5 10 15 20 25 30 35 40 45 50
Time (min)
Cu
rre
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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
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Time (min)
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rren
t (A
)
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0 5 10 15 20 25 30
Time (min)
Cu
rren
t (A
)
4% CO2
405°C, 2V355°C, 3V
4% CO2
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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)
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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
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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
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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.