Development of a Reliable and Miniaturized Hydrogen Safety Sensor - - PowerPoint PPT Presentation

Development of a Reliable and Miniaturized Hydrogen Safety Sensor Prototype

Praveen K. Sekhar, Eric L. Brosha, Rangachary Mukundan, Todd L. Williamson, and Fernando H.Garzon

Poster #120

Los Alamos National Laboratory Sensors and Electrochemical Devices Group, MPA-11 Los Alamos, New Mexico 87545 psekhar@lanl.gov 505 665 8996

• Recent developments in the search for renewable energy coupled with

the advancements in fuel cell powered vehicles have augmented the demand for hydrogen safety sensors.

• Variation in standard practice of H2 safety assessments: The

requirement to calibrate and commercialize safety sensors.

Motivation

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• Develop a low cost, low power, durable, and reliable Hydrogen

safety sensor for vehicle and infrastructure applications.

• Demonstrate working technology through application of

commercial and reproducible manufacturing methods and rigorous life testing results guided by materials selection, sensor design, and electrochemical investigation.

• Recommend sensor technologies and instrumentation approaches

for engineering design.

• Disseminate packaged prototypes to DOE Laboratories and

commercial parties interested in testing and fielding advanced commercial prototypes while transferring technology to industry.

Objectives

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• Sensitivity: 1 vol % in air.
• Accuracy: 0.04 - 4%  1%.
• Response Time: < 1 min at 1% and < 1 sec at 4%; recovery <1 min.
• Temperature: - 400 C to 600 C.
• Durability: 5 years without calibration.
• Cross-Sensitivity: Minimal interference to humidity, H2S, CH4, CO,

and volatile organic compounds.

DOE Technical Targets

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H2 Scan

Available Commercial H2 Sensors

• H2scan systems implement monitoring based on a patented “Chip on a

Flex” technology.

• The sensors utilize palladium alloy thin film based impedance change to

measure hydrogen in Parts Per Million (PPM) and H2 concentrations.

• The PPM level sensor incorporates a hydrogen specific capacitor and

the percent level sensor incorporates a hydrogen specific resistor.

• Hydrogen measurements are done in a molecular level using MOS

dual circuit configuration. H2scan’s hydrogen specific systems incorporate proprietary firmware and signal conditioning systems to display hydrogen levels in real time.

• No additional sampling or conditioning is necessary. A sophisticated

temperature control loop compensates for external temperature variations.

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• The Analyzer measures the Hydrogen content based on the extreme high

thermal conductivity of hydrogen gas.

• The unit consists of two main components: one is a sensor block and the
• ther is the electronic circuit.
• The patented design allows the unknown gas mixture to flow through the

sensing chamber and seal it inside for measurement.

• Once the gas mixture is sealed inside the sensing chamber, the

electronic circuit then measures the difference of the thermal conductivity between the gas mixture and the reference gas. The Hydrogen content is then calculated by the circuit and displayed. C-Squared Sensor

Available Commercial H2 Sensors

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Among the several sensing methods, electrochemical devices that utilize high temperature-based ceramic electrolytes are largely unaffected by changes in humidity and are more resilient to electrode or electrolyte

• poisoning. Further, engineering electrochemical devices enable long-

term stability and cost-effective solution to H2 safety sensors.

Existing Technology - Challenges

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Available Literature - Electrochemical H2 Sensors

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E = ln RT 4F

( )

P

O2

P

O2

'

''

Oxygen NO / NO2 / CO / H2 / C3H6

+

Oxygen ion conducting electrolyte Electrode 1 Electrode 2

V 5000 C Mixed Potential Sensor - Concept

Mixed potential sensors are a class of electrochemical devices that develop an open-circuit electromotive force due to the difference in the kinetics of the redox reactions of various gaseous species at each electrode/electrolyte/gas interface, referred to as the triple phase boundary (TPB)

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Commercial Sensor Design Porous Electrode Dense Electrolyte Porous Electrode LANL Sensor Design Dense Electrode Dense Electrode Porous Electrolyte

Unique LANL Design

• Dense Electrode, Porous Electrolyte – Stable Interface
• Electrode with large difference in oxygen reduction kinetics
• Gas diffusion through less catalytically active electrolyte

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Experimental – Device Fabrication

• Substrate – Alumina with Integrated Pt heater at Rear from ESL

Electroscience Laboratories

• Working Electrode: Indium Tin Oxide (90 In2O3: 10 SnO2), Sputtering
• Counter Electrode: Pt, Sputtering
• Electrolyte: Yttria-Stabilized Zirconia (YSZ) , E-beam Evaporation

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Testing

• Sensor electrodes and heater connected to four metal posts housed on

an alumina place holder and then inserted into a quartz tube

• Power: 6.5 V, 0.63 A
• Flow Rate: 200 sccm
• Humidity: 63%
• Test Gases: H2,NO, NO2, NH3, C3H6, and CO

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0.05 0.1 0.15 0.2 10 20 30 40 50

6.5 V, 200 SCCM, H2, 0 hrs

Sensor Response (V) Time (mins)

2500 ppm 5000 ppm 10000 ppm 15000 ppm

ON OFF ON

H2 Sensor Response

The sensor linearly responds to logarithmic concentrations of H2

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• 50

50 100 150 200 1 2 3 4 5 6 7 Intereference Study Sensor Response (mV) Analyte Gases

C3H6 500 ppm C3H6 100 ppm NH3 100 ppm CO 100 ppm NO2 100 ppm NO 100 ppm H2 10000 ppm

Cross-Interference

Minimal interference to NO, NO2, NH3, CO, and C3H6

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Summary of Life Cycle Testing

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0.05 0.1 0.15 0.2 10 20 30 40 50 500 1000 1500 2000 2500 3000 3500 4000

Sensor Signal Response Time

Sensor Response (V) Response Rise Time (s) Testing Time (hrs)

0.5 % H

2, 200 sccm, 6.5 V, 0.77 A

Life Cycle Results – Over 4000 hrs

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Life Cycle Results

• The variation in the sensor response subjected to different thermal

treatments can be attributed to thermal expansion mismatch between the electrodes (ITO, Pt) and the electrolyte (YSZ). For a typical ceramic-metal system involving high temperature applications, the recommended rule for materials selection involves the use of metal, that have similar and/or smaller thermal expansion coefficients than that of the ceramic.

• As the response time of the device is governed by the speed of the

competing oxygen reduction and electrochemical oxidation reactions, it is postulated that surface stress on ITO due to CTE mismatch and H2

• xidation slows down the reaction upon different thermal treatments.
• Analyzing the overall device performance from 0 to 4000 hrs upon

exposure to 5000 ppm of H2, (a) the sensitivity varied between 0.135 to 0.17 V with a minimum low of 0.12 V, (b) the baseline signal ranged from 0 to 0.04 V, and (c) the response rise time fluctuated between 3 to 47 s.

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• A pre-commercial H2 sensor prototype was fabricated on an alumina

substrate with ITO and Pt electrodes and YSZ electrolyte with an integrated Pt heater to achieve precise operating temperature and minimize heterogeneous catalysis.

• During the initial 4000 hrs of long-term testing for the prototype with
• ptimized platinum electrode, the sensor response to 5000 ppm of H2

varied at a maximum of ca. +10%/-7% from its original value of 0.135 V (0 hrs). The response rise time fluctuated between 3 to 47 s.

• The extended sensor response stability over time may be attributed to

a stable, engineered three-phase interface.

• The salient features of the investigated H2 sensor prototype include (a)

conducive to commercialization, (b) low power consumption, (c) compactness to fit into critical areas, (d) simple transduction mechanism, and (e) fast response.

Conclusions

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Future Work

• Postmortem analysis of H2 prototype sensor tested for 4000 hrs.
• Fabrication and lifetime performance evaluation (minimum 5000

hours) of advanced prototypes.

• Improved electrode material (Lanthanum Strontium Manganate) with

will be investigated for better long-term stability.

• Cross-sensitivity studies, stability evaluation using LSM electrodes in

advanced prototypes.

• Investigate and identify packaging schemes for field and laboratory

testing.

• Independent testing and comparison of the performance of packaged

prototype H2 sensor with a commercial device.

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Lanthanum Strontium Mangnate Electrode to Replace Pt Electrode

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Packaging and Comparison Testing

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Acknowledgements

DOE Hydrogen Fuel Cell and Infrastructure Programs, and Hydrogen Safety Codes and Standards supported the current sensor work. We thank Robert S. Glass and Leta Y. Woo from Lawrence Livermore National Laboratory for discussions on the use

• f ITO as a H2 sensing material.

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FY 2010 Publications and Presentations

• P.K.Sekhar, E.L.Brosha, R. Mukundan, T. L. Williamson, M.A.Nelson and

F.H.Garzon, “Development and Testing of a Hydrogen Safety Sensor Prototype”, Sensors and Actuators B, 148, 469 (2010).

• E.L.Brosha, P

.K.Sekhar, R.Mukundan, T.L.Williamson, F.H.Garzon, L.Y.Woo, and R.S.Glass, “Development of Sensors and Sensing Technology for Hydrogen Fuel Cell Vehicle Applications”, ECS Transactions, 26 (1), 475 (2010).

• P.K.Sekhar, E.L.Brosha, R. Mukundan, and F.H.Garzon, “Development of a

Reliable, Miniaturized Hydrogen Safety Sensor Prototype”, Fuel Cell Seminar and Exposition, Oct 18-22, 2010.

• L.Y.Woo, R.S.Glass, P.K.Sekhar, E.L.Brosha, R.Mukundan, M.A.Nelson and

F.H.Garzon, “Electrode Stability in Hydrogen Sensors Based on Yttria-Stabilized Zirconia Electrolyte”, 217th ECS Meeting in Vancouver, BC, Canada, April 2010.

• P.K.Sekhar, E.L.Brosha, R.Mukundan, M.A.Nelson and F.H.Garzon, “Electrical

Characterization of a Mixed Potential Sensor based on Indium Tin Oxide and Lanthanum Strontium Chromite Electrodes and Ytrria-Stabilized Zirconia Electrolyte”, 34th International Conference and Exposition on Advanced Ceramics and Composites, Jan 24-29, 2010.

• E.L.Brosha, P

.K.Sekhar, R.Mukundan, T.L.Williamson, F.H.Garzon, L.Y.Woo, and R.S.Glass, “Development of Sensors and Sensing technology for Hydrogen Fuel Cell Vehicle Applications”, 2009 Fuel Cell Seminar, Palm Springs, CA.

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