Poster #120 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 Los Alamos National Laboratory Sensors and Electrochemical Devices Group, MPA-11 Los Alamos, New Mexico 87545 psekhar@lanl.gov 505 665 8996
Motivation • 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 H 2 safety assessments: The requirement to calibrate and commercialize safety sensors. Unclassified 2
Objectives • 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. Unclassified 3
DOE Technical Targets • 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: - 40 0 C to 60 0 C. • Durability: 5 years without calibration. • Cross-Sensitivity: Minimal interference to humidity, H 2 S, CH 4 , CO, and volatile organic compounds. Unclassified 4
Available Commercial H 2 Sensors H 2 Scan • 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 H 2 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. Unclassified 5
Available Commercial H 2 Sensors C-Squared Sensor • 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 other 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. Unclassified 6
Existing Technology - Challenges 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 H 2 safety sensors. Unclassified 7
Available Literature - Electrochemical H 2 Sensors Unclassified 8
Mixed Potential Sensor - Concept Oxygen + V 500 0 C NO / NO 2 / Electrode 2 Electrode 1 CO / H 2 / Oxygen ion conducting electrolyte C 3 H 6 ' P RT ( ) O2 E = ln '' 4F P O2 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) Unclassified 9
Unique LANL Design Dense Electrode Porous Electrode Porous Electrolyte Dense Electrolyte Dense Electrode Porous Electrode Commercial Sensor Design LANL Sensor Design • Dense Electrode, Porous Electrolyte – Stable Interface • Electrode with large difference in oxygen reduction kinetics • Gas diffusion through less catalytically active electrolyte Unclassified 10
Experimental – Device Fabrication • Substrate – Alumina with Integrated Pt heater at Rear from ESL Electroscience Laboratories • Working Electrode: Indium Tin Oxide (90 In 2 O 3 : 10 SnO 2 ), Sputtering • Counter Electrode: Pt, Sputtering • Electrolyte: Yttria-Stabilized Zirconia (YSZ) , E-beam Evaporation Unclassified 11
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: H 2 ,NO, NO 2 , NH 3 , C 3 H 6 , and CO Unclassified 12
H 2 Sensor Response 0.2 6.5 V, 200 SCCM, H 2 , 0 hrs 15000 ppm 10000 ppm 0.15 Sensor Response (V) 5000 ppm The sensor linearly responds to logarithmic 2500 ppm 0.1 concentrations of H 2 OFF ON ON 0.05 0 0 10 20 30 40 50 Time (mins) Unclassified 13
Cross-Interference 200 Intereference Study 150 Sensor Response (mV) Minimal interference 100 to NO, NO 2 , NH 3 , CO, and C 3 H 6 50 NO CO NO 2 100 100 100 ppm ppm ppm 0 H 2 C 3 H 6 C 3 H 6 NH 3 500 10000 100 100 ppm ppm ppm ppm -50 1 2 3 4 5 6 7 Analyte Gases Unclassified 14
Summary of Life Cycle Testing Unclassified 15
Life Cycle Results – Over 4000 hrs 0.2 50 0.5 % H 2 , 200 sccm, 6.5 V, 0.77 A 40 0.15 Response Rise Time (s) Sensor Response (V) 30 0.1 Sensor Signal Response Time 20 0.05 10 0 0 0 500 1000 1500 2000 2500 3000 3500 4000 Testing Time (hrs) Unclassified 16
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 H 2 oxidation slows down the reaction upon different thermal treatments. • Analyzing the overall device performance from 0 to 4000 hrs upon exposure to 5000 ppm of H 2 , (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. Unclassified 17
Conclusions • A pre-commercial H 2 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 optimized platinum electrode, the sensor response to 5000 ppm of H 2 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 H 2 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. Unclassified 18
Future Work • Postmortem analysis of H 2 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 H 2 sensor with a commercial device. Unclassified 19
Lanthanum Strontium Mangnate Electrode to Replace Pt Electrode Unclassified 20
Packaging and Comparison Testing Unclassified 21
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 of ITO as a H 2 sensing material. Unclassified 22
Recommend
More recommend
