Impedance Characterization of a Model Au∕Yttria-Stabilized Zirconia∕Au Electrochemical Cell in Varying Oxygen and NO[sub x] Concentrations

Woo, Leta; Martin, L.; Glass, Robert J.; Gorte, Raymond J.

doi:10.1149/1.2456328

Cited by 40 publications

(68 citation statements)

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“…Prior work has investigated solid-state electrochemical sensors for NO x based on yttria-stabilized zirconia (YSZ) electrolyte and an impedancemetric (sometimes referred to as impedimetric) sensing approach [9][10][11][12][13][14][15]. In contrast to the dc measurements made using amperometric (where current is measured and related to NO x concentration) or potentiometric (where voltages are measured and related to NO x concentration) approaches, the impedancemetric approach uses ac measurements at a specified frequency.…”

Section: Introductionmentioning

confidence: 99%

Diesel engine dynamometer testing of impedancemetric NO sensors

Woo

Glass

Novak

et al. 2011

Sensors and Actuators B: Chemical

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Prototype solid-state electrochemical sensors using a dense gold sensing electrode, porous yttria-stabilized zirconia (YSZ) electrolyte, and a platinum counter electrode (Au/YSZ/Pt) were evaluated for measuring NO x (NO and NO 2 ) in diesel exhaust. Both electrodes were exposed to the test gas (i.e., there was no reference gas for the counter electrode). An impedancemetric method was used for NO x measurements, where the phase angle was used as the response signal. A portion of the tailpipe exhaust from the dynamometer test stand was extracted and fed into a furnace containing the experimental sensor. The prototype sensor was tested along with a commercially available NO x sensor. Simultaneous measurements for NO x , O 2 , CO 2 , H 2 O, CO, and CH 4 in a separate feed stream were made using Fourier transform infrared (FTIR) spectroscopy and an oxygen paramagnetic analyzer. The experimental sensor showed very good measurement capability for NO in the range of 25-250 ppm, with a response paralleling that of the FTIR and commercial sensor. The prototype sensor showed better sensitivity to NO x at the lower concentration ranges. O 2 is an interferent for the experimental sensor, resulting in decreased sensitivity for measurement of NO x . Methods to overcome this interference are discussed.

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Section: Introductionmentioning

confidence: 99%

Diesel engine dynamometer testing of impedancemetric NO sensors

Woo

Glass

Novak

et al. 2011

Sensors and Actuators B: Chemical

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“…Briefly, impedancemetric operation has shown the potential to overcome the drawbacks of other approaches, including higher sensitivity towards NO x , better longterm stability, potential for subtracting out background interferences, total NO x measurement, and lower cost materials and operation. [8][9][10][11] Past LLNL research and development efforts have focused on characterizing different sensor materials and understanding complex sensing mechanisms. [8][9][10][11] Continued effort has led to improved prototypes with better performance, including increased sensitivity (to less than 5 ppm) and longterm stability, with more appropriate designs for mass fabrication, including incorporation of an alumina substrate with an imbedded heater.…”

Section: Future Directionsmentioning

confidence: 99%

“…The approach is described in detail in previous reports and several publications (See Ref. [8][9][10][11]. Briefly, impedancemetric operation has shown the potential to overcome the drawbacks of other approaches, including higher sensitivity towards NO x , better longterm stability, potential for subtracting out background interferences, total NO x measurement, and lower cost materials and operation.…”

Section: Future Directionsmentioning

confidence: 99%

“…The phase angle has been found to provide a more stable response at higher operating frequencies and is chosen as the sensor signal. [8][9][10][11] In previous work, impedancemetric sensing of either gold or strontium-doped lanthanum manganite (LSM), an electronically conducting metal oxide, electrodes was investigated in laboratory and engine testing. Preliminary results indicated that gold electrodes have good stability and the potential for low water cross-sensitivity, but also have a higher thermal expansion coefficient and lower melting temperature than the YSZ electrolyte, which limit processing flexibility.…”

Section: Introductionmentioning

confidence: 99%

“…[8][9][10][11] Past LLNL research and development efforts have focused on characterizing different sensor materials and understanding complex sensing mechanisms. [8][9][10][11] Continued effort has led to improved prototypes with better performance, including increased sensitivity (to less than 5 ppm) and longterm stability, with more appropriate designs for mass fabrication, including incorporation of an alumina substrate with an imbedded heater.Efforts in the last year to further improve sensor robustness have led to successful engine dynamometer testing with prototypes mounted directly in the engine manifold. Previous attempts had required exhaust gases to be routed into a separate furnace for testing due to mechanical failure of the sensor from engine vibrations.…”

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confidence: 99%

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NOx Sensor Development

Woo¹,

Glass²

2010

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Objectives• Develop an inexpensive, rapid-response, high-sensitivity and selective electrochemical sensor for oxides of nitrogen (NO x ) for compression-ignition, direct-injection (CIDI) exhaust gas monitoring• Explore and characterize novel, effective sensing methodologies based on impedance measurements and designs and manufacturing methods that could be compatible with mass fabrication• Collaborate with industry in order to (ultimately) transfer the technology to a supplier for commercialization Approach• Use an ionic (O 2− ) conducting ceramic as a solid electrolyte and metal or metal-oxide electrodes• Correlate NO x concentration with changes in impedance by measuring the cell response to an ac signal• Evaluate sensing mechanisms and aging effects on long-term performance using electrochemical techniques• Collaborate with Ford Research Center to optimize sensor performance and perform dynamometer testing Accomplishments• Modified sensor designs to successfully improve mechanical robustness for withstanding engine vibrations and prevent failure during engine/vehicle dynamometer testing• Developed a preliminary strategy to mitigate major noise factors and improve accuracy by quantifying effects of temperature, water, and oxygen to generate a numerical algorithm• Publications/Presentations: Future Directions• Continue developing more advanced prototypes suitable for cost-effective, mass manufacturing• Continue evaluating performance of prototypes, including long-term stability and cross-sensitivity, in laboratory, dynamometer, and on-vehicle tests• Continue efforts to initiate the technology transfer process to a commercial entity Because the need for a NO x sensor is recent and the performance requirements are extremely challenging, most are still in the development phase. [4][5][6] Currently, there is only one type of NO x sensor that is sold commercially, and it seems unlikely to meet more stringent future emission requirements.Automotive exhaust sensor development has focused on solid-state electrochemical technology, which has proven to be robust for in-situ operation in harsh, high-temperature environments (e.g., the oxygen stoichiometric sensor). Solid-state sensors typically rely on yttria-stabilized zirconia (YSZ) as the oxygen-ion conducting electrolyte and then target different types of metal or metal-oxide electrodes to optimize the response. [2][3][4][5][6] Electrochemical sensors can be operated in different modes, including amperometric (a current is measured) and potentiometric (a voltage is measured), both of which employ direct current (dc) measurements. Amperometric operation is costly due to the electronics necessary to measure the small sensor signal (nanoampere current at ppm NO x levels), and cannot be easily improved to meet the future technical performance requirements. Potentiometric operation has not demonstrated enough promise in meeting long-term stability requirements, where the voltage signal drift is thought to be due to aging effects associated with electrically driven changes...

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Electrochemical Sensors: Fundamentals, Key Materials, and Applications

Fergus

2009

Solid State Electrochemistry I

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Solid electrolytes are well suited for use in chemical sensors for high-temperature applications. The first such sensors followed from the use of solid electrolytes for thermodynamic measurements, and are based on galvanic cells, for which the open circuit voltage is related to the concentration of the mobile ionic species, or to another target species through equilibration at the electrode surface. However, sensors can also be based on nonequilibrium, but steady-state, potentials established between electrochemical reactions at the electrode. Another approach is to use the current passing through the electrolyte, rather than the voltage across the electrolyte, as the sensor signal. In this chapter we first describe the different methods for using solid electrolytes in chemical sensors, and then discuss some of the materials challenges and example applications. IntroductionMore than 50 years ago, Kiukkola and Wagner [1] demonstrated that solid electrolytes couldbeusedingalvaniccellstomeasurethethermodynamicpropertiesofoxides.Those pioneering studies subsequently led to the more practical application of solid electrolytes in chemical sensors. The ionic conduction in solid electrolytes is thermally activated and thus its rate increases with increasing temperature; consequently, solid electrolytes are well suited for high-temperature applications. On the other hand, such temperature dependencealsomeansthatsensorsbasedonsolidelectrolytescanrespondsluggishlyor may be inoperable at low temperatures. However, one of the advantages of solid-state devices, such as those based on solid electrolytes, is that they can be miniaturized [2,3]. Decreasingthedevicedimensionsreducesdiffusionlengths,whichinturndecreasesthe response time and thus also the minimum operating temperature.Ionic conducting solids can be used in a variety of different types of sensor [4][5][6][7][8][9][10][11][12]. Solids forwhichthe ionicconductivity is much largerthanthe electronic conductivity can Solid State Electrochemistry I: Fundamentals, Materials and their Applications. Edited by Vladislav V. Kharton

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Impedance Characterization of a Model Au∕Yttria-Stabilized Zirconia∕Au Electrochemical Cell in Varying Oxygen and NO[sub x] Concentrations

Cited by 40 publications

References 38 publications

Diesel engine dynamometer testing of impedancemetric NO sensors

Diesel engine dynamometer testing of impedancemetric NO sensors

NOx Sensor Development

Electrochemical Sensors: Fundamentals, Key Materials, and Applications

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