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Title: Effect of Electrode Composition and Microstructure on Impedancemetric Nitric Oxide Sensors based on YSZ Electrolyte

Abstract

The role of metal (Au, Pt, and Ag) electrodes in YSZ electrolyte-based impedancemetric nitric oxide (NO) sensors is investigated using impedance spectroscopy and equivalent circuit analysis. The test cell consists of a rectangular block of porous YSZ with two metal wire loop electrodes, both exposed to the same atmosphere. Of the electrode materials, only Au was sensitive to changes in NO concentration. The impedance behavior of porous Au electrodes in a slightly different configuration was compared with dense Au electrodes and was also insensitive to NO. Ag showed no sensitivity to either O{sub 2} or NO, and the measured impedances occurred at frequencies > 10 kHz, which are typically associated with ionic conduction in YSZ. Pt and porous Au showed sensitivity to O{sub 2}, which was quantified using power-law exponents that suggest electrochemical rate-determining mechanisms occurring at the triple phase boundary. The behavior of the dense Au suggests different rate-determining processes (e.g., diffusion or adsorption) for the O{sub 2} reaction. Although the exact mechanism is not determined, the composition and microstructure of the metal electrode seem to alter the rate-limiting step of the interfering O{sub 2} reaction. Impedance behavior of the O{sub 2} reaction that is limited by processes occurringmore » away from the triple phase boundary may be crucial for impedancemetric NO sensing.« less

Authors:
; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
926046
Report Number(s):
UCRL-JRNL-229831
Journal ID: ISSN 0013-4651; JESOAN; TRN: US200807%%482
DOE Contract Number:
W-7405-ENG-48
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of the Electrochemical Society, vol. 155, no. 1, January 1, 2008, J32-J40; Journal Volume: 155; Journal Issue: 1
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ADSORPTION; CONFIGURATION; DIFFUSION; ELECTRODES; ELECTROLYTES; EQUIVALENT CIRCUITS; IMPEDANCE; MICROSTRUCTURE; NITRIC OXIDE; SENSITIVITY; SPECTROSCOPY

Citation Formats

Woo, L Y, Martin, L P, Glass, R S, Wang, W, Jung, S, Gorte, R J, Murray, E P, Novak, R F, and Visser, J H. Effect of Electrode Composition and Microstructure on Impedancemetric Nitric Oxide Sensors based on YSZ Electrolyte. United States: N. p., 2007. Web.
Woo, L Y, Martin, L P, Glass, R S, Wang, W, Jung, S, Gorte, R J, Murray, E P, Novak, R F, & Visser, J H. Effect of Electrode Composition and Microstructure on Impedancemetric Nitric Oxide Sensors based on YSZ Electrolyte. United States.
Woo, L Y, Martin, L P, Glass, R S, Wang, W, Jung, S, Gorte, R J, Murray, E P, Novak, R F, and Visser, J H. Mon . "Effect of Electrode Composition and Microstructure on Impedancemetric Nitric Oxide Sensors based on YSZ Electrolyte". United States. doi:. https://www.osti.gov/servlets/purl/926046.
@article{osti_926046,
title = {Effect of Electrode Composition and Microstructure on Impedancemetric Nitric Oxide Sensors based on YSZ Electrolyte},
author = {Woo, L Y and Martin, L P and Glass, R S and Wang, W and Jung, S and Gorte, R J and Murray, E P and Novak, R F and Visser, J H},
abstractNote = {The role of metal (Au, Pt, and Ag) electrodes in YSZ electrolyte-based impedancemetric nitric oxide (NO) sensors is investigated using impedance spectroscopy and equivalent circuit analysis. The test cell consists of a rectangular block of porous YSZ with two metal wire loop electrodes, both exposed to the same atmosphere. Of the electrode materials, only Au was sensitive to changes in NO concentration. The impedance behavior of porous Au electrodes in a slightly different configuration was compared with dense Au electrodes and was also insensitive to NO. Ag showed no sensitivity to either O{sub 2} or NO, and the measured impedances occurred at frequencies > 10 kHz, which are typically associated with ionic conduction in YSZ. Pt and porous Au showed sensitivity to O{sub 2}, which was quantified using power-law exponents that suggest electrochemical rate-determining mechanisms occurring at the triple phase boundary. The behavior of the dense Au suggests different rate-determining processes (e.g., diffusion or adsorption) for the O{sub 2} reaction. Although the exact mechanism is not determined, the composition and microstructure of the metal electrode seem to alter the rate-limiting step of the interfering O{sub 2} reaction. Impedance behavior of the O{sub 2} reaction that is limited by processes occurring away from the triple phase boundary may be crucial for impedancemetric NO sensing.},
doi = {},
journal = {Journal of the Electrochemical Society, vol. 155, no. 1, January 1, 2008, J32-J40},
number = 1,
volume = 155,
place = {United States},
year = {Mon Apr 02 00:00:00 EDT 2007},
month = {Mon Apr 02 00:00:00 EDT 2007}
}
  • An impedancemetric method for NO{sub x} sensing using an yttria-stabilized zirconia (YSZ) based electrochemical cell is described. The sensor cell consists of a planar YSZ electrolyte and two identical YSZ/Cr{sub 2}O{sub 3} composite electrodes exposed to the test gas. The sensor response to a sinusoidal ac signal applied between the two electrodes is measured via two parameters calculated from the complex impedance, the modulus |Z| and phase angle {Theta}. While either of these parameters can be correlated to the NO{sub x} concentration in the test gas, {Theta} was found to provide a more robust metric than |Z|. At frequencies belowmore » approximately 100 Hz, {Theta} is sensitive to both the NO{sub x} and O{sub 2} concentrations. At higher frequencies, {Theta} is predominantly affected by the O{sub 2} concentration. A dual frequency measurement is demonstrated to compensate for changes in the O{sub 2} background between 2 and 18.9%. Excellent sensor performance is obtained for NO{sub x} concentrations in the range of 8-50 ppm in background. An equivalent circuit model was used to extract fitting parameters from the impedance spectra for a preliminary analysis of NO{sub x} sensing mechanisms.« less
  • Solid-state electrochemical sensors using two different sensing electrode compositions, gold and strontium-doped lanthanum manganite (LSM), were evaluated for gas phase sensing of NO{sub x} (NO and NO{sub 2}) using an impedance-metric technique. An asymmetric cell design utilizing porous YSZ electrolyte exposed both electrodes to the test gas (i.e., no reference gas). Sensitivity to less than 5 ppm NO and response/recovery times (10-90%) less than 10 s were demonstrated. Using an LSM sensing electrode, virtual identical sensitivity towards NO and NO{sub 2} was obtained, indicating that the equilibrium gas concentration was measured by the sensing electrode. In contrast, for cells employingmore » a gold sensing electrode the NO{sub x} sensitivity varied depending on the cell design: increasing the amount of porous YSZ electrolyte on the sensor surface produced higher NO{sub 2} sensitivity compared to NO. In order to achieve comparable sensitivity for both NO and NO{sub 2}, the cell with the LSM sensing electrode required operation at a lower temperature (575 C) than the cell with the gold sensing electrode (650 C). The role of surface reactions are proposed to explain the differences in NO and NO{sub 2} selectivity using the two different electrode materials.« less
  • This paper reports that in order to make clear the relationship between the microstructure of the porous oxide layer and electrochemical properties of air electrodes of solid oxide fuel cells, air/porous oxide/yttria stabilized zirconia, complex-impedance and cathodic polarization were measured on the air/La{sub 0.6}Ca{sub 0.4}MnO{sub 3}/YSZ electrodes at 900-1000{degrees} C with the porous La{sub 0.6}Ca{sub 0.4}MnO{sub 3} layers of different morphology prepared by different method and different firing temperatures. From the SEM images of the cross section of the interface, the length of the air/La{sub 0.6}Ca{sub 0.4}MnO{sub 3}/YSZ triple-phase boundary and the area of the closely contacted La{sub 0.6}Ca{sub 0.4}MnO{submore » 3}-particles/YSZ interface were estimated. It was shown that the reaction rate was essentially proportional to the length of the triple-phase boundary, while the electrode capacitance was largely proportional to the closely contact area.« less
  • A planar thin-film solid oxide fuel cell has been fabricated with an inexpensive, scalable, technique involving colloidal deposition of yttria-stabilized zirconia (YSZ) films on porous NiO-YSZ substrates, yielding solid oxide fuel cells capable of exceptional power density at operating temperatures of 700 to 800 C. The thickness of the YSZ film deposited onto the porous substrate is approximately 10 {micro}m after sintering, and is well bonded to the NiO/YSZ substrate. Ni-YSZ/YSZ/LSM cells built with this technique have exhibited theoretical open-circuit potentials (OCPs), high current densities, and exceptionally good power densities of over 1900 mW/cm{sup 2} at 800 C. Electrochemical characterizationmore » of the cells indicates negligible losses across the Ni-YSZ/YSZ interface and minor polarization of the fuel electrode. Thin-film cells have been tested for long periods of time (over 700 h) and have been thermally cycled from 650 to 800 C while demonstrating excellent stability over time.« less