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Impedance Analysis of Electrochemical NOx Sensor Using a Au/Yttria-Stabilized Zirconia (YSZ)/Au cell

Published online by Cambridge University Press:  26 February 2011

Leta Y. Woo ,
L. Peter Martin ,
Robert S. Glass  and
Raymond J. Gorte
Leta Y. Woo
Affiliation:
[email protected], Lawrence Livermore National Laboratory, Energy and Environment Directorate, P.O. Box 808, L-367, Livermore, CA, 94551-9900, United States
L. Peter Martin
Affiliation:
[email protected], Lawrence Livermore National Laboratory, Energy and Environment Directorate, Livermore, CA, 94550, United States
Robert S. Glass
Affiliation:
[email protected], Lawrence Livermore National Laboratory, Energy and Environment Directorate, Livermore, CA, 94550, United States
Raymond J. Gorte
Affiliation:
[email protected], University of Pennsylvania, Chemical and Biomolecular Engineering, Philadelphia, PA, 19104, United States
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Abstract

An electrochemical cell employing a YSZ electrolyte and two Au electrodes was utilized as a model system for investigating the mechanisms responsible for impedancemetric NOx (NO and NO2) sensing. The cell consists of two dense Au electrodes on top of a porous/dense YSZ bilayer structure (with the additional porous layer present only under the Au electrodes). Both electrodes were co-located on the same side of the cell, resulting in an in-plane geometry for the current path. The porous YSZ appears to extend the triple phase boundary and allows for enhanced NOx sensing performance, although the exact role of the porous layer is not completely understood. Impedance data were obtained over the frequency range of 0.1 Hz to 1 MHz, and over a range of oxygen (2 to 18.9%) and NOx (10 to 100 ppm) concentrations, and temperatures (600 to 700 °C). Data were fit with an equivalent circuit, and the values of the circuit elements were obtained for different concentrations and temperatures. Changes in a single low-frequency arc were found to correlate with concentration changes, and to be temperature dependent. In the absence of NOx , the effect of O2 on the low-frequency resistance could be described by a power law, and the temperature dependence described by a single apparent activation energy at all O2 concentrations. When both O2 and NOx were present, however, the power law exponent varied as a function of both temperature and concentration, and the apparent activation energy also showed dual dependence. Adsorption mechanisms are discussed as possibilities for the rate-limiting steps.

Keywords

sensorelectrical propertiesionic conductor
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 972: Symposium AA – Solid-State Ionics—2006 , 2006 , 0972-AA12-02
Copyright
Copyright © Materials Research Society 2007

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