Sensors and Actuators B 123 (2007) 929–936
High temperature amperometric total NOxsensors
with platinum-loaded zeolite Y electrodes
Jiun-Chan Yang, Prabir K. Dutta∗
Department of Chemistry, The Ohio State University, Columbus, OH 43210-1185, USA
Received 20 July 2006; received in revised form 30 October 2006; accepted 31 October 2006
Available online 4 December 2006
An amperometic total-NOxsensor that integrates a Pt-loaded zeolite Y (PtY) catalyst for NOxequilibration with electrochemical oxidation of
NO on an yttria-stabilized zirconia (YSZ) electrolyte is described in this paper. PtY is found to be an effective catalyst for equilibrating mixtures
of NO, O2and NO2at temperatures in excess of 400◦C. By applying a low anodic potential of 80mV, the NO in the NOxequilibrated mixture can
be oxidized at a Pt working electrode on the YSZ electrolyte at 500◦C. The current thus generated provides a measure of the total NOxin the gas
stream and is the basis of the sensing measurements in this study. The PtY can be held separate from the YSZ or coated onto the YSZ as a film, the
latter being more appropriate for the practical embodiment of this design. We demonstrate that this sensor exhibits total-NOxdetection capability,
a low NOxdetection limit (<1ppm), high NOxselectivity relative to CO and oxygen, and linear dependence on NOxconcentration.
© 2006 Elsevier B.V. All rights reserved.
Keywords: Combustion monitoring; Exhaust analysis; Harsh environment sensors; Electrochemical sensors
Nitrogen oxides are emitted from high temperature com-
bustion processes, including transportation vehicles and power
plants. Since NOxspecies are considered to be precursors to
urban smog and acid rain, there is considerable regulatory
pressure to reduce NOx emissions. With the availability of
fast response NOx sensors, emissions can be monitored, but
more importantly, optimizing the combustion process via feed-
back control can also reduce emissions. For example, new
automotive engine designs, such as lean-burn gasoline and
on fuel efficiency, but commercialization depends on minimiz-
systems have been developed for such engines with periodic
regeneration . A sensitive, rapid response NOx sensor is
essential for monitoring the concentration of residual NOxand
triggering regeneration processes.
Several types of solid-state NOxsensors have been discussed
in the literature for operation in high temperature combus-
∗Corresponding author. Tel.: +1 614 292 4532; fax: +1 614 292 0462.
E-mail address: firstname.lastname@example.org (P.K. Dutta).
temperature operation (>500◦C) show significant promise .
Potentiometric measurements exploiting the difference of the
extent of NOxequilibration between two electrodes provide a
measure of NOxconcentration [4–6]. Other studies have shown
that NOxdetection can be done in the amperometric mode by
polarizing the working electrode to a constant potential and
ric devices usually contain diffusion barriers and are operated
feature of the diffusion barrier and not significantly influenced
by the aging of the microstructure of the electrode/YSZ inter-
face . Such sensors though lead to poor signal/noise ratios at
Although electrochemical NOxsensors show promise, selec-
tivity is a major limitation. First, the two main components of
nitrogen oxides in combustion environments are NO and NO2,
and sensors need to distinguish between them or provide a total
NOxmeasurement. Second, CO, hydrocarbons, O2and ammo-
NO [1,3,7,9,10] yet NO2can also be an important constituent.
Since NO2tends to get reduced and NO tends to get oxidized,
0925-4005/$ – see front matter © 2006 Elsevier B.V. All rights reserved.
J.-C. Yang, P.K. Dutta / Sensors and Actuators B 123 (2007) 929–936
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Jiun-Chan Yang received his BS degree in 1995 from National Chiao-Tung
University, Hsin Chu, Taiwan, and a MS degree in Chemistry from National
istry at the Ohio State University, where his research is focused on solid-state
electrochemical devices for gas sensing.
Prabir K. Dutta received his PhD degree in Chemistry in 1978 from Princeton
University. After 4 years of industrial research at Exxon Research and Engi-
neering Company, he joined The Ohio State University, where currently he is
the Robert K. Fox Professor and Chairman of the Department of Chemistry. His
research interests are in the area of solid state chemistry and materials science.