Electrochemical solid electrolyte gas sensors — hydrocarbon and NOx analysis in exhaust gases |
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Authors: | U Guth J Zosel |
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Institution: | 1. Meinsberg Kurt-Schwabe-Research Institute, Fabrikstra?e 69, D-04720, Ziegra-Knobelsdorf, Germany 2. Dresden University of Technology, D-01062, Dresden, Germany
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Abstract: | For the in situ measurement of the free oxygen concentration and the equilibrium oxygen partial pressure oxygen sensors based
on zirconia solid electrolytes are widely used in order to monitor and control technical high temperature processes. Similarly
combustibles (HC, CO) and NOx can be determined in non equilibrated oxygen containing gas mixtures of exhausts by mixed potential sensors and amperometric
solid electrolyte sensors. It is expected that their long-term stability is similar to that of oxygen sensors. In both cases
the electrode material with the desired electrochemical and catalytic properties is the key component. Different electrode
materials made of perovskites (La1-xSrxCr1-yGayO3-δ) and composites (Au/Metal oxide) were investigated in different combustibles including CO, C3H6/8, C7H8 and CH4. The response behaviour of mixed potential sensors is determined by the catalytic activity of the measuring electrode, which
is closely connected with the defect structure and depends on the measuring conditions. Furthermore the electrode response
can be understood by electrokinetic data. Gas symmetrical mixed potential sensors with electrodes made of Au/Nb2O5 composites show maximum sensitivity. By using Ptreference electrodes without equilibrium behaviour the sensors are applicable
in lean and rich mixtures as well. In the amperometric sensor mode the consecutive determination of oxygen and NOx or combustibles at two working electrodes is possible. The catalytic activity of the oxygen pumping electrode should be low
in order to avoid the decomposition of NO and HC respectively. Alternatively, the electrochemical reduction of NO can be performed
at a single working electrode, made of materials with improved NO selectivity, without the previous reduction of oxygen.
Paper presented at th 8th EuroConference on Ionics, Ixia, Rhodos, Greece, Sept. 15–21, 2002. |
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