Response behavior of perovskites and Au/oxide composites as HC-electrodes in different combustibles J. Zosel a, * , R. Mqller a , V. Vashook b , U. Guth a,b a Kurt-Schwabe-Institute for Measuring and Sensor Technology Meinsberg, Fabrikstrage 69, D-04720, Ziegra-Knobelsdorf, Germany b Institute of Physical Chemistry and Electrochemistry, Dresden University of Technology, D-01062 Dresden, Germany Received 29 April 2003; accepted 13 January 2004 Abstract Mixed potential solid electrolyte sensors are suited for the in situ measurement of hydrocarbons (HCs) in exhausts with respect to their potential for long-term stability, miniaturization and low-cost solutions. Their response behavior in nonequilibrated oxygen containing gas mixtures is mainly determined by the catalytic activity of the measuring electrode and depends strongly on preparation and measuring conditions. In this work, the sensitivity of electrodes made of perovskites (La 1x Sr x Cr 1y Ga y O 3d ) and composites (Au/MeO) was investigated in different combustibles including CO, C 3 H 6/8 ,C 7 H 8 , and CH 4 . Gas symmetrical mixed potential sensors were produced and characterized with electrodes made of Au/Nb 2 O 5 composites, which show maximum sensitivity. By using platinum (Pt)-reference electrodes without equilibrium behavior, the sensors are applicable in lean and rich mixtures as well. D 2004 Elsevier B.V. All rights reserved. PACS: 07.07.Df; 68.10.Jy; 81.70.Yp; 82.65.Yh Keywords: Mixed potential HC-sensor; Yttria-stabilized zirconia (YSZ); Pt-reference electrode; Gas symmetrical sensor 1. Introduction The in situ measurement of hydrocarbons (HCs) in exhausts as an effective way of catalyst monitoring and combustion control is based on the availability of reliable, selective, low cost sensors working at temperatures of up to 800 8C. Mixed potential solid electrolyte sensors fulfill these requirements, if electrode materials with high sensi- tivity and appropriate long-term stability are available. To improve these sensors, a variety of materials have been prepared and investigated as HC-electrodes until now [1–5]. In earlier works [1,6], relations between electrode response and catalytic activity regarding HC-combustion were found. The aim of this work was the comparison between the response of HC-sensitive electrodes in potentiometric cells with air references and the potential behavior of sensors with both electrodes in the measuring gas (gas symmetrical sensors) in different combustibles. 2. Experimental The perovskites prepared with the oxide method were mixed with an organic binder after sintering and milling to produce printable pastes. The composite pastes were mixed from commercially available Au pastes and oxide pastes. The following systems were prepared: – La 1x Sr x Cr 1y Ga y O 3d with x =(0...0.02) and y = (0...0.3) – Au/MeO-composites with 20 wt.% of Ga 2 O 3 , Nb 2 O 5 , and In 2 O 3 as MeO 0167-2738/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.ssi.2004.01.074 * Corresponding author. Tel.: +49 34327/608 102; fax: +49 34327/608 131. E-mail address: zosel@ksi-meinsberg.de (J. Zosel). Solid State Ionics 175 (2004) 531 – 533 www.elsevier.com/locate/ssi