D2.1 - Potential-Type Sulfur Dioxide Planar Gas Sensor for High Temperature Application

SENSOR+TEST Conferences 2011
2011-06-07 - 2011-06-09
Proceedings SENSOR 2011
D2 - High Temperature Sensors II
R. Moos, G. Hagen, D. Schönauer, U. Röder-Roith - Universität Bayreuth (Germany), N. Izu - National Institute of Advanced Industrial Science and Technology (AIST), Nagoya (Japan)
538 - 542


Today, coal is a very important fuel. Besides renewable energies, it will continue to play an important role through the 21st century. Coal, however, faces significant environmental challenges, since exhaust gas from coal combustion contains limited emissions such as SO2, NOx, etc. For emission control purposes, it would be very helpful to develop a sensor for monitoring SO2 directly in the hot exhaust. For the SO2 sensor, a very stable material is needed. Besides others, we focused on V2O5/WO3/TiO2 (VWT) due to its well-known properties as a selective catalytic reduction (SCR) catalyst in harsh environments. In this study, we investigated the response properties towards SO2 and on the cross sensitivity for a planar-type sensor with Nasicon as an electrolyte and Au/VWT as a sensing electrode.
First, a solid electrolyte layer (Nasicon) was screen-printed. Then, two porous gold electrodes were screen-printed. Afterwards, one electrode was covered by an additional porous catalytic active film (VWT) which included 1.5 or 3.0 wt% V2O5. The voltage between two gold electrodes was measured, serving as the sensor signal. The measurements were conducted at temperatures from 300 to 600 °C. Typically, air was used as a base gas.
Above 500 °C, the voltage is stable and the measured voltage increases with increasing SO2 concentrations in the SO2 range from 20 to 200 ppm. The slope of the line in a semi-logarithmic plot increases with increasing temperature in the range of 20 - 200 ppm. The sensitivity of the sensor with 1.5 or 3.0 wt%V2O5 is 75-85 mV/decade at 600 °C. This sensitivity would be suitable for high temperature applications. In repeated measurements, an offset shift is observed but the slope remains almost the same. This problem may be related to a secondary effect that occurs when the SO2 concentration changes from 0 to 20 ppm. In high SO2 concentrations (200 - 5000 ppm), the slope decreases. This means that a kind of saturation of the signal occurs at high SO2 concentrations. The sensors show only little or no response to CO2, CO, H2O, C3H8 and NO, and only H2 and NH3lead to marked effects.
It seems that the sensors may be selective enough for in-situ waste gas monitoring. However, the long-term signal stability needs to be further investigated.