NOx detection using the electrolysis of water vapor in a YSZ cell - Part II. Electrochemical oxygen pump

The detection of NO in the presence of excess oxygen has been carried out using four electrochemical cells, Pt\YSZ\Pt, which serve as an electrochemical pumping cell, an electrolysis cell and two oxygen sensors, respectively. Their operation temperature was 800 degrees C. A mixture of 0-2500 ppm NO, 1-7% oxygen, 3-10% water vapor and 0-10% carbon dioxide in argon was used as a sample gas. At the electrochemical pumping cell, oxygen in the sample gas was removed down to a constant concentration of 1800 ppm, which was monitored by the oxygen sensor. At the electrolysis cell, water vapor in the sample gas was electrolyzed, and the resulting hydrogen reacted with NO in the sample gas. Finally, the sample gas was fed into another oxygen sensor. Two potentiometric and amperometric methods were adopted to detect NO. In the potentiometric method, the EMF value of the oxygen sensor decreased with increasing NO concentration. In the amperometric method, the current applied to the electrolysis cell was proportional to the concentration of NO. Additionally, the influences of the coexisting oxygen, water vapor and carbon dioxide in the sample gas on the detection of NO were investigated in detail. (C) 1998 Elsevier Science B.V. All rights reserved.