Takafumi Oshima

NOx detection using the electrolysis of water vapour in a YSZ cell: Part I. NOx detection

Abstract The reaction of NO with the hydrogen formed by electrolyzing water vapour in a YSZ cell has been applied to detect NO with output signal of magnitude in millivolt or milliampere. The experimental apparatus consisted of two YSZ cells, Pt|YSZ|Pt, which served as an electrolysis cell and an oxygen sensor, respectively. A mixture of 0–3000 ppm NO and 3% H 2 O in argon was successively fed to the two cells at 800°C. In the upstream cell, the hydrogen formed by electrolyzing water vapour in the sample gas reacted with NO in the sample gas. In the downstream cell, the electromotive force (EMF) value was measured using air as a reference gas. The EMF value of the oxygen sensor was used as a sensor signal, when a current of 6.7 mA was applied to the electrolysis cell. The EMF signal decreased with increasing NO concentration in the sample gas. Furthermore, the current applied to the electrolysis cell was used as another sensor signal, when the EMF value of the oxygen sensor was held at 700 mV. The current signal increased with increasing NO concentration in the sample gas.

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

Abstract 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°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.