Potentiometric Sensor Based on Chromium Vanadate Sensing Electrode for High Temperature Ammonia Detection

Abstract

Mixed-potential sensors using CrVO4 sensing electrodes were prepared for monitoring ammonia at high temperatures. NH3 sensitivity for the sensors sintered at 800 °C, 850 °C and 900 °C were −56.5, −75.0 and −32.1 mV/decade respectively for the NH3 above 10 ppm. High sintering temperature strengthens the bond of electrode and electrolyte, thus increasing the amount of TPB sites. Thinner electrode weakens the heterogeneous catalytic consumption of NH3. More reaction sites combined with higher NH3 concentration result in greater sensitivity for 850 °C-sintered sensor. 900 °C sintering leads to decomposition of CrVO4 into Cr2O3 and V2O5, which exhibits low NH3 sensitivity. In operating temperature range of 500 °C–600 °C, NH3 detection limit is 2 ppm. The sensor shows the biggest responses at 500 °C, but the optimum NH3 sensitivity of −75.0 mV/decade was obtained at 550 °C for the concentrations higher than 10 ppm. For the oxygen of 4–10 vol %, response is less affected by the change of oxygen content, the influence of water vapor with content of 5–6 vol % could also be ignored. The characteristics of high NH3 selectivity, sensitivity, long-term stability and anti-interference performances indicate that it is meaningful to use CrVO4 for ammonia detection in exhaust.