Ammonia Sensing Performance of Manganese Vanadate at High Temperature

Abstract

Based on the polyvalent characteristics and excellent catalytic performances of manganese and vanadium, potentiometric gas sensor using MnV₂O₆ sensing electrode was fabricated for NH₃ detection at high temperatures. NH₃ sensitivity of the sensors sintered at 700 °C, 750 °C and 800 °C were −52.4, −60.0 and −39.1 mV/decade respectively, and the detection limit reaches 2 ppm at 550 °C. 700 °C-sintered sensor displays the slowest response rate, and sample sintered at 800 °C shows the lowest and unstable responses. Excessive temperature promotes the destruction of electrode microstructure, thus leads to the deterioration of sensor’s sensitivity. For NH₃ below 40 ppm, sensor attached with MnV₂O₆ electrode has the highest responses and slowest recovery rate at operating temperature of 500 °C, and presents the lowest signal and fastest recovery at 600 °C. 550 °C is considered the optimal operating temperature based on high sensitivity and shortest response time. Cross sensitivity of MnV₂O₆ to other oxidizing/reducing gases is much lower than NH₃, and it shows good anti-interference ability to oxygen/vapor content change in certain range. Polarization curve showed that the reason for high NH₃ selectivity was mainly due to high electrochemical catalytic activity of MnV₂O₆ to NH₃, and electrochemical impedance spectroscopy test proved that sensing electrode played a leading role compared with reference electrode in response process.