Mixed-potential type N₂O sensor using stabilized zirconia- and SnO₂-based sensing electrode

A stabilized zirconia-based electrochemical device attached with an oxide electrode was developed for monitoring nitrous oxide (N₂O) in air at elevated temperatures. Among the 11 kinds of monoxides tested for a tubular zirconia device, SnO₂ was found to exhibit the best sensing electrode properties, giving a relatively high sensitivity to N₂O in air at 475°C. The electromotive force (emf) value of the device was almost linear to the logarithm of N₂O concentration in the range of 50-200 ppm. The addition of a foreign oxide (e.g. Bi₂O₃ and Sm₂O₃) to SnO₂ was effective to improve the N₂O sensitivity. Especially the element using Sm₂O₃ (0.5 wt.%)-SnO₂ sensing electrode exhibited the N₂O sensitivity about 1.5 times as high as that using the pure SnO₂ electrode, allowing to detect about 35 ppm N₂O in air. On the basis of the measurements of anodic and cathodic polarization curves, the sensing mechanism was confirmed to involve a mixed potential at the sensing electrode.