Improving NO[sub 2] Sensitivity by Adding WO[sub 3] during Processing of NiO Sensing-Electrode of Mixed-Potential-Type Zirconia-Based Sensor

A planar sensor was fabricated by using an yttria-stabilized zirconia plate and NiO-based sensing electrode (SE). The improvement in sensing characteristic of mixed-potential-type planar sensor was examined by the addition of various metal oxides to NiO-SE. Among the metal-oxide additives tested, was found to give a significant enhancement in sensitivity. In addition, this enhancement was maximum when the initial content in the NiO-based paste before sintering was . The sensitivity (Δ electromotive force) to was as high as about for the sensor using the -added NiO-SE at under the wet condition (containing ). The sensitivity of this sensor was still even down to at . The sensitivity was found to be invariant to different concentrations of and in the examined range of 5–15 and 5–20 , respectively. It is speculated that the modification of morphology of the NiO-SE layer by the addition of is the main contributing factor for the improved sensitivity of the sensor.