Abstract
The influence of electrode configuration on the impedancemetric response of nitric oxide (NO) gas sensors was investigated for solid electrochemical cells [Au/yttria-stabilized zirconia (YSZ)/Au)]. Fabrication of the sensors was carried out at 1050 °C in order to establish a porous YSZ electrolyte that enabled gas diffusion. Two electrode configurations were studied where Au wire electrodes were either embedded within or wrapped around the YSZ electrolyte. The electrical response of the sensors was collected via impedance spectroscopy under various operating conditions where gas concentrations ranged from 0 to 100 ppm NO and 1%–18% O2 at temperatures varying from 600 to 700 °C. Gas diffusion appeared to be a rate-limiting mechanism in sensors where the electrode configuration resulted in longer diffusion pathways. The temperature dependence of the NO sensors studied was independent of the electrode configuration. Analysis of the impedance data, along with equivalent circuit modeling indicated the electrode configuration of the sensor effected gas and ionic transport pathways, capacitance behavior, and NO sensitivity.
Highlights
Advancements in diesel fuel and engine technology continue to provide greater fuel efficiency and lower NOx (i.e., NO and NO2) emissions for diesel powered vehicles
Impedance measurements were carried out in order to determine the effect of electrode configuration on the electrical response of the NOx sensors
As for the EC1 sensors, the greater distance between the wire loop and embedded electrodes may have caused oxygen transport to occur over a longer time period such that the rate of oxygen arriving at the Au/Yttria-stablized ziriconia (YSZ) interface coincided more closely with triple phase boundary (TPB) reaction rates
Summary
Advancements in diesel fuel and engine technology continue to provide greater fuel efficiency and lower NOx (i.e., NO and NO2) emissions for diesel powered vehicles. Agency (EPA) as studies have shown that even concentrations as low as 20 ppm can be harmful to the environment and human health [1,2]. To address this issue, various diesel aftertreatment systems including, lean NOx traps, selective catalytic reduction, fuel regeneration and diesel exhaust fluid (i.e., urea), have been implemented to reduce NOx to non-toxic gases [3,4]. It is expected that the lower emissions resulting from further development in diesel engine technology, as well as increasingly stringent EPA standards, will require sensors that are capable of monitoring NOx concentrations as low as 1 ppm. The influence of electrode configuration on gas and ionic transport pathways, reactions at the electrode/electrolyte interface, and rate-limiting mechanisms is discussed with respect to the sensor response to NO
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