NO_x SENSORS BASED ON INTERFACING NANO-SIZED LaFeO_3 PEROVSKITE-TYPE OXIDE AND IONIC CONDUCTORS

摘要

Electrochemical NO_x sensors based on coupling different ionic conductors with perovskite-type LaFeO_3 as auxiliary phase were prepared. The ionic conductors used were yttria-stabilized zirconia (YSZ) that is an oxygen ion conductor and NASICON whose charge carriers are sodium ions. LaFeO_3 is a p-type semiconducting oxide and has been chosen as stable auxiliary phase because of its sensing properties to NO_2. Thick films of LaFeO_3 powders were deposited using a screen printing oil on one side of the solid electrolyte pellets, using powders having different grain sizes. The obtained sensors were wholly exposed to the same atmosphere. Electromotive force (EMF), polarization curves and amperometric measurements were performed in air and at different concentrations of NO_2 in air, at selected temperatures. Quite stable EMF values and fast response times have been obtained. The NO_2 response was much larger when powders with nano-sized grains were used for the preparation of the electrodes. From polarization curves all sensors show a non linear behavior. To better understand the role played by the electrolyte/electrode interface, electrochemical impedance spectroscopy (EIS) measurements were also performed.