Non-Nernstian planar sensors based on YSZ with a Nb2O5 electrode

The discussion about the sensing mechanism of non-Nernstian electrochemical gas sensors with a semiconducting sensing electrode is still open. This work reports a study of the influence of the metallic electrode under the semiconducting metal oxide, Nb2O5, on the sensor response. Planar sensors based on tape-cast YSZ layers were fabricated. Two Pt or Au finger electrodes were deposited on one side of the layers. One of the electrodes was covered with a Nb2O5 thick film. The response to CO was studied performing electromotive force (EMF) measurements in the 450–650 °C temperature range. In order to better understand the sensing mechanism, the electrical measurements were correlated to catalytic measurements performed on both electrodes. With no catalytic electrodes, the adsorption-Fermi level related mechanism seems to prevail, while in the case of sensors with Nb2O5|Pt|YSZ electrode, the mixed potential theory is more adapted to explain the results.