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Bismuth ruthenate pyrochlore (Bi2 Ru2 O7: BRO) was tested as a cathode in several bismuth oxide-based electrolyte cells. Erbium oxide stabilized bismuth oxide (ESB) (Bi2 O3) 0.8 (Er2 O3) 0.2, Bi2 V0.9 Me0.1 O5.35 (BIMEVOX10, Me=Co, Cu, Zn), and Bi2 Ru2 O7 (BRO) were synthesized via solid- state reaction. ESB and BIMEVOX powders were pressed and sintered into dense pellets while BRO was deposited and sintered as porous electrodes onto ESB and BIMEVOX dense pellet surfaces. Morphologies and phases of the materials were characterized by field emission scanning electron microscope and X-ray diffraction, respectively. Electrochemical performances of BRO/ESB and BRO/BIMEVOX symmetric cells were tested using electrochemical impedance spectroscopy at 200-700°C in air. High polarization for BRO/BIMEVOX cells was observed. In contrast, BRO/ESB cells showed promising low polarization behavior. Different electrochemical performances of BRO electrodes, with ESB or BIMEVOX, indicated that the phases formed at the electrode/electrolyte interface dominated the cell polarization process for BRO/BIMEVOX cells.The Electrochemical Society © 2006 The Electrochemical Society. Index Keywords: Bismuth compounds; Electrolytes; Polarization; Porous materials; Reaction kinetics; Scanning electron microscopy; Sintering; Synthesis (chemical); X ray diffraction; Bismuth ruthenate pyrochlore; Electrochemical performances; Erbium oxide; Field emission scanning electron microscope

The non-Nernstian behavior of zirconia-based electrochemical NOx and CO sensors with various semiconducting oxides as sensing electrodes was extensively studied in the temperature range 450-700°C. Both pellets and tape-cast layers of yttriastabilized zirconia were used for the fabrication of the sensors. It was found that the gas-sensing mechanism of the sensors cannot be explained always by the mixed potential theory. When semiconducting oxides are used as sensing electrodes, the semiconductor sensing mechanism and the adsorption-desorption behavior of the different oxides dominate the sensor response if both metal and oxide are exposed to the same environment.

Electrochemical sensors based on yttria-stabilized zirconia (YSZ) with WO3 as a sensing electrode were fabricated using either Pt or Au electrodes. The sensors were studied in the temperature range 500-700°C in the presence of different concentrations (300-1000 ppm) of NO2 and CO in air. The response to NO2 was very stable with fast response time (within 20 s). The best sensitivity was observed at 600 and 650°C using Pt and Au electrodes, respectively. At all temperatures investigated a cross sensitivity to CO gas was also noticed. The response to CO was decreased using Au electrodes. The role played by WO3 as a sensing electrode was investigated. © 2003 The Electrochemical Society. All rights reserved.

Electrochemical NOx sensors based on coupling different ionic conductors with perovskite-type LaFeO3 as auxiliary phase were prepared. The ionic conductors used were yttria-stabilized zirconia that is an oxygen ion conductor and sodium superionic conductor whose charge carriers are sodium ions. Thick films of LaFeO3 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 NO2 in air, at selected temperatures. Quite stable emf values and fast response times were obtained. The NO2 response was much larger when powders with nanosized grains were used for the preparation of the electrodes. From polarization curves, all sensors showed a nonlinear behavior. The role played by the electrolyte/electrode interface was determined by electrochemical impedance spectroscopy measurements; exposure to NO2 did not affect the bulk but only the electrolyte/electrode interface. © 2001 The Electrochemical Society. [DOI: 10.1149/1.1386921] All rights reserved.

Electrochemical sensors for Volatile Organic Compound (VOCs) based on commercial YSZ layers were fabricated using Pt as reference electrode and SmFeO3 perovskite oxide as a sensing electrode, both exposed to the same gas environment. Pt was sputtered on YSZ layers while SmFeO3 p-type semiconducting oxide was deposited by electrophoretic deposition (EPD). Nanometric SmFeO3 oxide powders were selected because they have already shown good sensing performance in semiconducting sensors for oxidizing gases such as NO2 and ozone, and reducing gases, such as VOCs. Potentiometric measurements were performed under exposure to different concentrations of VOCs such as: methyl ethyl ketone (MEK), ethanol (EtOH) and acetic acid (AA). The best gas sensing response was obtained at 400°C.