Laure Chevallier

Propene Detection at High Temperatures Using Highly Sensitive Non-Nernstian Electrochemical Sensors Based on Nb and Ta Oxides

Non-Nernstian electrochemical gas sensors using yttria-stabilized zirconia (YSZ) as an electrolyte offer a simple and inexpensive way of measuring combustion gas emissions at high temperatures. This work reports the development of potentiometric planar sensors for the specific detection of propene at high temperatures. Nb 2 O 5 and Ta 2 O 5 powders were investigated as sensing electrodes due to their unique catalytic properties toward the decomposition of hydrocarbons. Three Pt|YSZ|metal oxide (MOx) planar electrochemical cells were prepared, based on commercial tape-cast YSZ layers, using Nb 2 O 5 , Ta 2 O 5 , and a Nb 2 O 5 :Ta 2 O 5 mixture in 1:1 weight ratio as MOx sensing electrodes, and their sensing performance was compared. All the sensors showed outstanding responses to 1000 ppm of propene in air and propene sensitivities at 700°C, being -214 mV and -190 mV/dec, respectively, the largest for Ta 2 O 5 electrode-based sensors. However, the sensors using the Nb 2 O 5 :Ta 2 O 5 mixture electrode showed the best performance in terms of compromising selectivity and stability with keeping large response and sensitivity values.

Non-Nernstian Electrochemical Sensors with a Nb2O5 Sensing Electrode for Engine Exhaust Monitoring

Non-Nernstian electrochemical planar sensors with a Pt electrode and a sensing electrode made using Nb2O5 powders were fabricated. Two cell configurations were compared, one with and the other without Pt paste under the metal oxide electrode. The sensors were tested both in laboratory and in situ i.e., downstream of a three-way catalytic converter of a FIAT fire 1242 c.c. spark ignition engine . The best sensing performance, both in the laboratory and at the engine bench, was obtained for the yttriastabilized zirconia Pt YSZ Nb2O5 cell, without Pt below the oxide electrode. For this sensor configuration, very large electromotive force response values were obtained for hydrocarbon exposure both in the laboratory and in field tests, even at temperatures as large as 700°C.

Non-Nernstian Planar Sensors Based on YSZ with an Nb2O5 Electrode: Discussion on Sensing Mechanism

Solid electrolyte based sensors have been widely studied for the detection of CO/HC and NOx at high temperature. Nevertheless, the discussion about the sensing mechanism of non-nernstian electrochemical gas sensors, with a semiconducting sensing electrode, is still open. In this work, a study of the influence of the metallic electrode under the semiconducting metal oxide Nb2O5 on the sensor response was performed. Planar sensors based on tape-cast YSZ layers were fabricated. Two Pt or Au finger electrodes were deposited in a parallel arrangement on a single side of YSZ. One of these electrodes was covered with Nb2O5 thick film. In order to better understand the sensing mechanism, the electrical measurements were correlated with catalytic measurements performed on both sensing and reference electrodes.

Fabrication of Proton Conducting Solid Oxide Fuel Cells by using Electrophoretic Deposition

Anode-supported proton conducting solid oxide fuel cells (SOFCs) were fabricated by using electrophoretic deposition (EPD) for the electrolyte film deposition. BaCe0.9Y0.1O3-δ (BCY10) thick films were deposited on NiO-BCY10 substrates. The influence of the EPD parameters on the microstructure and electrical properties of BCY10 thick films was investigated. The anode substrates and electrolyte deposits were co-sintered at 1550 degrees C for 2 h to obtain a dense electrolyte thick film, while keeping a suitable porosity in the anode. Innovative composites with La0.8Sr0.2Co0.8Fe0.2O3 (LSCF)-BaCe0.9Yb0.1O3-δ (10YbBC) composition were used as cathode materials. Prototype SOFCs were prepared by depositing the composite cathode on the co-sintered half cells. Fuel cell tests and electrochemical impedance spectroscopy (EIS) measurements were performed in the 550–700 degrees C temperature range. The maximum power density of 296 mW cm-2 was achieved at 700 degrees C.