Development of Single Chamber Solid Oxide Fuel Cells (SCFC)

International audienceSingle Chamber Solid Oxide Fuel Cells (SCFC) have been prepared using an electrolyte as support (Ce0.9Gd0.1O1.95 named GDC). Anode (Ni-GDC) and different cathodes (Sm0.5Sr0.5CoO3 (SSC), Ba0.5Sr0.5Co0.2Fe0.8O3 (BSCF) and La0.8Sr0.2MnO3 (LSM)) were placed on the same side of the electrolyte. All the electrodes were deposited using screen-printing technology. A gold collector was also deposited on the cathode to decrease the over-potential. The different materials and fuel cell devices were tested under propane/air mixture, after a preliminary treatment under hydrogen to reduce the as-deposited nickel oxide anode. The results show that SSC and BSCF cathodes are not stable in these conditions, leading to a very low open circuit voltage (OCV) of 150 mV. Although LSM material is not the more adequate cathode regarding its high catalytic activity towards hydrocarbon conversion, it has a better chemical stability than SSC and BSCF. Ni-GDC-LSM SCFC devices were elaborated and tested; an OCV of nearly 750 mV could be obtained with maximum power densities around 20 mW cm–2 at 620 °C, under air–propane mixture with C3H8/O2 ratio equal to 0.53

CO detection in H2 reducing atmosphere with mini fuel cell

International audienceA prototype of a miniaturized fuel cell has been studied in order to detect carbon monoxide in hydrogen-rich atmosphere for PEMFC (proton exchange membrane fuel cell) applications. It consists on a single PEMFC (membrane-electrode-assembly supplied by CEA/LITEN) directly fed by the hydrogen-carbon monoxide mixture while the cathode is exposed to ambient air. Experiments have been carried out on a laboratory testing bench with simulated reforming gas. Two working modes have been studied. For low CO concentrations (≤20 ppm), the amperometric mode is suitable but a regeneration in air is necessary to obtain a good reversibility of the sensor response. On the contrary, for higher CO concentrations (250-4000 ppm), a good reversible response is observed without air regenerating by using a potentiometric or quasi-potentiometric mode. Therefore, this prototype of mini fuel cell sensor seems to be convenient for monitoring reformed gases either for low temperature PEMFC which are poisoned by very low traces of CO or for high temperature PEMFC which can operate at higher CO concentrations

Detection of CO in H2-rich gases with a samarium doped ceria (SDC) sensor for fuel cell applications

International audienceAn original sensor has been studied in order to detect low CO concentration in h2-rich atmosphere for pem (protonic exchange membrane) fuel cell applications. The SCD (samarium doped ceria) sensor is a potentiometric sensor working with an electrode dissymmetry Au/Pt. The originality of this sensor is mainly working with the two electrodes in the same atmosphere without a reference cell. The Δ (emf) response, defined by the difference between the emf (electromotive force) value under carrier gas and the emf value under CO, is correlated with the CO concentration. Experiments have been carried out on a laboratory testing bench, either with a large measurement cell equipped with a hot plate and two mobile gold points as electrical contacts or in a small cell with self-heated sensors supplied with a platinum heater on the reverse side of the substrate. Responses to low CO concentrations (0-4000 ppm v/v) in H2-rich gases (5% v/v) varies between 25 and 100 mV, but saturation is observed beyond 400 ppm v/v of CO. In wet atmosphere, the sensitivity is partially reduced but the sensor response remains perfectly usable. At the moment no satisfying model can be used to explain the experimental results. Nevertheless, the performances of these SCD sensors appear sufficiently good to satisfy the fuel cell application

Preconcentration Modeling for the Optimization of a Micro Gas Preconcentrator Applied to Environmental Monitoring.

International audienceThis paper presents the complete modeling of the preconcentration cycle for the optimization of a Micro Gas Preconcentrator applied to atmospheric pollution monitoring. The particularity of this modeling is based on the fact that it includes all equations governing not only the adsorption and desorption phenomena but also the detection phase. Two different approaches based on kinetic equations were used to illustrate the behavior of the Micro Gas Preconcentrator for given experimental conditions. The need of a high adsorption flow and heating rate, a low desorption flow and detection volume is demonstrated through this paper

Suivi de pollution atmosphérique par système multi-capteurs méthode mixte de classification et de détermination d'un indice de pollution..

Cette thèse a pour objectif le développement d un système multi-capteurs de gaz permettant une évaluation en continu et en temps réel des différentes types de pollution atmosphérique en zone urbain, en classifiant notamment les pollutions de type urbaine, photochimique, ou encore liée au trafic. Le projet se base sur l utilisation de différents capteurs de gaz de type semi-conducteur disponibles dans le commerce qui sont intégrés dans un dispositif autonome et portable, afin qu il puisse fonctionner sur site.Dans un premier temps, et en grande partie à Saint-Etienne, différents types de capteurs sont sélectionnés puis leurs performances sont testées sur un banc simulant les atmosphères polluées et développé pour l occasion. Afin de pallier aux problèmes de non répétabilité et de dérive de la ligne de base et de la sensibilité, des procédures de prétraitement de standardisation sont mises au point.Dans un deuxième temps, et en grande partie à Douai, différents sites de tests sont identifiés et leurs historiques de pollution sont étudiés. Plusieurs campagnes en stations de mesure d une semaine, recouvrant les différentes saisons et les différents types de sites, sont alors menées. Il y est collecté conjointement les signaux des capteurs et des analyseurs de gaz réglementés. Des méthodes basées sur les réseaux de neurones sont alors appliquées afin d obtenir conjointement, à partir des signaux des capteurs, une classification parmi 3 types de pollutions (urbaine, trafic et photochimique) ainsi qu un indicateur global de qualité de l air. Ces méthodes utilisent une approche basée sur la logique floue afin d éviter les problèmes d effet de bord.No english abstractST ETIENNE-ENS des Mines (422182304) / SudocSudocFranceF

Detection of oxygen traces in nitrogen and hydrogen-rich atmosphere

International audienceTin oxide sensors are evaluated to detect traces of oxygen in the range 0-100 ppm both in nitrogen and hydrogen (4.5 vol% H2 in N2) atmospheres. In nitrogen, significant relative responses to oxygen are measured at 623 K and 723 K. However, at lower temperature, 523 K, the response strongly decreases. In the presence of hydrogen, on the contrary, interesting responses are measured at 523 K. At higher temperature, 623 K and 723 K, on one hand SnO2 sensors begin to reduce, and on the other hand, oxygen is partly consumed by reaction with hydrogen. Oxygen trace detection (5-100 ppm) is thus only possible in hydrogen atmosphere (4.5 vol% H2) at 523 K

Development of a NOx gas sensor for exhaust

Communication présentée dans la session "Automative Exhaust". Jean-Paul Viricelle préside la session "Automative Exhaust"et participe à ce congrès dans la catégorie "Conférence Invitée".International audienceA high-sensitive sensor for NOx detection based on selective electrochemical reduction of NO2 is proposed. Electrochemical cell consisting of three metallic electrodes and YSZ electrolyte operates under electric polarization and allows selective NO2 detection in exhaust gases at 400-550°C. Electrical polarization applied between working and counter electrodes accelerates partial electrochemical reaction: oxygen reduction on cathode and oxygen-ion oxidation on anode. Variation of working electrode potential, where NO2 reduction is possible, is proportional to NO2 concentration. Cross-sensitivity of sensor to hydrocarbons, NO and CO was not observed. Combination with a catalytic filter allows NO measurement and distinction between NO and NO2, given that oxygen concentration is known and ammonia concentration remains negligible.Motivation The interest for reliable electrochemical gas sensors for automotive exhausts application to on-board control the emissions of nitrogen oxides is still challenging with the strengthening of international legislations. Electrochemical NOx sensors based on yttria-stabilized zirconia (YSZ) solid electrolyte have been and are still extensively studied, focusing either on materials approach or on running mode (polarization). In a past project, a planar potentiometric YSZ based sensor with platinum and gold electrodes associated with a catalytic filter covering the sensing element was shown to be fully selective to NOx but unable to distinguish between NO and NO2. Without a catalytic filter, the Au/YSZ/Pt sensor is sensitive to reducing gas (CO, hydrocarbons, NO…) with a positive response (&#916V= VPt-VAu) while opposite behavior is observed for oxidant gas NO2. A catalytic filter removes interferences from CO and hydrocarbons and leads to NO/NO2 thermodynamic equilibrium so that a similar response is obtained either for NO or NO2. Hence, the objective is to improve such sensor to overcome this inconvenient; a strategy based on electrode polarization was developed

Identification of point defects in tin dioxide: Experimental and theoretical approach

International audienceThermoluminescence (TL) glow curves of polycrystalline tin dioxide samples exhibit three main peaks below room temperature. Their relative intensities depend on experimental conditions. Especially, they are modified by aluminum doping or by wet air exposition. In SnO2, we suggest that ionised oxygen vacancies and hydroxyl groups are responsible for thermoluminescence. This assumption is discussed. In order to explain the behaviour of these defects, two kinds of modelling are proposed

Tin dioxide thin-film gas sensor prepared by chemical vapour deposition : Influence of grain size and thickness on the electrical properties

International audienceTin dioxide films are elaborated by a chemical vapour deposition (CVD) method. An accurate control of deposition parameters (temperature, total pressure, duration) so that appropriate annealing conditions (duration, temperature) can be used to modify the structural properties of the films: grain size, thickness, and stoichiometry. Important modifications of electrical performances in tin dioxide films for gas-sensing applications are observed. A correlation between structural properties of CVD films and their electrical behaviour is proposed. The main results are: (i) a sharp increase in the electrical conductance under pure air G0 from a critical value of the grain size D=2L, due to the apparition of a conduction channel between adjacent grains; the depletion layer L is evaluated to 35 Å; (ii) a dependence of the electrical conductance G0 with stoichiometry observed for various deposition temperatures and various annealing conditions; the predominant effect of stoichiometry variations for films deposited at high temperature (100-300 Å grain size range) is responsible for the decrease of G0, and (iii) a strong influence of film thickness e, with a maximum of sensitivity for the thinnest films, in which tin dioxide is more discontinuous and disordered, and an increase in G0 with e due to the increase of the number of percolation paths up to 3000 Å corresponding to a percolation threshold

Functionalization of APTES modified tin dioxide gas sensor

Communication présentée dans la session "Metal Oxide Gas Sensor".International audienceSummary In the present work, commercial SnO2 powder was used for sensor thick film fabrication. The film was produced using screen printing technology. The SnO2 functionalization was done with 3-aminopropyltriethoxysilane (APTES) in liquid phase as an intermediate step, followed by functionalization using hexanoyl chloride exhibiting an alkyl end functional (CH3) group. The SnO2 sensor modified with alkyl end group was found to be sensitive to ammonia gas at 100°C. The advantages are the reduction of the power consumption by decreasing the operating temperature, and the enhancement of the selectivity and sensitivity to the gas with respect to pure SnO2 sensor.MotivationMolecularly modified metal oxide gas sensors have shown to be promising devices for selective gas sensor related to disease diagnosis. Those sensors can be used to detect the gas emanated from the human body for breath analysis application. Tin dioxide sensors have lack of selectivity and work at high temperature (350-500°C). The need of selective sensors with high sensitivity at low gases concentration pushes us to modify SnO2 sensing element in order to change its interactions with gas. The modification with organic functional groups with different polarities change the sensor response to specific gases depending on their polarity. A SnO2 functionalization based on APTES combined with hexanoyl chloride was investigated. Another objective is to reduce the power consumption by decreasing the operating temperature