146 research outputs found

    CO detection in H2 reducing atmosphere with mini fuel cell

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    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

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    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

    Développement d'une pile à combustible à oxyde solide de type monochambre fonctionnant sous mélange air/méthane

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    Cette étude est consacrée au développement d une pile à combustible à oxyde solide (SOFC) de type monochambre. Contrairement à une pile SOFC conventionnelle, le système monochambre fonctionne dans un mélange de gaz hydrocarbure/air ce qui permet de s affranchir des contraintes d étanchéités. Le principe de fonctionnement est basé sur la différence d activité catalytique entre l anode et la cathode : l anode doit être sélective à l oxydation des hydrocarbures et la cathode à la réduction de l oxygène. La configuration monochambre implique cependant de nouvelles contraintes concernant notamment la stabilité des matériaux sous mélange hydrocarbure/air à haute température.L objectif de cette thèse est d optimiser les performances d une pile monochambre fonctionnant sous mélange méthane/oxygène et d améliorer la compréhension de ce système.Les différents éléments d une pile (électrolyte, cathode, anode) ont été caractérisés sous mélange méthane/oxygène. Quatre matériaux de cathodes (LSM, BSCF, SSC, LSCF) ont été comparés au niveau de leur activité catalytique, stabilité, conductivité électrique et résistance de polarisation. Une étude catalytique de l anode a été réalisée afin d identifier les réactions chimiques qui se produisent. Une étude de pile complète en géométrie électrolyte support a permis de sélectionner le matériau de cathode LSCF. Cette étude a également mis en évidence la nécessité de diminuer l épaisseur de l électrolyte, la géométrie anode support a donc été étudiée. La première pile anode support a présentée une anode inhomogène et un électrolyte poreux. Des travaux ont été menés afin d homogénéiser l anode et de diminuer la porosité de l électrolyte. En optimisant les conditions de fonctionnement (température et rapport CH4/O2), une densité de puissance maximale de 160 mW.cm-2 a été obtenue.This study is devoted to the development of a single-chamber solid oxide fuel cell. Contrary to a conventional solid oxide fuel cell, a single chamber fuel cell works under a hydrocarbon/air mixture with no more sealing needed. The working principle of this device is based on the difference of catalytic activity between the anode and the cathode: the anode must be selective to hydrocarbon oxidation and the cathode to oxygen reduction. With single-chamber geometry, chemical stability of materials has to be taken into account under hydrocarbon/air mixture at high temperature.The goal of this work is to optimize the performances of a single-chamber cell working under methane/oxygen mixture and to improve this device comprehension.Each part of the cell (electrolyte, anode, cathode) was characterized under methane/oxygen mixture. Four cathode materials (LSM, BSCF, SSC, LSCF) were compared regarding their catalytic activity, stability, electrical conductivity and polarization resistance. The catalytic activity of the anode was studied in order to identify the chemical reactions happening. A study of electrolyte supported cells showed that LSCF material is the most suitable cathode. Furthermore, this study showed that the electrolyte was too thick; the anode supported configuration was studied. The first anode supported cell showed an inhomogeneous anode and a porous electrolyte. From that, a study of the homogeneity of the anode and the densification of the electrolyte was performed. A maximum power density of 160mW.cm-2 was obtained by optimizing the working conditions of the cells (temperature and CH4/O2 ratio).ST ETIENNE-ENS des Mines (422182304) / SudocSudocFranceF

    Laser induced densification of cerium gadolinium oxide: application to single-chamber solid oxide fuel cells

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    International audienceIn single-chamber solid oxide fuel cells (SC-SOFC), anode and cathode are placed in a gas chamber where they are exposed to a fuel/air mixture. Similarly to conventional dual-chamber SOFC, the anode and the cathode are separated by an electrolyte. However, as in the SC-SOFC configuration the electrolyte does not play tightness role between compartments, this one can be a porous layer. Nevertheless, it is necessary to have a diffusion barrier to prevent the transportation of hydrogen produced locally at the anode to the cathode that reduces fuel cell performances. This study aims to obtain directly a diffusion barrier through the surface densification of the electrolyte Ce0.9Gd0.1O1.95 (CGO) by a laser treatment. KrF excimer laser and Yb fiber laser irradiations were used at different fluences and number of pulses to modify the density of the electrolyte coating. Microstructural characterizations confirmed the modifications on the surface of the electrolyte for appropriate experimental conditions showing either grain growth or densified but cracked surfaces. Gas permeation and electrical conductivities of the modified electrolyte were evaluated. Finally SC-SOFC performances were improved for the cells presenting grain growth at the electrolyte surface

    Développement d'une cellule SOFC de type monochambre pour la conversion en électricité des gaz d'échappement d'un moteur thermique

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    Le projet présenté dans ce mémoire a pour objectif de développer un système de récupération d énergie des gaz d échappement d un véhicule à essence. Constitué de piles à combustible à oxyde solide (SOFC) en configuration monochambre, le dispositif doit convertir l énergie chimique des gaz imbrûlés en électricité. Son fonctionnement en aval du catalyseur trois voies permettrait de compléter son action dépolluante tout en améliorant l efficacité énergétique du véhicule. Par opposition aux piles SOFC dites conventionnelles, les piles SOFC monochambres ne nécessitent pas de scellement étanche entre les compartiments et fonctionnent sous un mélange gazeux composé d hydrocarbures et d oxygène. L empilement en stack de plusieurs cellules est simplifié et plus compact, son intégration au cœur du pot d échappement est donc plus simple. Ce concept a été précédemment étudié dans la littérature et le présent projet a pour but d améliorer les performances délivrées en optimisant certains paramètres : la géométrie de pile et les matériaux d électrodes et d électrolyte. De plus, un mélange gazeux plus représentatif des conditions réelles a été défini et utilisé tout au long du projet. Une étude préliminaire sur les matériaux sous forme de poudre a permis de réaliser un premier choix parmi quatre matériaux de cathode et de définir les conditions de fonctionnement théoriques des cellules. Ensuite, les cellules complètes ont été mises en forme puis étudiées sous mélange gazeux. Une densité maximale de puissance de 25 mW.cm-2 à 550C pour une cellule Ni-CGO/CGO/LSCF-CGO a ainsi pu être obtenue.This study aims at developing a system able to recover energy from exhaust gases of a thermal engine. Composed of Solid Oxide Fuel Cells (SOFC) in a single chamber configuration, the device has to convert chemical energy of gases into electricity. Embedded in the exhaust line at the exit of the three-way catalyst, the stack of single chamber SOFC will complete the reduction of toxic gases emissions with an improvement of the vehicle energy efficiency.Unlike conventional SOFC, single chamber SOFC do not require any gastight sealing between compartments and work in a mixed atmosphere composed of hydrocarbon and oxygen. Stack assembly is thus simplified and more compact; insertion into the exhaust line is therefore easier. This concept has been previously studied in the literature and this work aims at enhancing performances through the optimisation of some parameters such as cell geometry and cell components materials.Moreover, a more representative gas mixture of actual compositions in the exhaust line has been defined and used all along this project. A preliminary study on the raw materials has allowed to make a first selection among four cathode materials and to define theoretical working conditions of our cells. Afterwards, cells have been elaborated and then studied in the selected gas mixture. A maximum power density of 25 mW.cm-2 has been obtained at 550C for a Ni-CGO/CGO/LSCF-CGO cell.ST ETIENNE-ENS des Mines (422182304) / SudocSudocFranceF

    Modeling of the signal of a resistive soot sensor, influence of the soot nature and of the polarization voltage

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    International audienceResistive soot sensors capable of measuring the mass concentration of particles in an exhaust pipe have been developed in a previous work. In particular, it has been shown that these sensors have an optimal sensitivity for a certain polarization voltage depending on the nature of the particles.This work shows that this effect can be explained by an equilibrium between the creation of soot bridges between the two collecting electrodes and their destruction initiated by Joule effect due to the polarization voltage. Based on this assumption, a model is proposed to predict the load curve (response versus time) of the sensor. In addition, the high frequency sampling of the sensor response has revealed some jumps of the sensor response (electrical conductance), which are exploited through a statistical approach to obtain additional information on the nature of the collected particles

    A novel approach of a fully inkjet printed SnO<sub>2</sub>-based gas sensor on a flexible foil

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    International audienceIn recent years, printed and flexible gas sensors have quickly emerged as an innovative area of great interest because of their lightness and low cost. These flexible sensors can be easily integrated into autonomous systems for many applications such as smart food packaging and premature disease detection. In this paper, a novel approach was applied to manufacture a fully inkjet-printed gas sensor on a flexible polymeric foil. Platinum heater and gold electrodes were printed on the top side of the substrate, separated by a thin insulating layer of printed polyimide. An aqueous sol-gel process was adopted to synthesize nanosized SnO2-based sol that guaranty a crystallization at 350 °C, which is entirely consistent with the polyimide foil. Then, the sol was transformed into a stable ink and inkjet printed over the gold electrodes. The printability of different inks was optimized to ensure flawless ejection of droplets, and the complex physico-chemical interactions between the inks and different interfaces were controlled to get well-defined patterns with high resolution. Finally, electrical measurements of the printed sensor were performed to characterize the response and the sensitivity to different concentrations of ethanol, ammonia and carbon monoxide gases, at working temperature of 300 °C, in dry and wet air

    Development of a sensitive and selective mixed-potential ammonia sensor for automotive exhausts

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    Session: A5 Oxide Based Sensors and ActuatorsInternational audienceOne of the most effective technologies in decreasing large-scale NOx emission produced by diesel engine vehicles is Urea-SCR (selective catalytic reduction) system. In order to prevent inducing excessive ammonia to the environment, an NH3 sensor is required at the exit of this system. In this study, highly selective ammonia sensors were developed to detect ammonia emissions from automotive exhaust.The sensors were fabricated with 8-YSZ electrolyte, a platinum reference electrode and a working electrode of Au-V2O5 (mass ratio: 85:15), screen-printed on an alumina supports. A platinum resistor was printed at the backside of the support to control the sensor temperature. The measured sensor response (ΔV) is the potential difference between reference and working electrodes. Figure 1 shows the responses of two identical sensors to 100 ppm CO, NO2, NO and 20 ppm of NH3 at four different temperatures. It can be seen that the sensors respond to all gases at lower temperatures while by increasing temperature to 600 °C the selectivity to NH3 is greatly improved. The selectivity of sensors was also confirmed by testing other possible interfering gases and no responses were observed for 20ppm of H2 and 100ppm of a hydrocarbon mixture. The stability of such sensors was studied at 550 °C and 600 °C. Since sensors showed no long term stability at 600 °C (electrode degradation), but remain stable results at 550 °C, investigations were made to decrease the selective working temperature while maintaining selectivity. After testing different mass percentages of V2O5 in working electrode, we observed that by increasing this value to 50%, the working temperature of selective ammonia sensors could be decreased to 550 °C with stable responses. Further investigations will be performed in order to gain deeper insight in sensing mechanism of V2O5 based working electrodes, which governs the sensor’s performance

    Influence of key parameters on the response of a resistive soot sensor

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    International audienceThis paper is a comprehensive study dealing with the parameters that influence the response of a resistive soot sensor which was developed for Diesel Particulate Filter (DPF) failure detection in a past project. From the conductance measurement between two Pt electrodes, and a regeneration strategy, this kind of sensor can provide the weight concentration of particulate matter (PM). In this study, we have characterized and determined the key parameters such as the PM distribution size and the polarization voltage between the electrodes that could influence the sensor response. First results show that the sensor response strongly depends on the polarization voltage applied between the two electrodes

    Anode supported single chamber solid oxide fuel cells operating in exhaust gases of thermal engine

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    International audienceThis project deals with the development and the electrochemical characterization of anode supported single chamber SOFC in a simulated environment of thermal engine exhaust gas. In the present work, a gas mixture representative of exhaust conditions is selected. It is composed of hydrocarbons (HC: propane and propene), oxygen, carbon monoxide, carbon dioxide, hydrogen and water. Only oxygen content is varied leading to different gas mixtures characterized by three ratios R = HC/O2. Concerning the cell components, a cermet made of nickel and an electrolyte material, Ce0.9Gd0.1O1.95 (CGO) is used as anode and two cathode materials, La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) and Pr2NiO4+δ (PNO), are evaluated. The prepared cells are investigated in the various gas mixtures for temperatures ranging from 450 °C to 600 °C. Ni-CGO/CGO/LSCF-CGO cell has delivered a maximum power density of 15 mW cm−2 at 500 °C with R = HC/O2 = 0.21, while lower power densities are obtained for the other ratios, R = 0.44 and R = 0.67. Afterwards, LSCF and PNO cathode materials are compared and LSCF is found to deliver the highest power densities. Finally, by improving the electrolyte microstructure, some cells presenting a maximum power density of 25 mW cm−2 at 550 °C are produced. Moreover, up to 17% of initial HC are eliminated in the gas mixture
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