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International audience; Comprehension of oxidation processes under the influence of an external polarization is still a challenge, despite numerous past studies. In this study, thermogravimetric analysis technique coupled with in situ application of an electric voltage was used to investigate oxidation of zirconium. The first technical challenge was to modify the thermobalance to integrate it with polarization equipment without perturbation of measurement and of oxidation behavior. Surprisingly, the oxidation rate was found to remain independent on the applied voltage, despite a large range of applied potentials, ± 200 V. Modeling of oxidation rates according to diffusion mechanism combined with investigation of polarization curves of the metal/oxide/electrode system has shown that a high electrical resistance appears at the oxide/electrode interface, even with addition of an intermediate gold layer. This resistance prevents from generating sufficient voltage drop through the oxide layer (> 10 V), necessary to modify the kinetics. Nevertheless, meaningful electrochemical properties using analogy with solid-oxide fuel cells have been observed, allowing to propose a comprehensive approach of oxidation phenomena under polarization.

International audience; During a fire in an industrial facility, the main consequences concerning aerosol are the production of large amount of soot and potential resuspension of hazardous material in particulate form. Soot deposition quantification on walls in a room during a fire is essential for the prediction of aerosol quantities that can be transported in the ventilation ducts and clog high efficiency particulate air filters.For this purpose, accumulative resistive sensors, initially developed for monitoring Diesel Particulate Filters (DPF), have been used to quantify soot particles that are deposited on its sensing side. After validation of the fabrication process via electrical measurements, the sensor response has been studied under different polarization voltages and an experimental protocol for soot quantification has been qualified.Thanks to those protocols, it was first demonstrated that the polarization voltage has no influence on the deposition velocity. Then, the resistive sensor was calibrated at polarization voltages of 10 V and 0.1 V. For 0.1 V, results are less repeatable and do not allow to propose a correlation between conductance and deposited mass. Better repeatability was found for a polarization voltage of 10 V allowing to propose and develop a calibration procedure aiming to correlate sensor conductance and deposited mass of aerosol. Indeed, it was proved that the sensor has a blind zone, in terms of conductance, for mass deposit ranging from 0 to 230 mg/m2. A linear calibration curve with a good sensitivity of 2.49 µS.mg-1.m2 was obtained for deposited mass between 230 and 1630 mg/m2.

International audience; In the present study, Au-V2O5 sensing material was tested as a sensing electrode for developing mixed-potential ammonia gas sensors. The results of gas sensing measurements indicated selective responses to NH3 while this selectivity was highly dependent on the temperature. Different V2O5 contents were tested in the sensing electrode. The results showed that by increasing V2O5 content from 15 wt.% to 50 wt.%, selective ammonia sensors could be achieved at 550 °C. The selectivity of Au-50%V2O5 sensor was also confirmed in gas mixtures of CO, NH3, NO, and NO2 gases. Modeling of the sensor responses in the ammonia concentration range 2-40 ppm at four oxygen concentrations was performed based on mixed-potential theory. Nernst and Butler-Volmer equations with an electron transfer assumption were used for data modeling.

International audience; In 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.

International audience; In this contribution brownmillerite-based nanocomposite cathode for Single-Chamber Solid Oxide Fuel Cells is developed. These cells can be very attractive especially for small and cheap devices because of the absence of seals. The efficiency of SC-SOFCs is strictly connected to the selectivity of anode and cathode, the bottleneck for this technology. The development of a cathode inert in fuel oxidation is particularly challenging. Our strategy is to start from a catalytically un-active support (CFA = Ca2FeAl0.95Mg0.05O5) and induce the formation of iron oxide based nanoparticles, expected to activate oxygen. Symmetric (CFA + FeOx/CGO/CFA + FeOx) and complete cells (CFA + FeOx/CGO/Ni-CGO) are studied in air and methane/oxygen 2:1 mixture. The Area Specific Resistance of CFA + FeOx is less than 1/3 that of CFA. The high selectivity allows to reach an efficiency of 25%; power still needs to be increased but we demonstrated the possibility to develop selective low cost electrodes. The effect of air, methane/oxygen exposure and the heat treatments were carefully investigated.

Ce congrès est un événement digital: 4th international nanoFIS 2020 conference – 100% Digital at highest scientific level!; International audience; Ammonia detection at ambient with low-cost sensors is a challenge for various applications like breath analysis and agriculture. Such a challenge can be reached with functionalized SnO2 based gas sensors using silanization by 3-aminopropyltriethoxysilane (APTES) as an intermediate step before grafting with functional end group providing selectivity for the target gas. Moreover, operation at room temperature gives the opportunity to develop a sensor on a plastic substrate entirely manufactured by inkjet technology, by developing suitable inks, in particular to obtain SnO2 sensing element.

This study reports the catalytic properties of Ag nanoparticles dispersed on mixed ionic and electronic conducting layers of LSCF (La0.6Sr0.4Co0.2Fe0.8O3) for propene combustion. A commercial and a synthesized LSCF powder were deposited by screen-printing or spin-coating on dense yttria-stabilized zirconia (YSZ) substrates, an oxygen ion conductor. Equal loadings (50 &micro, g) of Ag nanoparticles were dispersed via drop-casting on the LSCF layers. Electrochemical and catalytic properties have been investigated up to 300 &deg, C with and without Ag in a propene/oxygen feed. The Ag nanoparticles do not influence the electrochemical reduction of oxygen, suggesting that the rate-determining step is the charge transfer at the triple phase boundaries YSZ/LSCF/gas. The anodic electrochemical performances correlate well with the catalytic activity for propene oxidation. This suggests that the diffusion of promoting oxygen ions from YSZ via LSCF grains can take place toward Ag nanoparticles and promote their catalytic activity. The best specific catalytic activity, achieved for a LSCF catalytic layer prepared by screen-printing from the commercial powder, is 800 times higher than that of a pure Ag screen-printed film.

One 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 [1, 2]. 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 substrate. 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: no responses were observed for 20ppm of hydrogen and 100ppm of a hydrocarbon mixture. The stability of such sensors was studied at 550°C and 600°C. Since the sensors show no long-term stability at 600°C (electrode degradation), but remain stable at 550 °C, investigations were made to decrease the 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. References [1] K. Shimizu, I. Chinzei, et al. "Doped-vanadium oxides as sensing materials for high temperature operative selective ammonia gas sensors," Sensors and Actuators B, 141, 2009, pp. 410-416. [2] M. Van Nieuwstadt, I. Dpadhyay, et al. "Control of Urea SCR Systems for US Diesel Applications" in IFP Energies Nouvelles International Conference, Dearborn, USA, 2011, pp. 655-665. Figure 1

International audience; Laser induced densification of ceramic oxide has shown great promises. However to control this process in regards of the final properties of the material, it is necessary to understand phenomena occurring during laser matter interaction, especially heat diffusion through the material. A thermal simulation of cerium gadolinium oxide (CGO) submitted to infrared laser pulses is presented. In order to determine the temperature profile during laser treatment, optical properties of CGO must be known; for this purpose, ellipsometry measurements were performed in order to obtain absorption coefficient and reflectivity. Finally, a thermal model based on heat equation was developed. Experimental observations of irradiated CGO surfaces were in agreement with the simulation results, in particular at maximum temperature when the material reaches fusion.

Catalytic and electrocatalytic tests have been carried out in a solid oxide cell for propylene combustion using two different Ag screen-printed films deposited on yttria-stabilized zirconia. Competitive adsorption between oxygen and propylene has been observed at 300 °C. Catalytic performances can be tailored by current application in a non-Faradaic manner. The predominant impact of current applications is to modify the reactivity of oxygen present on the Ag surface. Positive current applications enhance the propylene conversion by producing more reactive oxygen species. This beneficial effect is more pronounced under lean-burn conditions where the oxygen coverage on Ag is high.

International audience; Ethylene oxide (EO) is industrially produced by epoxidation of ethylene on Ag-based heterogeneous catalysts. Electrophilic oxygen species are assumed to be active key species in the EO production. This study explores the possibility to electrochemically produced these oxygen species in a solid oxide electrochemical cell. Two series of Ag based cermet electrodes were prepared either with Yttria Stabilized Zirconia (YSZ), a pure oxygen ionic conductor, or with Gadolinia-Doped Ceria (GDC), a mixed ionic and electronic conductor. Ag/YSZ cermet layers were deposited on planar and tubular YSZ dense substrates by using a conventional chemical method while Ag/GDC cermets were coated on GDC dense pellets by reactive magnetron sputtering. We evidenced a self-redispersion of Ag in the ethylene/oxygen mixture in Ag/YSZ cermet layers leading to the formation of small Ag clusters in close interaction with YSZ which are selective for epoxidation. However, the sintering process of these small Ag clusters is too fast even at 260°C to maintain the EO selectivity. On the other hand, the selectivity towards EO and the ethylene conversion of Ag/GDC cermet coatings were found to linearly increase with the applied current, demonstrating for the first time, the direct electrooxidation of ethylene into EO.

International audience; The European standards “Euro” limit the emission of several pollutants from thermal engine vehicles. The particle number (PN) and particulate mass (PM) emissions are specifically limited since 2011, hence modern Diesel engines are equipped with a Diesel particulate filter (DPF). On-board diagnostic (OBD) regulations impose to perform the self-diagnostic of the DPF. Nowadays, this diagnostic is done through a very simple backpressure monitoring, but the forthcoming steps will probably require a more sophisticated system, such as a resistive soot sensor. The aim of this study is to investigate the mechanisms leading to the formation of bridge-like soot deposits brought to light by scanning electron microscopy. A 2D model taking into account the aerodynamic transport and the electrostatic effects was used to improve our understanding of the soot deposition process. The model presented in this paper includes a force that has been neglected so far in previous works about resistive soot sensors: the dielectrophoresis. In this theoretical frame, this force affects particles motion in such a way that they tend to numerically build the bridge-like structures that are observed experimentally. Simulation shown that the dielectrophoresis mainly impact large particles – over 150 nm diameter.

International audience; Resistive 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.

In this study, we have investigated, for the very first time, the oxygen electrode reactions on Ag/YSZ electrochemical catalysts both in oxygen and under reaction conditions compatible with the ethylene epoxidation reaction. Electrochemical Impedance Spectroscopy (EIS) in combination with in-situ Raman spectroscopy and catalytic activity measurements were used to identify and understand the main oxygen reaction pathways. The results obtained suggested that the rate limiting step under an O2 reaction atmosphere (at 300 °C) is the O2 adsorption/dissociation process on the Ag catalyst-electrode. In addition, the polarization resistance increased with time under the presence of O2. This was attributed to the formation of Ag2O on the catalyst surface or near surface, which limits the oxygen electrode reactions. Finally, we observed that the addition of ethylene in the feed stream hinders the electrode reaction, due to its competitive chemisorption with oxygen on Ag. These results give new insights into the design of selective Ag/YSZ catalyst for ethylene epoxidation. Keywords: Electrochemical Impedance Spectroscopy (EIS), Oxygen electrode reaction, Ag/YSZ, Ethylene epoxidation

Editorial; International audience; EUROSENSORS 2017, the XXXI edition of the conference series, was held in PARIS at UIC-P Congress Center close to the Tour Eiffel, from September 3 to 6, 2017 for the third time in France, after Toulouse 1994 and Lyon 2007. Since 1987 the EUROSENSORS Conference is a unique forum for scientists and engineers from academia, research institutes and industry to present their latest results in the field of Sensors, Actuators, Microsystems and Nanosystems. EUROSENSORS 2017 was attended by 500 participants, 85% of them came from academia and 15% from industry and research facilities. 472 submissions were received from 39 countries for peer review, all being assigned to 4 reviewers. From the accepted ones, 146 lectures (including 4 plenary talks) were selected and presented in 12 topics, with focus on “Printed and flexible electronics” and “Sensors for Factory of the future”. 247 posters were presented and displayed during the entire duration of the conference.On Sunday 3 September, EUROSENSORS SCHOOL focused on “Printed and flexible electronics” was attended by 45 persons.

ISSN: 2504-3900; International audience; The development of selective and cheap metal oxide gas sensor at ambient temperature is still a challenging idea. In this study, SnO2 surface functionalization was performed in order to obtain sensitive and selective gas sensor operated at ambient temperature. 3-aminopropyltriethoxysilane (APTES) was used as an intermediate step, followed by functionalization with molecules having acyl chloride with different end functional groups molecules such as alkyl, acid and ester groups. Acid and ester modified sensors are sensitive to ammonia between 0.2 and 10 ppm at room temperature. However, ester modified SnO2 is more selective than acid modified sensor regarding ethanol and carbon monoxide gases.

ISSN: 2504-3900; International audience; Among all NOx reduction approaches, selective catalyst reduction (SCR) system is one the most reliable ways to control NOx emissions from diesel engine vehicles and trucks. In order to optimize the conversion rates of NOx and to prevent inducing excessive NH3 to the air, an NH3 and NOx sensor is required [1]. In this study, three different types of YSZ ink have been examined to identify the most effective electrolyte for NOx and NH3sensing. The results have shown that a home-made ink with YSZ powder shows the best sensitivity towards ammonia without polarization and the highest NO2/NO signal ratio with polarization current of 25 nA.

ISSN: 2504-3900; International audience; Sol based SnO2 precursor was synthetized by aqueous sol-gel route, then transformed into a stable ink with appropriate viscosity and surface tension to be inkjet printed and sintered at relatively moderate temperature. Plastic foil with thickness of 50 µm was selected as substrate for its high thermal resistance and stability (Upilex-50S). Prepared sol and formulated ink were both characterized by analytical techniques; electrical measurements were performed on the printed sensing film to characterize the response to CO gas in different concentrations, at working temperature of 300°C.

International audience; In 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.

International audience; Electrochemical NOx sensors based on yttria-stabilized zirconia (YSZ) are commercialized to detect overall NOx concentrations in Diesel exhausts without distinction between NO and NO2. To overcome this inconvenient, a high-sensitive sensor based on selective electrochemical reduction of NO2 is proposed. An electrochemical cell consisting of three metallic electrodes on solid-state electrolyte (YSZ) operating under electric polarization between a gold working electrode and a platinum counter electrode allows selective NO2 detection at 400-550°C with high sensitivity, and without any significant interferences to other gases like hydrocarbons, carbon monoxide and also ammonia and nitrogen monoxide. A mechanism based on cathodic overpotential is proposed.

Catalytic and electrocatalytic measurements have been carried out in a solid oxide cell for propylene combustion using continuous Ag catalytic films and Ag nanoparticles dispersed on a mixed ionic electronic conductor film deposited on yttria-stabilized zirconia. Similar EPOC behaviors were observed for both samples, indicating that dispersed Ag nanoparticles in LSCF can be electropromoted in a reversible and non-Faradaic manner under lean-burn conditions. Key words: Electrochemical Promotion of Catalysis (EPOC); Propylene Combustion; Ag Catalytic films; dispersed Ag nanoparticles. Introduction: Catalytic combustion as a process used for removal of hydrocarbons from automotive gas exhausts or for energy production has been widely implemented on supported PGM (Platinum Group Metals) based catalysts. Since PGMs are very costly and rare, there is a strong need for an equally effective and less expensive catalyst. The electrochemical promotion of catalysis (EPOC), is a promising concept to in-operando boost catalytic processes in a reversible and controlled manner. The aim of this study was to develop Ag-based electrochemical catalysts for low temperature propylene deep oxidation. The magnitude of the electrochemical promotion has been investigated on continuous screen-printed Ag films as well as on Ag nanoparticles dispersed into the porosity of LSFC (La0.8Sr0.2Co0.2Fe0.8O3), a mixed ionic electronic conductor (MIEC). Experimental: Nanostructured electrochemical catalysts were prepared by screen-printing and by wet impregnation method. Catalytic and electrocatalytic tests have been carried out in a specific quartz reactor1 which operated under continuous flowing conditions at atmospheric pressure. The catalytic activity was monitored in a temperature range of 100 to 400 oC under lean-burn conditions, as encountered in Diesel exhausts. The most active Ag films were also evaluated under closed circuit conditions in order to measure the impact of polarization between the silver working electrode and a Au reference electrode. Both electrodes were exposed to the same atmosphere in a single chamber configuration. Results and discussion: Figure 1 shows typical catalytic activity measurements under current application for a Ag/YSZ sample (a) and a Ag/LSCF/YSZ sample (b) under lean-burn conditions, at 300 oC. The OCV propylene conversion is twice on the dispersed Ag nanoparticles despite a two orders of magnitude lower Ag loading. Furthermore, similar EPOC behaviors were observed for both samples, indicating that dispersed Ag nanoparticles in LSCF can be electropromoted in a reversible and non-Faradaic manner. The predominant impact of current applications is to modify the reactivity of oxygen present on the Ag surface. Conclusions: This study reports, for the first time, that the catalytic activity for propylene combustion of Ag coatings and Ag nanoparticles supported on LSCF both deposited onto YSZ can be tailored by current applications in a non-Faradaic manner. This study also demonstrates that EPOC can enhance catalytic properties of Ag nanoparticles dispersed in a MIEC layer for the abatement of propylene in air. Acknowledgments: This study was performed in the “EPOX” project, funded by the French National Research Agency (ANR), ANR-2015-CE07-0026. References [1] I. Kalaitzidou, T. Cavoue, A. Boreave, L. Burel, F. Gaillard, L. Retailleau-Mevel, E.A. Baranova, M. Rieu, J.P. Viricelle, D. Horwat, P. Vernoux, Cat. Com., 104 (2018) 28-31. Figure 1

International audience; Mixed potential ammonia gas sensors were fabricated by using two sensing materials of Ni3V2O8 and Au-V2O5 as working electrodes, YSZ as electrolyte and platinum as reference electrode. The results have shown that the Ni3V2O8 sensors show cross-sensitivity toward NO gas. However, Au-V2O5 working electrodes displayed a high sensitivity to NH3 as well as very fast response and recovery times at high temperatures. Furthermore, the results indicate that the selectivity of Au-V2O5sensors increases by increasing temperature.

International audience; In this work, a flexible tin oxide (SnO2) gas sensor was successfully fabricated by inkjet printing technology. This thin film deposition technique requires the formulation of stable suspensions with specific fluidic properties. Aqueous Sol-gel method was applied to synthesize astable sol based on tin oxide, then transformed into ink with the appropriate viscosity and surface tension to be printed using a drop-on-demand piezoelectric inkjet printer. Thermal analyses of synthetized sol show that a crystallized structure of SnO2 could be obtained at 350 °C, which is lower than crystallization temperatures of SnO2 previously reported in the literature, and entirely consistent with our plastic substrate. The printed thin-film was then sintered at 350 °C on polyimide foil (Upilex-50S) and characterized as sensor.

International audience; Since 2011, Euro 5b European standard limits the particle number (PN) emissions in addition to the particulate matter (PM) emissions. New thermal engines equipped vehicles have to auto-diagnose their own Diesel particulate filter (DPF) using on-board diagnostic (OBD) sensors. Accumulative resistive soot sensors seem to be good candidates for PM measurements. The aim of this study is to bring more comprehension about soot micro-structures construction in order to link the response of such a sensor to particle size and PN concentration. The sensor sensitivity to the particlesize has been studied using successively an electrostatic and an aerodynamic classification, showing the same trend.

International audience; The fabrication of printed electronic devices based on metal oxide inks requires the formulation of stable suspensions with specific fluidic properties. In our work, a tin oxide based solution was synthesized by aqueous sol–gel method and transformed into an ink with appropriate viscosity and surface tension to be inkjet-printed on polyimide foil and sintered at relatively low temperature. Thermal analysis by TGA/DSC and microstructural analysis by XRD of synthesized sol show that a crystallized structure of SnO2 could be obtained at 350 °C, which is lower than crystallization temperatures of SnO2 previously reported in the literature, and entirely consistent with the use of polyimide foil. The stability and the rheological properties of the ink were studied to ensure the jettability criteria of the inkjet printer. Electrical measurements of the printed sensing films were performed to characterize the response to CO gas in different concentrations, at working temperature of 300 °C.

International audience; In this work, La2NiO4+δ is used as cathode material for Intermediate temperature solid oxide fuel cells (IT-SOFC). Scanning electron microscopy, X-ray diffraction, and electrochemical impedance spectroscopy are used to investigate the effect of the presence of an ultrathin La2NiO4+δ layer (80 nm) deposited by dip-coating or sputtering at the interface YSZ/La2NiO4+δ. The thick porous cathode layer of La2NiO4+δ is deposited by screen-printing, and sintered at 1000 °C for 2 h or 1200 °C for 20 min in order to study the effect of sintering temperature on the electrochemical properties. The results show that the electrochemical performances of the cathode are influenced by the deposition technique. The best electrochemical properties are obtained with the use of the nano film interface layer deposited by sputtering. The introduction of ultrathin interface with nano grained between the cathode and electrolyte is a promising technique to reduce polarization resistance associated with oxygen reduction reaction (ORR) on the cathode.

International audience; In order to deal with the well-known lack of selectivity of SnO2 based gas sensors, the functionalization of SnO2 was performed. Liquid silanization by 3-aminopropyltriethoxysilane (APTES) was used as an intermediate step, followed by functionalization with molecules bearing acyl chloride with alkyl or ester end functional groups. Modified sensors with APTES, alkyl and ester end functional groups were successfully characterized by Attenuated Total Reflectance-Fourier Transform Infrared spectroscopy (ATR-FTIR). No response was observed for APTES and alkyl modified SnO2 sensors to ammonia gas at room temperature while the SnO2 sensor modified with ester end group was found to be sensitive and selective to ammonia gas at room temperature. This implies that the response is generated by ester functional groups. Working at low temperature is also one of the advantages of these sensors as well as the selectivity with respect to other gases like acetone and ethanol.

International audience; Solid Oxide Fuel Cells (SOFCs) are electrochemical devices capable of converting and storing energy in a sustainable and efficient way. The decrease of the operating temperature could be of great help for their diffusion. The use of nanocomposites is a smooth way to design materials with many advanced functionalities that could not be reached at the same time with only a single component. Two LSGF (La0.6Sr0.4Ga0.3Fe0.7O3) nanocomposites have been synthesized by wet impregnating manganese and iron oxides (MOx+LSGF, with M = Fe/Mn). The composites’ powders have been extensively characterized by means of XRD, XPS, N2-asdorption, SEM, EDX, TPR, O2-TPD and the results compared with those obtained for LSGF. The supporting perovskite stabilizes the lower oxidation states of Mn and Fe and a deep interaction between the deposited oxides and the perovskite surface is evident. Both Mn and Fe diffuse inside the perovskite during thermal treatments and this phenomenum greatly affect oxygen vacancies, mobility, and exchange capability. The catalytic activity for methane oxidation is affected by nanocomposition. Focusing on the IT-SOFCs, two symmetric cells of the type MOx+LSGF/CGO/LSGF+MOx have been prepared starting from the nanocomposites’ powder. The effect of the SOFCs preparation conditions (temperature, atmosphere) on the electrode and on the cell has been assessed and compared, also through in-situ high temperature XRD, simulating, on the electrodes’ powder, the same treatment necessary to prepare the cell. The use of nanocomposites powders as starting point for electrodes allows to deeply modify the electrochemical performance. A thin, Sr/Fe-rich foil forms on the surface of the electrode during SOFC thermal and deeply improves the electrochemical behaviour of the FeOx+LSGF cathode. The electrochemical results are encouraging for future application in SOFCs, as nanocomposite has an ASR reduced by ⅓ compared to LSGF to 2.1 &#937·cm2 at 620°C.

International audience; A resistive soot sensor for diesel particulate filter (DPF) failure detection was developed in previous works. By measuring the conductance between two Pt electrodes, this sensor is able to detect a low leakage from the DPF but only provides soot mass information. In this study, we have characterized and determined the key parameters that influence the sensor response, i.e. the conductance with the aim to build a model that could provide soot number measurements. First results show a dependency of the sensor response with the soot mass concentration and the polarization level of the electrodes.

International audience; The feasibility of room temperature ammonia gas sensors based on tin dioxide (SnO2) functionalization has been demonstrated. 3-aminopropyltriethoxysilane (APTES) was used as an intermediate step, followed by functionalization with molecules having acyl chloride with different end functional groups molecules such as alkyl, acid and ester groups. Modified films were characterized by attenuated total reflectance infra-red spectroscopy (ATR-FTIR). Upon exposure to ammonia gas, the electrical conductance of alkyl, acid and ester modified SnO2-APTES increases, whereas other reducing gases such as ethanol, carbon monoxide and acetone show no change in conductance. Furthermore, ester modified SnO2 is more selective than acid modified sensor regarding ethanol and carbon monoxide gases

International audience; Air Pollution monitoring and measurement are generally done using sampling techniques and analysis equipment often heavy, complex and expensive. Although these methods offer a high measurement precision which is essential to answer standards requirements, they are not adapted for quality oriented applications where simple information with low precision can be sufficient. The use of semiconductor gas sensors networks can provide the answer for a “low cost” system intended for such applications in air pollution detection fields. Three identical portable autonomous sensors arrays were built, each containing nine commercial semiconductor sensors especially chosen to detect a large range of pollutants usually encountered in ambient air and for a large part of them regulated. In order to overcome the temporal instability and the lack of reproducibility of these sensors, a calibration and normalisation procedure was developed. The obtained systems were used for on-site pollution monitoring in association with the French National Network of Accredited Associations for Air Quality Monitoring (AASQA). Gathered data from sensors systems and network data (NO, NO2, CO, PM2,5, …) were treated using nonlinear regression algorithms like Neural Networks with an original “fuzzy logic” type pre-treatment in order to compute a model able to predict the membership degree for three predefined pollution categories: traffic, urban and photochemical pollution, along with a pollution index describing the severity of the predominant pollution. The prediction rate was estimated system per system, and site per site for six sites. It has been shown that it was possible to obtain a quasi-universal model with a success rate over 80%.

This study reports the electrochemical properties for NOx reduction of a ceria-based mixed ionic electronic conducting porous electrode promoted by Pt nanoparticles, as efficient catalyst for NO oxidation, and BaO, as sorbent to store NOx. This catalytic layer was deposited by screen-printing on a dense membrane of gadolinia-doped ceria, an O2− ionic conductor. The targeted Ba and Pt loadings were 150 and 5 μg/cm2, respectively. The NOx selective electrochemical reduction was performed between 400 °C and 500 °C with and without oxygen in the feed. Variations of the open-circuit voltage with time were found to be a good sensor of the NOx storage process on the ceria-based catalyst-electrode. However, no N2 production was observed in the presence of O2 phase in spite of nitrates formation.

International audience; Printed electronics, particularly on flexible and textile substrates, raised a strong interest during the past decades. This work presents a good candidate for conductive inks based on a graphene/polymer nanocomposite material that gathers three main benefits that are 1 - neither clogging nor flocculation, 2 - spontaneous film formation around room temperature, 3 - high conductivity. Nanosized Multilayered Graphene (NMG) is produced through a solvent-free procedure, using a grinding process in water. These NMG suspensions are used to elaborate conductive composite materials through physical blending with emulsifier-free latex. The nanocomposite microstructure exhibits a well-defined cellular architecture that highlights the formation of continuous paths of fillers throughout the material. The conductivity behavior of the nanocomposite material was efficiently described using a percolation model: the conductivity can be tuned by changing the NMG content and the latex size. A low percolation threshold (0.1 vol%) was obtained and the electrical conductivity reached 217 S m−1 for 6 vol% NMG. Efficient film forming occurs at room temperature leading to continuous and deformable materials, which is adequate for printing on flexible and textile substrates. The applicability in electronics is demonstrated by the use of the nanocomposite material in replacement of copper wires in a LED setup.

International audience; Anode-supported solid oxide fuel cells consisting of nickel-gadolinium doped ceria (NiO-CGO, 60:40 wt%) anode, gadolinium doped ceria (CGO) electrolyte and lanthanum strontium cobaltite ferrite-gadolinium doped ceria (LSCF-CGO) cathode are developed and operated under single-chamber conditions, utilizing methane/air mixture. The cell performance is optimized regarding the electrolyte microstructure, cathode composition and testing conditions. The performance of the cell improves with the decrease of the thickness of the electrolyte and the increase of the ratio of methane to oxygen. The test cell with LSCF-CGO cathode (70:30 wt%) that was sintered at 1100 °C for 2 h and 150 μm dense electrolyte exhibits the maximum power output of ∼260 mW cm−2 at 600 °C in CH4/O2 = 2 atmosphere.

International audience; Since 2011, the Euro 5b European standard limits the particle number (PN) emissions in addition to the particulate mass (PM) emissions. New thermal engine equipped vehicles also have to auto-diagnose their own particulate filter (Diesel particulate filter or gasoil particulate filter) using on-board diagnostic (OBD) sensors. Accumulative resistive soot sensors seem to be good candidates for PM measurements. The aim of this study is to bring more comprehension about soot microstructures construction in order to link the response of such a sensor to particle size and concentration. The sensor sensitivity to the particle size has been studied using successively an electrostatic and an aerodynamic classification, showing the same trend.

A solid oxide fuel cell was designed to be operated in pure methane, without external reforming or carrier gas. The fuel cell was built up from conventional NiO-YSZ anode supported cell with a specific Pt screen-printed anodic collecting system and a Ir-CGO catalytic layer. The operation principle is based on Gradual Internal Reforming. After an initiation in H2 for 30 minutes, the cell was operated for almost 2000 hours in pure and dry CH4 with a fuel utilization rate of 30 %. Intrinsic gradual degradation of 15 %/1000 h was observed, but no coking occurred at the anodic side.

International audience; This 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.

International audience; In the present work, SnO2 sensors were produced by thick film fabrication. In order to deal with well-known lack of selectivity of SnO2 sensors, functionalization was performed. Silanization by 3-aminopropyltriethoxysilane (APTES) in liquid phase was used as an intermediate step, followed by functionalization with molecules bearing acyl chloride with different end functional groups molecules, for example ester group. Modified sensors with APTES and ester end functional group were successfully characterized by attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR). The SnO2 sensor modified with ester end group was found to be sensitive and selective to ammonia gas at 100°C. Working at low temperature is also one of the advantages of these sensors as well as the selectivity with respect to other gases like acetone.

Special session I: sensors for automotive applications; International audience; This study reports on the influence of the polarization applied between platinum electrodes of a soot resistive sensor. The conductance measured between these electrodes represents the sensor response which increases during soot deposition over time at fixed parameters (soot flow, polarization). It is observed that a maximum response is obtained for an optimum polarization. This behaviour is explained by equilibrium between the creation and destruction of inter-electrodes soot bridges.

International audience; This paper concerns tin dioxide gas sensors for automotive exhaust gas application. It consists in elaborating robust sensors on alumina substrate by screen-printing technology. Sensors have been tested on a synthetic gas bench which is able to generate high gas velocity and gases at high temperatures close to real exhaust gas conditions. The responses of the sensors to three gases were modeled, and the classical model of electrical conductivity with one reducing or oxidizing pollutant gas was extended to mixtures. Comparisons between models and experiments are presented with good agreements.

International audience; A 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.

This paper presents a feasibility study on the development of a gas preconcentrator based on micro-reactor technology on silicon. The objectives are to select a gas adsorbent material, to produce a silicon micro-reactor with an integrated heater, and finally to introduce the most suitable adsorbent into the micro-channels of the device. Preliminary results related to the characterization of a carbon adsorbent for the development of a device for the preconcentration of benzene are reported. Carbon nano-powders have been tested as adsorbent material by the determination of the breakthrough time on a dedicated test bench consisting of gas sensors and a non-selective photoionization detector (micro-PID) analyzer. A fluidic deposition process allows filling up the silicon micro-channels with the carbon nano-powder. The interest in using porous silicon to enhance the binding of the carbon nano-particles in the micro-channels was also investigated. A silicon micromachined preconcentrator filled with 0.30 mg of commercial activated charcoal powder (Aldrich, 30-100 nm) was designed and built up. The total capacity of adsorption was determined by using the breakthrough time, which is of 2.2 min under a gas flow of 100 ppm of benzene at 1 l/h. Preliminary tests of preconcentration with 100 and 1.3 ppm benzene in dry air were performed. © 2007 Elsevier B.V. All rights reserved.

International audience; We report on the development of a metal oxide (MOx) sensor prepared by inkjet printing technology onto polyimide foil. Gold electrodes and a gold heater were printed on each side of the substrate, respectively. SnO2 based ink was developed by sol-gel method and printed onto the electrodes. A final annealing at 400 °C compatible with the polymeric transducers allows to synthetize the SnO2 film. Electrical measurements were carried out to characterize the response of fully printed sensor under different gases. The device was operated at a temperature between 200 and 300 °C using the integrated heater. The sensor exhibited responses to carbon monoxide and nitrogen dioxide, under dry and wet air.

International audience; In 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, but in the SC-SOFC configuration it does not play tightness role between compartments. For this reason, the electrolyte can be made by screen printing, a technique particularly appropriate for preparing thick porous layers. However, 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 by a laser treatment. The material chosen for the electrolyte was cerium gadolinium oxide Ce0,9Gd0,1O1,95 (CGO) which is deposited by screen printing on a composite anode NiO-CGO. KrF excimer laser and Yb fiber laser irradiations were used to modify the density of the electrolyte coating. Different tests were performed with the variation of energy density and number of pulses. Microstructural characterizations confirm the densification on the surface of the electrolyte for appropriate experimental conditions. The effect of laser treatment on SC-SOFC performances will also be discussed.

International audience; This paper presents the optimization of a micro gas preconcentrator (μ-GP) system applied to atmospheric pollution monitoring, with the help of a complete modeling of the preconcentration cycle. Two different approaches based on kinetic equations are used to illustrate the behavior of the micro gas preconcentrator for given experimental conditions. The need for high adsorption flow and heating rate and for low desorption flow and detection volume is demonstrated in this paper. Preliminary to this optimization, the preconcentration factor is discussed and a definition is proposed.

SSCI-VIDE+CARE+PVE; International audience; Among various NOx sensors developments, mixed potential sensor based on Yttria Stabilized Zirconia (YSZ) with a simple planar architecture Au/YSZ/Pt is of practical interest. Au composites electrodes were investigated to improve sensing performances. Such potentiometric solid-state gas sensors – were fabricated by screen-printing and tested for NO2 detection. Electrochemical impedance spectroscopy has shown that the addition of YSZ in the Au electrode decreased the polarization resistance in air. In addition, the (Au + 10 wt% YSZ)/YSZ/Pt sensor has a shorter response time and higher sensitivity to NO2 (range 20–100 ppm) at 450–550 °C in comparison with a reference Au/YSZ/Pt sensor. On the other hand, the addition of non-conductive ZrO2 does not significantly modify the electrochemical property but strongly damages the sensor responses toward NO2.

International audience; Conventional screen-printing inks are constituted of the active material, tin oxide in this study, organic and mineral binders. This last constituent is beneficial to the mechanical strength and adhesion of thick films, especially onto micro-hotplates, but is detrimental to the electrical properties required for sensor applications. An innovative solution consists in its replacement by a precursor which is transformed into SnO2 during the thermal annealing of the layers. Inks containing a tin powder, an organic binder and either a gel or an alkoxide as precursor, with various compositions were studied. The organic binder is necessary to adjust the rheological properties of the ink, but it creates porosity and decreases the conductance. The addition of a gel allows to improve electrical properties but complicates ink preparation, and the adhesion remains insufficient. The use of an alkoxide (tin(II) 2-ethylexanoate) at a low content (15 wt.%) combined with the organic binger (24 wt.%) and tin oxide powder promotes both adhesion and conductance. Moreover, the low decomposition temperature of the alkoxide (300 ◦C) allows to decrease the annealing temperature of the layers which reinforces the compatibility of screen-printing with micro-hotplate technology.