Base de description des défauts 2D et 3D pour le diagnostic d'une pile à combustible par la mesure de champ magnétique externe

International audienceL’objectif des travaux actuels consiste à parvenir,par la résolution d’un problème inverse magnétostatique àconstruire la distribution de la densité du courant en 3D àl’intérieur d’une pile à combustible par la mesure non-invasivede champ magnétique externe, ce qui va nous amener à concluresur le changement des propriétés électrochimiques de la pile dansle cas d’un défaut quelconque. Une description de ces défautspermet de poser la démarche à suivre afin de les identifier enconstruisant des bases de projections qui regroupent descombinaisons linéaires de défauts possibles

Solid-state internal reference electrode based on quinhydrone for hydrogen sensor with acid-doped polybenzimidazole

International audienceAn electrode consisting of a mixture of quinhydrone (QH) and polybenzimidazole (PBI) with carbon was investigated as a solid reference electrode for hydrogen sensors. The vibrational behaviour of the polybenzimidazole/quinhydrone blend was investigated by infrared spectroscopy. The results suggest the existence of hydroquinone in the blend. The quinone/hydroquinone redox couple was evidenced by cyclic voltammetry. The potential of the solid-state reference electrode was found to be very stable over a period of 700 h. The drift was less than 0.1 mV per day. This electrode was successfully implemented in a potentiometric sensor. The standard potential was of the order of −550 mV at room temperature and increased as a function of the temperature with a slope of 1 mV/°C. The standard potential was also insensitive to changes in relative humidity (rh) in the sample gas over a period of 1 day

Capteur potentiométrique tout solide pour le dosage de l'hydrogène dans l'air

L'objectif de ce travail était la mise au point d'un capteur potentiométrique tout solide pour le dosage de l'hydrogène dans l'air et la compréhension des mécanismes de réponse.Dans une première partie, le potentiel d'électrodes à diffusion gazeuse, au contact d'un conducteur protonique polymère (polybenzimidazole), a été étudié dans des mélanges hydrogène/gaz inerte et hydrogène/air. Ce travail a permis de valider le modèle de la tension mixte pour expliquer les réponses potentiométriques des capteurs. Il a de plus démontré l'influence de l'humidité sur la tension des capteurs. Un modèle simulant la réponse en tension mixte, dans l'hypothèse d'une limitation par le transport de matière, a enfin été proposé.Dans une seconde partie, une étude de deux systèmes de référence tout solide a été réalisée. Le potentiel de ces deux systèmes, l'un basé sur un sel d'argent et l'autre sur la quinhydrone, est analysé en terme de stabilité et de reproductibilité.GRENOBLE1-BU Sciences (384212103) / SudocTOULON-BU Centrale (830622101) / SudocSudocFranceF

Electrochemical sensors for detection of hydrogen in air: model of the non-Nernstian potentiometric response of platinum gas diffusion electrodes

International audienceThe potentiometric response of three different platinum gas diffusion electrodes deposited on H3PO4 doped polybenzimidazole (PBI) was investigated under humidified atmospheres that contained H2 or mixtures of H2 and O2. Continuum modelling was used to analyse the response. It is shown that the non-Nernstian response under H2—H2O—N2 mixtures can be explained by a difference of water activity on both sides of the membrane. Under H2—O2—N2 mixtures, the oxygen mass transport parameters have a strong effect on the electrode sensitivity

Les systèmes d'électrolyse de l'eau à membrane échangeuse de proton.

International audienceLa production de l'hydrogène par électrolyse de l'eau via une membrane échangeuse de protons est un procédé de conversion électrochimique de l'eau en oxygène et hydrogène grâce à l'application d'un courant électrique. Contrairement à d'autres procédés électrolytiques de production d'hydrogène, comme en milieu alcalin (KOH 6M), ou à haute température (600 ~ 800 °C) avec des électrolytes céramiques, la technologie PEM (pour Proton Membrane Exchange) utilise une membrane polymère qui joue à la fois le rôle de séparateur de gaz et d'électrolyte. Dans cet article seront abordés les principes de fonctionnement et l'architecture classique des électrolyseurs PEM, leurs performances actuelles et les travaux de recherche et de développement visant à les améliorer

Les systèmes d'électrolyse de l'eau à membrane échangeuse de proton.

International audienceLa production de l'hydrogène par électrolyse de l'eau via une membrane échangeuse de protons est un procédé de conversion électrochimique de l'eau en oxygène et hydrogène grâce à l'application d'un courant électrique. Contrairement à d'autres procédés électrolytiques de production d'hydrogène, comme en milieu alcalin (KOH 6M), ou à haute température (600 ~ 800 °C) avec des électrolytes céramiques, la technologie PEM (pour Proton Membrane Exchange) utilise une membrane polymère qui joue à la fois le rôle de séparateur de gaz et d'électrolyte. Dans cet article seront abordés les principes de fonctionnement et l'architecture classique des électrolyseurs PEM, leurs performances actuelles et les travaux de recherche et de développement visant à les améliorer

Evolution during accelerated stress test of performance and ionomer catalyst layer physical and chemical structures in Proton Exchange Membrane Fuel Cell

International audienceCatalyst layers ionomer plays a crucial role in the operation of Proton Exchange Membrane Fuel Cell (PEMFC) not simply because it binds the catalyst nanopowder but mostly because it allows protons transport and affects both gas diffusivity and water management. In the catalyst layer, the ionomer is a perfluorosulfonic acid polymer similar to that use in the membrane as electrolyte. It is in the form of a few nanometer thick film dispersed around the carbon support or as aggregates larger than 150 nm within the pores of the carbon network . In contrast with bulk ionomer membrane or model thin films that have been extensively studied, little is known on the structural and functional properties of this proton conducting ionomer inside the electrode, and even less on their evolution upon aging. To date, it has proven difficult to selectively probe the fluorinated polymer dispersed at the nanoscale in a few micrometer thick electrode using conventional laboratory characterization techniques (electrochemistry, spectroscopy, and microscopy). Especially, its evolution upon aging is still an open question whereas the degradation of the ionomer due to radical attack was demonstrated and extensively investigated. Only Morawietz and co-workers evidence a thinning of the ionomer after operationIn this study, we studied the evolution of performance of a Membrane Electrode Assembly (MEA) after Accelerated Stress Test (AST) known to induce severe membrane degradation due to radicals, as well as the physical and chemical structures of the ionomer in the catalyst layer. Small Angle Neutron Scattering (SANS) spectra have been extensively analysed to characterise its swelling behaviour as a function of relative humidity. Its chemical structure was investigated by elemental analyses and XPS measurements, in addition to measurements of ion exchange capacity and of vapour sorption isotherms. Electrochemical characterisations including polarisation curve, impedance measurements and limiting current analyses in dry and wet conditions were performed to assess limiting phenomena and to try to unravel the contribution of the ionomer properties in the loss of performance. The SANS measurements clearly evidence an evolution of the structure and swelling behaviour of the ionomer after AST but, despite multiple characterisations, they can be hardly related to the evolution of electrochemical characteristic

Evolution during accelerated stress test of performance and ionomer catalyst layer physical and chemical structures in Proton Exchange Membrane Fuel Cell

International audienceCatalyst layers ionomer plays a crucial role in the operation of Proton Exchange Membrane Fuel Cell (PEMFC) not simply because it binds the catalyst nanopowder but mostly because it allows protons transport and affects both gas diffusivity and water management. In the catalyst layer, the ionomer is a perfluorosulfonic acid polymer similar to that use in the membrane as electrolyte. It is in the form of a few nanometer thick film dispersed around the carbon support or as aggregates larger than 150 nm within the pores of the carbon network . In contrast with bulk ionomer membrane or model thin films that have been extensively studied, little is known on the structural and functional properties of this proton conducting ionomer inside the electrode, and even less on their evolution upon aging. To date, it has proven difficult to selectively probe the fluorinated polymer dispersed at the nanoscale in a few micrometer thick electrode using conventional laboratory characterization techniques (electrochemistry, spectroscopy, and microscopy). Especially, its evolution upon aging is still an open question whereas the degradation of the ionomer due to radical attack was demonstrated and extensively investigated. Only Morawietz and co-workers evidence a thinning of the ionomer after operationIn this study, we studied the evolution of performance of a Membrane Electrode Assembly (MEA) after Accelerated Stress Test (AST) known to induce severe membrane degradation due to radicals, as well as the physical and chemical structures of the ionomer in the catalyst layer. Small Angle Neutron Scattering (SANS) spectra have been extensively analysed to characterise its swelling behaviour as a function of relative humidity. Its chemical structure was investigated by elemental analyses and XPS measurements, in addition to measurements of ion exchange capacity and of vapour sorption isotherms. Electrochemical characterisations including polarisation curve, impedance measurements and limiting current analyses in dry and wet conditions were performed to assess limiting phenomena and to try to unravel the contribution of the ionomer properties in the loss of performance. The SANS measurements clearly evidence an evolution of the structure and swelling behaviour of the ionomer after AST but, despite multiple characterisations, they can be hardly related to the evolution of electrochemical characteristic

Insights into the ionomer structure contained in PEMFC electrodes with Small Angle Neutron Scattering

International audienc

Insights into the ionomer structure contained in PEMFC electrodes with Small Angle Neutron Scattering

International audienc