Letteratura scientifica selezionata sul tema "Membrane d’échangeuse de protons"
Cita una fonte nei formati APA, MLA, Chicago, Harvard e in molti altri stili
Consulta la lista di attuali articoli, libri, tesi, atti di convegni e altre fonti scientifiche attinenti al tema "Membrane d’échangeuse de protons".
Accanto a ogni fonte nell'elenco di riferimenti c'è un pulsante "Aggiungi alla bibliografia". Premilo e genereremo automaticamente la citazione bibliografica dell'opera scelta nello stile citazionale di cui hai bisogno: APA, MLA, Harvard, Chicago, Vancouver ecc.
Puoi anche scaricare il testo completo della pubblicazione scientifica nel formato .pdf e leggere online l'abstract (il sommario) dell'opera se è presente nei metadati.
Articoli di riviste sul tema "Membrane d’échangeuse de protons"
1
Sokolov, Valerij S., Vsevolod Yu Tashkin, Darya D. Zykova, Yulia V. Kharitonova, Timur R. Galimzyanov e Oleg V. Batishchev. "Electrostatic Potentials Caused by the Release of Protons from Photoactivated Compound Sodium 2-Methoxy-5-nitrophenyl Sulfate at the Surface of Bilayer Lipid Membrane". Membranes 13, n. 8 (8 agosto 2023): 722. http://dx.doi.org/10.3390/membranes13080722.
Testo completoAbstract (sommario):
Lateral transport and release of protons at the water–membrane interface play crucial roles in cell bioenergetics. Therefore, versatile techniques need to be developed for investigating as well as clarifying the main features of these processes at the molecular level. Here, we experimentally measured the kinetics of binding of protons released from the photoactivated compound sodium 2-methoxy-5-nitrophenyl sulfate (MNPS) at the surface of a bilayer lipid membrane (BLM). We developed a theoretical model of this process describing the damage of MNPS coupled with the release of the protons at the membrane surface, as well as the exchange of MNPS molecules and protons between the membrane and solution. We found that the total change in the boundary potential difference across the membrane, ∆ϕb, is the sum of opposing effects of adsorption of MNPS anions and release of protons at the membrane–water interface. Steady-state change in the ∆ϕb due to protons decreased with the concentration of the buffer and increased with the pH of the solution. The change in the concentration of protons evaluated from measurements of ∆ϕb was close to that in the unstirred water layer near the BLM. This result, as well as rate constants of the proton exchange between the membrane and the bulk solution, indicated that the rate-limiting step of the proton surface to bulk release is the change in the concentration of protons in the unstirred layer. This means that the protons released from MNPS remain in equilibrium between the BLM surface and an adjacent water layer.
2
Ababneh, Omar, Abdallah Barjas Qaswal, Ahmad Alelaumi, Lubna Khreesha, Mujahed Almomani, Majdi Khrais, Oweiss Khrais et al. "Proton Quantum Tunneling: Influence and Relevance to Acidosis-Induced Cardiac Arrhythmias/Cardiac Arrest". Pathophysiology 28, n. 3 (3 settembre 2021): 400–436. http://dx.doi.org/10.3390/pathophysiology28030027.
Testo completoAbstract (sommario):
Acidosis and its associated pathologies predispose patients to develop cardiac arrhythmias and even cardiac arrest. These arrhythmias are assumed to be the result of membrane depolarization, however, the exact mechanism of depolarization during acidosis is not well defined. In our study, the model of quantum tunneling of protons is used to explain the membrane depolarization that occurs during acidosis. It is found that protons can tunnel through closed activation and inactivation gates of voltage-gated sodium channels Nav1.5 that are present in the membrane of cardiac cells. The quantum tunneling of protons results in quantum conductance, which is evaluated to assess its effect on membrane potential. The quantum conductance of extracellular protons is higher than that of intracellular protons. This predicts an inward quantum current of protons through the closed sodium channels. Additionally, the values of quantum conductance are influential and can depolarize the membrane potential according to the quantum version of the GHK equation. The quantum mechanism of depolarization is distinct from other mechanisms because the quantum model suggests that protons can directly depolarize the membrane potential, and not only through indirect effects as proposed by other mechanisms in the literature. Understanding the pathophysiology of arrhythmias mediated by depolarization during acidosis is crucial to treat and control them and to improve the overall clinical outcomes of patients.
3
Weichselbaum, Ewald, e Peter Pohl. "Protons at the membrane water interface". Biochimica et Biophysica Acta (BBA) - Bioenergetics 1859 (settembre 2018): e117. http://dx.doi.org/10.1016/j.bbabio.2018.09.346.
Testo completo
4
Rayabharam, Archith, e N. R. Aluru. "Quantum water desalination: Water generation through separate pathways for protons and hydroxide ions in membranes". Journal of Applied Physics 132, n. 19 (21 novembre 2022): 194302. http://dx.doi.org/10.1063/5.0122324.
Testo completoAbstract (sommario):
Much of the water desalination strategies has focused on designing pores and membranes that transport water and reject ions and other molecules at a high rate. In this paper, we discuss an approach where protons (H+) and hydroxide (OH−) ions are transported via different mechanisms through a porous membrane, and subsequently, once they have been transported through the membrane, they recombine to generate water. 2D materials such as graphene and MoS2 have generated significant interest for applications such as desalination. Here, we explore the applicability of one such 2D material—a cubic Ti2C MXene membrane—in desalination by creating a OH− ion selective pore, which significantly suppresses protons but allows OH− ions and water to go through. The catalytic properties of MXenes enable the dissociation of water on the surface, and the dissociated protons translocate through the membrane via quantum-dominated phenomena such as hopping from interstitial-to-interstitial. OH− ions translocate through a positively charged pore and recombine with protons on the other side of the membrane to form water. Our results indicate that water molecules generated via quantum processes can significantly enhance the overall transport of water across the membrane.
5
Bramhall, John. "Conductance routes for protons across membrane barriers". Biochemistry 26, n. 10 (maggio 1987): 2848–55. http://dx.doi.org/10.1021/bi00384a028.
Testo completo
6
Abdallat, Mahmoud, Abdallah Barjas Qaswal, Majed Eftaiha, Abdel Rahman Qamar, Qusai Alnajjar, Rawand Sallam, Lara Kollab et al. "A mathematical modeling of the mitochondrial proton leak via quantum tunneling". AIMS Biophysics 11, n. 2 (2024): 189–233. http://dx.doi.org/10.3934/biophy.2024012.
Testo completoAbstract (sommario):
<abstract> <p>The mitochondrion is a vital intracellular organelle that is responsible for ATP production. It utilizes both the concentration gradient and the electrical potential of the inner mitochondrial membrane to drive the flow of protons from the intermembrane space to the matrix to generate ATP via ATP-synthase. However, the proton leak flow, which is mediated via the inner mitochondrial membrane and uncoupling proteins, can reduce the efficiency of ATP production. Protons can exhibit a quantum behavior within biological systems. However, the investigation of the quantum behavior of protons within the mitochondria is lacking particularly in the contribution to the proton leak. In the present study, we proposed a mathematical model of protons tunneling through the inner mitochondrial membrane and the mitochondrial carrier superfamily MCF including uncoupling proteins UCPs and the adenine nucleotide translocases ANTs. According to the model and its assumptions, the quantum tunneling of protons may contribute significantly to the proton leak if it is compared with the classical flow of protons. The quantum tunneling proton leak may depolarize the membrane potential, hence it may contribute to the physiological regulation of ATP synthesis and reactive oxygen species ROS production. In addition to that, the mathematical model of proton tunneling suggested that the proton-tunneling leak may depolarize the membrane potential to values beyond the physiological needs which in turn can harm the mitochondria and the cells. Moreover, we argued that the quantum proton leak might be more energetically favorable if it is compared with the classical proton leak. This may give the advantage for quantum tunneling of protons to occur since less energy is required to contribute significantly to the proton leak compared with the classical proton flow.</p> </abstract>
7
Keller, David, Seema Singh, Paola Turina, Roderick Capaldi e Carlos Bustamante. "Structure of ATP synthase by SFM and single-particle image analysis". Proceedings, annual meeting, Electron Microscopy Society of America 53 (13 agosto 1995): 722–23. http://dx.doi.org/10.1017/s0424820100139986.
Testo completoAbstract (sommario):
F1Fo ATP synthases are the proteins responsible for the synthesis of ATP in oxidative phosphorylation, and are present in some form in all aerobic organisms, both prokaryotic and eukaryotic. They use the energy stored in a transmembrane proton gradient (which is generated by other members of the oxidative phosphorylation pathway) to synthesize ATP from ADP and Pi or, working in reverse, to pump protons across the membrane using the energy of ATP hydrolysis. The full protein has two sectors, F1 and Fo. F1 is normally bound to Fo (which is membrane integrated), but is water soluble when dissociated. The F1 sector contains the sites which bind ADP and catalyze its conversion to ATP. The Fo sector contains a channel which allows protons to to cross the membrane, dissipating the transmembrane chemical potential. By an unknown mechanism this translocation of protons through Fo is coupled to the hydrolysis or synthesis of ATP in F1, so that the energy released in hydrolysis of ATP can drive the motion of protons against an electrochemical potential, or the energy of translocating protons can be used to form high energy ADP-Pi bonds.
8
M., Ambaga, Tumen-Ulzii A. e Buyantushig T. "THE BUFFERING CAPACITY OF ERYTHROCYTE MEMBRANE SURROUNDINGS IN RELATION TO FREE PROTONS INSIGHTOF NEW ELUCIDATION OF EIGTH AND NINTH STAGES OF THE MEMBRANE REDOXY POTENTIAL THREE STATE DEPENDENT 9 STEPPED FULL CYCLE OF PROTON CONDUCTANCE IN THE HUMAN BODY". International Journal of Advanced Research 10, n. 11 (30 novembre 2022): 29–33. http://dx.doi.org/10.21474/ijar01/15638.
Testo completoAbstract (sommario):
It was became clear that the flow-fate of all many many protons,generated in mitochondria of 50-80 trillion cells (now by us mitochondria flow of protons named as 1-7 stages of proton conductance) have been needed another special structures - another system needs to soak up the extra H+ activity generated as a result of process conducted in the 1-7 stages of proton conductance in order for true buffering to occur, that system consists of intracellular proteins, of which haemoglobin is the key player, concretely speaking,one of these are the erythrocyte membrane surroundings for packaging of protons and alsoHydrochloric acid formationby Gastric parietal cells,also H+/Na antiport in the membrane transports H+ out of cell and Na ion in the level of Peritubular capillary-Interstitial fluid-Tubule epithelial cells-Tubular fluid with accompanying maintaining of serum and cell pH-7,4.By our suggestion, the buffering capacity of erythrocyte membrane surroundings in relation to free protons, formed in the proton conductance have implemented within Ninth stage -located in the Respiratory membrane, Pulmonary circuit, where occurred oxygen uptake from alveolar air under effect of increased bicarbonate entry by bicarbonate/chloride ion shift mechanism, leading to increase of HbO2 formation, resulting to release of proton,electron from food substrates under the undirect action of oxygen released from membrane surroundings of erythrocyte in the 8-th stage of proton conductance.
9
Kluka, Ľubomír, Ernest Šturdík, Štefan Baláž, Dušan Kordík, Michal Rosenberg, Marián Antalík e Jozef Augustín. "Membrane proton transport mediated by phenylhydrazonopropanedinitriles". Collection of Czechoslovak Chemical Communications 53, n. 1 (1988): 186–97. http://dx.doi.org/10.1135/cccc19880186.
Testo completoAbstract (sommario):
Some fundamental physicochemical characteristics as stability in solutions, solubility in various solvents and association constants describing equilibria with protons and potassium ions in aqueous solutions were determined for phenylhydrazonopropanedinitriles (PHPD). The effect of pH and sodium, potassium, calcium, and magnesium cations on the distribution of PHPD were examined in a two-compartment system 1-octanol-water. The transmembrane transfer of protons by PHPD causing a disturbance of the pH-gradient was verified in vitro using a model three-compartment system water-octanol-water, imitating the in vivo intracristal space-inner mitochondrial membrane – matrix system. Transfer of H+ ions mediated by PHPD in the system under study was found to be considerably faster when an exchange with K+ ions (ion-exchanging antiport H+/K+) was possible. A model was described indicating the reality of ion-exchanging antiport H+/Me+ mediated by PHPD on biomembranes which is in line with the chemiosmotic theory.
10
Vidilaseris, Keni, Juho Kellosalo e Adrian Goldman. "A high-throughput method for orthophosphate determination of thermostable membrane-bound pyrophosphatase activity". Analytical Methods 10, n. 6 (2018): 646–51. http://dx.doi.org/10.1039/c7ay02558k.
Testo completoAbstract (sommario):
Membrane-bound pyrophosphatases (mPPases) are homodimeric integral membrane proteins that hydrolyse pyrophosphate into orthophosphates coupled to the active transport of protons or sodium ions across membranes.
Tesi sul tema "Membrane d’échangeuse de protons"
1
Ebrahimi, Mohammad. "Hybrid membranes based on iοnic liquids for application in fuel cells". Electronic Thesis or Diss., Normandie, 2024. http://www.theses.fr/2024NORMR029.
Testo completoAbstract (sommario):
La pile à combustible à membrane échangeuse de protons (PEMFC) suscite beaucoup d’intérêts dans le milieu académique et dans l’industrie, puisqu’ elle est considérée comme une source d’énergie verte. La membrane électrolytique polymère (PEM), responsable du transport des protons entres les électrodes, est la partie la plus importante de la PEMFC. Le Nafion® est le polymère le plus couramment utilisé en tant que PEM du fait de ses bonnes stabilités thermique, mécanique et chimique ainsi qu'une conductivité ionique élevée. Ce polymère présente d’excellentes performances à des températures inférieures à 80 °C et dans les conditions humidifiées. Cependant, pour augmenter la vitesse de la réaction et éviter l’empoisonnement du Pt, l’utilisation de la PEMFC à des températures élevées est recommandée. En revanche, dans ces conditions, la conductivité ionique de Nafion® diminue considérablement en raison de sa déshydratation Pour obtenir des PEMs pouvant être utilisées à des températures élevées et dans des conditions anhydres, des liquides ioniques (LIs) jouant le rôle de conducteurs protoniques sont envisagés. L’objectif de cette thèse était de synthétiser des nouveaux LIs thermiquement stables et conducteurs et de les utiliser comme agent de transport pour concevoir des membranes conductrices de protons pour une application PEMFC à température élevée.Plusieurs LIs protiques (LIs-Pr) contenant différents anions ([TFS]-, [TFA]-, [HS]-, [BUPH]- et [EHPH]) et cations ([DETA]-, [DEPA]-, [MIM]- et [BIM]) ont été synthétisés via une réaction de neutralisation acido-basique. Les résultats d’analyse thermogravimétrique ont montré qu’il existe un lien direct entre l’acidité de l’acide utilisé et la stabilité thermique du LI – les LIs à base de [TFS] présentent les plus grandes stabilités thermiques (Tdeg ~ 415−435 °C) étant donné l’acidité élevée de l’acide trifluorométhanesulfonique (pKa ~ -14). Les valeurs de conductivité ionique les plus élevées (~ 34.5 à 63.7 mS•cm-1 à 150 °C) ont été obtenues pour les LIs à base de [TFS], du fait du caractère plus acide de du TFS par rapport aux autres acides. D’après les données expérimentales, l’ordre de conductivité ionique est le suivant : [TFS] ˃ [HS] ˃ [TFA] ˃ [BUPH] ˃ [EHPH]. L’ensemble des résultats obtenus confirment que les LIs-Pr synthétisées ont un fort potentiel pour le développement des PEMFC. Cependant, en raison de l’état physique des LIs (solide dans la plupart des cas), il n’est pas possible de les utiliser comme électrolyte directement dans les PEMFC. Ce verrou peut-être levé par la mise au point de PEM à partir de membranes composites (polymère + LI).Les membranes composites à base de CAB/[DETA][TFS]-[DEPA][BUPH] (0, 23, 33 et 41 % en poids de LI – M0, M1, M2 et M3, respectivement) ont été préparées par une technique d’inversion de phase. La présence de LI dans la structure membranaire a été confirmée par les analyses IRTF et Rayons-X. L’analyse thermogravimétrique a permis de vérifier une stabilité thermique inférieure pour les membranes composites (Tdeg ~ 256–265 °C) par rapport à la membrane CAB pure (Tdeg ~ 360 °C). Des mesures d’impédance il résulte que les membranes composites possèdent une bonne conductivité ionique (0.1–1 mS•cm-1 à 120 °C). Comme attendu, l’augmentation de la proportion massique de LI de 23 à 41 % dans la membrane a conduit à une augmentation de la conductivité ionique des membranes composites. Aussi une augmentation de la conductivité ionique de la membrane liée à l’augmentation la température de fonctionnement (de 25 à 120 °C) a été vérifiée en raison de l’amélioration de la mobilité ionique. La membrane M3 a présenté la conductivité ionique la plus élevée – soit 0.443 mS•cm-1 à 120 °C dans des conditions anhydres. Tous les résultats obtenus attestent que les membranes composites à base de CAB/[DETA][TFS]-[DEPA][BUPH] sont des candidats prometteurs pour une utilisation dans des applications électrochimiques, notamment dans les piles à combustibleProton exchange membrane fuel cell (PEMC) has attracted a lot of attention in the both, laboratories and industries because PEMFC is considered as the green source of energy. Polymer electrolyte membrane (PEM) is the most important part in PEMFC owing to the fact that it is responsible for carrying protons between electrodes. Nafion® is the most commonly used polymer for PEM preparation because of its good thermal, mechanical, and chemical stability as well as high ionic conductivity. This polymer has excellent performance at low up to moderate temperatures under humidified condition. However, working at elevated temperature is more desirable and under these conditions the ionic conductivity of Nafion® membrane drops down significantly owing to the water evaporation. To obtain PEMs which can be applied at higher temperatures under anhydrous conditions, ionic liquids (ILs) are used as the proton carrier. The aim of this PhD thesis was to synthesis thermally stable and conductive ILs and use them as the additive to prepare proton conductive membranes for PEMFC application at elevated temperature.Several Pr-ILs containing different anions ([TFS]-, [TFA]-, [HS]-, [BUPH]-, and [EHPH]-based) and cations ([DETA]-, [DEPA]-, [MIM]-, and [BIM]-based) were prepared by acid-base neutralization reaction. The dynamic TGA results showed that there is a direct link between the acidity of acid and thermal stability of IL and [TFS]-based ILs demonstrated the highest thermal stability (Tdeg ~ 415−435 °C) owing to the high acidity of trifluoromethanesulfonic acid (pKa ~ -14). [TFS]-based ILs showed the highest ionic conductivity values (~ 34.5−63.7 mS•cm-1 at 150 °C) because trifluoromethanesulfonic acid is a stronger acid as compared to the other used acids for IL synthesis. According to the results, the following ionic conductivity order of studied anions can be proposed: [TFS] ˃ [HS] ˃ [TFA] ˃ [BUPH] ˃ [EHPH]. The obtained results showed that synthesized Pr-ILs have great potential to be used in PEMFC application. However, owing to the physical state of ILs, it is not possible to use them alone as the electrolyte in PEMFC. In order to have ion conductive PEM, composite membranes (polymer + IL) must be prepared.CAB/[DETA][TFS]-[DEPA][BUPH] composite membranes were prepared by a phase inversion technique. Composite membranes containing 0, 23, 33, and 41 wt.% of ILs were prepared (M0, M1, M2, and M3, respectively) by the phase inversion method. The presence of ILs in the membrane was confirmed by FTIR and EDX analysis. Thermal analysis revealed the lower thermal stability of composite membranes (Tdeg ~ 256–265 °C) in comparison with pure CAB membrane (Tdeg ~ 360 °C). Composite membranes showed good ionic conductivity (0.1–1 mS•cm-1 at 120 °C) and it was found that an increase of ILs concentration from 23 to 41 wt.% resulted in rising the membrane ionic conductivity owing to the increase of conductive regions. Furthermore, membrane ionic conductivity increased by rising the operating temperature from 25 to 120 °C owing to the ionic mobility enhancement. M3 membrane showed the highest ionic conductivity of 0.443 mS•cm-1 at 120 °C under anhydrous condition. The results prove that the fabricated CAB/[DETA][TFS]-[DEPA][BUPH] composite membranes are promising candidates for using in electrochemical applications, namely fuel cell
2
Nabil, Yannick. "Supports de Catalyseur Nanostructurés pour Pile à Combustible à Membrane Échangeuse de Protons". Thesis, Montpellier, Ecole nationale supérieure de chimie, 2015. http://www.theses.fr/2015ENCM0029/document.
Testo completoAbstract (sommario):
La durabilité des piles à combustible à membrane échangeuse de proton (PEMFC) est un des verrous technologiques majeurs qui freinent leurs implantations sur le marché. Ces travaux de thèse s’inscrivent dans ce contexte en proposant l’élaboration de matériaux en carbure de niobium comme support de catalyseur pour remplacer les supports carbonés actuellement utilisés dans les cathodes de PEMFC. Notre démarche est d’associer cette composition à différentes morphologies contrôlées pour développer des matériaux conducteurs, présentant une porosité adaptée et chimiquement plus stable que le carbone qui se corrode dans les conditions de fonctionnement des PEMFC. Ainsi trois voies de synthèse basées sur des techniques variées (filage électrostatique, synthèse hydrothermal avec agent structurant) ont été étudiées aboutissant à trois types de morphologie : des poudres nanostructurées, des tissus nanofibreux et des nanotubes aux parois poreuses. Après leurs caractérisations structurales et morphologiques approfondies, ces supports ont été catalysés avec des nanoparticules de platine synthétisées par une méthode polyol assisté par micro-onde. La finalité de ce projet est d’évaluer les performances électrochimiques relatives à la réaction de réduction de l’oxygène de ces supports catalysés pour mettre en avant leurs exceptionnelles stabilités comparées à un support catalysé de référence (Pt/C) sans perte significative d’activité catalytiqueOne pivotal issue to be overcome for the widespread adoption of Proton exchange membrane fuel cells (PEMFC) is the stability overtime. In this context, This PhD project focuses on the elaboration of niobium carbide based electrocatalyst supports for the PEMFC cathode to replace the conventional carbon based supports that notoriously suffer from corrosion in fuel cell operating conditions. The approach is to associate this alternative chemical composition with controlled morphologies in order to design electronically conductive and chemically stable materials with the appropriate porosity. Three different syntheses involving hydrothermal template synthesis or electrospinning have been developed leading to three different morphologies: nanostructured powders with high surface area, self-standing nanofibrous mats, and nanotubes with porous walls. These various supports have been catalysed by deposition of platinum nanoparticles synthesised by a microwave-assisted polyol method, and they have been characterised for their chemical and structural composition, morphology, and electrochemical properties. This work demonstrates that the Pt loaded NbC supports feature a greater electrochemical stability than a commercial Pt/C reference and similar electrocatalytic activities towards the oxygen reduction reaction
3
Ion, Mihaela Florentina. "Proton transport in proton exchange membrane fuel cells /". free to MU campus, to others for purchase, 2004. http://wwwlib.umi.com/cr/mo/fullcit?p3164514.
Testo completo
4
SANTORO, THAIS A. de B. "Estudo tecnologico de celulas a combustivel experimentais a membrana polimerica trocadora de protons". reponame:Repositório Institucional do IPEN, 2004. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11174.
Testo completoAbstract (sommario):
Made available in DSpace on 2014-10-09T12:49:10Z (GMT). No. of bitstreams: 0Made available in DSpace on 2014-10-09T14:00:37Z (GMT). No. of bitstreams: 1 09831.pdf: 4253435 bytes, checksum: c758abc7c04ca544bdc0f231316160f0 (MD5)
Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
5
Cognard, Gwenn. "Electrocatalyseurs à base d’oxydes métalliques poreux pour pile à combustible à membrane échangeuse de protons". Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAI007.
Testo completoAbstract (sommario):
Les électrocatalyseurs conventionnels utilisés dans les piles à combustibles à membrane échangeuse de protons (PEMFC) sont composés de nanoparticules de platine supportées sur des noirs de carbone de forte surface spécifique. A la cathode de la PEMFC, siège de la réaction de réduction de l’oxygène (ORR), le potentiel électrochimique peut atteindre des valeurs élevées - notamment lors de phases arrêt-démarrage - engendrant des dégradations irréversibles du support carboné. Une solution « matériaux » consiste à remplacer ce dernier par des supports à base d’oxydes métalliques. Ceux-ci doivent être résistants à la corrosion électrochimique, conducteurs électroniques et posséder une structure poreuse et nano-architecturée (permettant le transport des réactifs et produits et une distribution homogène de l’ionomère et des nanoparticules de platine). Dans ce travail, nous avons donc élaboré et caractérisé des électrocatalyseurs à base de nanoparticules de platine (Pt) déposées sur du dioxyde d’étain (SnO₂) et de titane (TiO₂) texturés (morphologies aérogel, nanofibres ou « loosetubes ») et conducteurs électroniques (dopés au niobium Nb ou à l’antimoine Sb). Le support permettant d’atteindre les meilleures propriétés électrocatalytiques est un aérogel de SnO₂ dopé à l’antimoine, noté ATO. En particulier, l’électrocatalyseur Pt/ATO présente une activité spécifique vis-à-vis de l’ORR supérieure à celle d’un électrocatalyseur Pt/carbone Vulcan® synthétisé dans les mêmes conditions, suggérant des interactions bénéfiques entre les nanoparticules de Pt et le support oxyde métallique (Strong Metal Support Interactions, SMSI).Des tests de durabilité simulant le fonctionnement d’une PEMFC en conditions automobile ont été effectués en électrolyte liquide à 80 °C sur ces deux électrocatalyseurs : cyclage entre 0,60 et 1,00 V vs l’électrode réversible à hydrogène (RHE) ou entre 1,00 et 1,50 V vs RHE. Le catalyseur Pt/ATO présente une durabilité accrue par rapport au catalyseur Pt/carbone Vulcan® de référence. Cependant, de nouveaux mécanismes de dégradation ont été mis en évidence dans cette étude : tout d’abord, l’élément dopant Sb est progressivement dissout au cours du vieillissement électrochimique, ce qui implique une perte de conductivité électronique. Cette perte est en partie liée à des incursions à bas potentiel, notamment durant les caractérisations électrochimiques. De plus, entre 5 000 et 10 000 cycles de vieillissement électrochimique (entre 0,60 et 1,00 V vs RHE ou entre 1,00 et 1,50 V vs RHE à 57 °C), le matériau support perd sa structure poreuse et forme un film amorphe peu conducteurConventional electrocatalysts used in proton exchange membrane fuel cells (PEMFC) are composed of platinum nanoparticles supported on high specific surface area carbon blacks. At the cathode side of the PEMFC, where the oxygen reduction reaction (ORR) occurs, the electrochemical potential can reach high values - especially during startup-shutdown operating conditions - resulting in irreversible degradation of the carbon support. A “material” solution consists of replacing the carbon with supports based on metal oxides. The latter have to be resistant to electrochemical corrosion, be electronic conductor and have a porous and nano-architectural structure (for the transport of reagents and products and the homogeneous distribution of the ionomer and platinum nanoparticles).In this work, we have developed and characterized electrocatalysts composed of platinum (Pt) nanoparticles based on tin dioxide (SnO2) and titanium dioxide (TiO2) with optimized textural (aerogel, nanofibres or loosetubes morphologies) and electron-conduction properties (doped with niobium Nb or antimony Sb). The best electrocatalytic properties are reached for an antimony-doped SnO2 aerogel support, denoted ATO. The Pt/ATO electrocatalyst has especially a higher specific activity for the ORR than a Pt/carbon Vulcan® electrocatalyst, synthesized in the same conditions, suggesting beneficial interactions between the Pt nanoparticles and the metal oxide support (Strong Metal Support Interactions SMSI).Durability tests simulating automotive operating conditions of a PEMFC were carried out in liquid electrolyte at 57 °C on these two electrocatalysts by cycling between 0.60 and 1.00 V vs the reversible hydrogen electrode (RHE) or between 1.00 and 1.50 V vs RHE. The Pt/ATO electrocatalyst has an increased stability compared to the reference Pt/carbon Vulcan® electrocatalyst. However, new degradation mechanisms were highlighted in this study: first, the doping element (Sb) is progressively dissolved during electrochemical ageing, which implies a loss of electronic conductivity. This loss is partly due to incursions at low potential, including during electrochemical characterizations. Moreover, between 5,000 and 10,000 cycles of the accelerated stress tests (between 0.60 and 1.00 V vs RHE or between 1.00 and 1.50 V vs RHE at 57 °C), the support loses its porous structure and forms a poorly conductive amorphous film
6
Bultel, Yann. "Modélisation des couches actives d'électrodes volumiques de piles à combustible à membrane échangeuse de protons". Grenoble INPG, 1997. http://www.theses.fr/1997INPG0054.
Testo completoAbstract (sommario):
Ce travail est focalise sur la modelisation des transports de matiere, de charge et de chaleur dans les couches actives des electrodes volumiques de piles a combustible a membrane echangeuse de protons (p. E. M. F. C). Un premier temps decrit la structure des piles a combustible et les processus physico-chimiques aux electrodes sont decrits. Une analyse des modeles classiques rencontres dans la litterature montre qu'ils supposent tous que l'electrocatalyseur est uniformement reparti sur un plan ou en volume. Dans un deuxieme temps, la modelisation des phenomenes de transport de matiere et de charge a ete menee en utilisant un logiciel de calcul numerique (flux-expert#) mettant en oeuvre la methode des elements finis et qui permet de prendre en compte la repartition discrete du catalyseur en nano-particules. Les simulations ont mis en evidence les limitations du taux d'utilisation du catalyseur par la diffusion et la chute ohmique ionique non seulement a l'echelle de la couche d'electrolyte mais aussi a celle des particules. Afin d'ameliorer la modelisation des piles a combustible a membrane echangeuses de protons, les modeles classiques ont ete modifies afin de les rendre capables de prendre en compte ces contributions locales ; ils ne requierent que des methodes numeriques simples telle que celle des differences finies. Appliques a la reduction de l'oxygene a la cathode ou a l'oxydation de l'hydrogene a l'anode, ces modeles permettent de determiner les parametres cinetiques (densites de courant d'echanges et pentes des droites de tafel) corrigees de la diffusion dans la couche active. Une modelisation des transferts thermiques a l'echelle des couches actives est ensuite proposee. Le modele prend en compte les echanges de chaleur convectifs entre les phases solides et le gaz, le transport d'eau par electro-osmose, la creation de chaleur par effet joule et par les reactions electrochimiques. Enfin, le dernier chapitre presente une etude des mecanismes reactionnels dans le cas des electrodes poreuses par la methode des impedances. Des modeles analytiques et numeriques ont ete developpes pour calculer les impedances d'electrode et sont appliques a l'etude de la reduction de l'oxygene et d'oxydation de l'hydrogene.
7
Toudret, Pierre. "Compréhension et optimisation des couches actives de pile à combustible à membrane échangeuse de protons". Electronic Thesis or Diss., Université Grenoble Alpes, 2023. http://www.theses.fr/2023GRALI124.
Testo completoAbstract (sommario):
La pile à combustible à membrane échangeuse de protons (PEMFC) est un convertisseur électrochimique qui produit un courant électrique, de la chaleur et de l'eau à partir de l'oxydation de l'hydrogène et de la réduction de l'oxygène. Cette technologie performante et non émettrice d'émissions de gaz à effet de serre est un candidat prometteur pour réduire les émissions de CO2, en particulier dans les applications de transport lourd (camion, bus, ...). Les couches actives sont le siège des réactions électrochimiques et donc les électrodes de la PEMFC. Elles régissent les performances, le coût et la durabilité de la pile. Les couches actives sont des couches poreuses composées de particules de catalyseur nanostructurées et liées par un polymère conducteur de protons, l'ionomère. Elle est obtenue par séchage, après enduction, d'une encre constituée d'une dispersion des particules de catalyseur et d'ionomère dans un ou plusieurs solvants. Il a été démontré que le fonctionnement de la couche active dépend des paramètres de fabrication, tels que sa composition, le type de solvant de l'encre ou encore le procédé de dépôt et d'assemblage avec les autres composants de la PEMFC. Dans le cadre de cette thèse, la caractérisation structurale de l'ionomère dans la couche active permettra de mieux comprendre les liens se tenant entre sa fabrication et son fonctionnementThe Proton Exchange Membrane Fuel Cell (PEMFC) is an electrochemical converter that produces electricity, heat and water from the oxidation of hydrogen and reduction of oxygen. This efficient and greenhouse gas-free technology is a promising candidate for reducing CO2 emissions, particularly in heavy-duty transportation applications (trucks, buses, etc.). Catalyst layers are the seat of electrochemical reactions and thus the electrodes of the PEMFC. They determine the performance, cost and durability of the fuel cell. Catalyst layers are porous layers composed of nanostructured catalyst particles bound by a proton-conducting polymer, the ionomer. The catalyst layer is obtained by drying, after coating, an ink consisting of a dispersion of catalyst particles and ionomer in one or more solvents. It has been shown that the performance of the catalyst layer depends on manufacturing parameters such as catalyst layer composition, ink solvent type, deposition and assembly process with other PEMFC components. In this work, the structural characterization of the ionomer in the catalyst layer will provide a better understanding of the relationships between its fabrication and operation
8
Zhao, Zuzhen. "Détermination des mécanismes de dégradation d'électrodes modèles de pile à combustible à membrane échangeuse de protons". Phd thesis, Université de Grenoble, 2012. http://tel.archives-ouvertes.fr/tel-00764891.
Testo completoAbstract (sommario):
Ce travail de thèse s'est intéressé aux mécanismes de dégradation de nanoparticules de Pt supportées sur carbone utilisées pour catalyser les réactions électrochimiques dans une pile à combustible à membrane échangeuse de protons (PEMFC) et à leur conséquences d'un point de vue cinétique. Nous avons mis en évidence les différents mécanismes (maturation d'Ostwald 3D, corrosion du support carboné, migration/agrégation des cristallites métalliques) conduisant à une perte de surface active électrochimiquement et avons trouvé des conditions permettent d'isoler chacun de ces mécanismes. En premier lieu, nous avons montré que les nanoparticules de Pt supportées sur carbone ne sont pas immobiles mais agrègent en conditions réactionnelles notamment en présence de molécules réductrices. La vitesse de ce processus varie dans l'ordre CO > CH3OH > H2 et a été reliée à (i) la baisse du travail d'adhésion engendrée par la chimisorption de ces molécules et (ii) la réduction des groupements oxygénés présents sur le support carboné natif.Nous nous sommes également intéressés au mécanisme d'électrooxydation électrochimique du Vulcan XC72, un noir de carbone classiquement utilisé dans les couches catalytiques de PEMFC. Des mesures par spectroscopie Raman ont montré que les domaines désordonnés du Vulcan XC72 (non-graphitiques, hybridation sp3) sont corrodés de façon préférentielle dans des conditions expérimentales proches de celles d'une cathode de PEMFC. Les domaines ordonnés du support carboné (carbone graphitique, hybridation sp2) sont également corrodés, la vitesse de ce processus étant largement inférieure à ce qui est observé sur les domaines désordonnés. En conséquence, les nanoparticules de Pt se détachent ou agglomèrent comme le révèlent des expériences de microscopie électronique en transmission couplées à l'électrochimie. L'ensemble de ces mécanismes de dégradation conduit à un abaissement de la densité du nombre de particules métalliques et augmente la distance entre ces dernières. Dans le chapitre IV, nous montrons que des électrocatalyseurs Pt/Sibunit electrocatalysts possédant (i) un faible chargement massique en Pt, et (ii) de grandes distances inter-particules présentant une faible activité pour la réduction du dioxygène de l'air. Le nombre moyen d'électrons transférés par molécule de dioxygène décroît bien sous la valeur théorique de 4 lorsque l'épaisseur de la couche catalytique ou le chargement massique diminue. Nous avons relié cela à un transport et à une ré-adsorption plus difficiles des intermédiaires réactionnels notamment le péroxyde d'hydrogène. Une diminution du nombre de sites catalytiques peut également engendrer une limitation des cinétiques réactionnelles par l'adsorption de l'oxygène. Au vu de l'ensemble des résultats précédents, nous avons conclu que des cristallites de plus grande taille permettraient d'améliorer la durabilité des matériaux contenus dans les couches catalytiques de PEMFC. Des nano-fils de Pt (NWs) avec une taille moyenne de cristallite de 2,1 ± 0,2 nm ont été synthétisés. Nous avons montré que la morphologie du matériau joue un rôle conséquent à la fois en termes d'activité électrocatalytique et de durabilité : les matériaux Pt NWs/C permettent une réduction de prêt de 170 mV de la surtension d'oxydation d'une monocouche de monoxyde de carbone et possèdent une activité catalytique élevée et stable pour l'électrooxydation du méthanol. Cette dernière a été attribuée à (i) l'augmentation de la masse des cristallites de Pt résultant de l'augmentation en taille (nanoparticules à nano-fils) et (ii) une surface de contact élevée avec le support carboné. Ces matériaux possèdent un potentiel intéressant pour résoudre les problèmes de durabilité rencontrés avec les matériaux 0D utilisés de façon conventionnelle.
9
Dijoux, Étienne. "Contrôle tolérant aux défauts appliqué aux systèmes pile à combustible à membrane échangeuse de protons (pemfc)". Thesis, La Réunion, 2019. http://www.theses.fr/2019LARE0008/document.
Testo completoAbstract (sommario):
La pile à combustible apparaît comme un système performant pour produire de l’électricité « verte » à partir de l’hydrogène dès lors que celui-ci est produit à partir de sources d’énergie renouvelables. Les avantages et la maturité de la technologie à membrane polymère font des PEMFC des candidates prometteuses. Cependant, plusieurs verrous scientifiques et technologiques limitent encore leur utilisation à grande échelle, en particulier leur coût, leur fiabilité et leur durée de vie. L’amélioration de ces caractéristiques passe par la mise en place d’outils de supervision, de détection de défauts et de contrôle des systèmes pile à combustible (PàC). Le travail de recherche est le fruit d’une collaboration entre le FC LAB de l’Université de Bourgogne Franche Comté et le LE2P de l’Université de La Réunion. Ce sujet de thèse s’inscrit dans la continuité des travaux menés au laboratoire FC LAB, portant en particulier sur le diagnostic et le pronostic de systèmes PàC, et des travaux menés au laboratoire LE2P, portant sur le test en ligne d’algorithmes de commande de PEMFC. Parmi les méthodes développées pour déployer la sureté de fonctionnement à un système physique, on retrouve les techniques de tolérance aux défauts, conçues pour maintenir la stabilité du système ainsi que des performances acceptables, même en présence de défauts. Ces techniques se décomposent généralement en trois phases : la détection d’erreurs ou de défaillances, l’identification des défauts à l’origine des problèmes, et l’atténuation. La littérature fait état d’un grand nombre d’outils de diagnostic et d’algorithmes de contrôle, mais l’association du diagnostic et du contrôle reste marginale. L’objectif de ce travail de thèse est donc le test en ligne de différentes stratégies de commande tolérante aux défauts, permettant de maintenir la stabilité du système et des performances acceptables même en présence de défautsFuel cells (FC) are powerful systems for electricity production. They have a good efficiency and do not generate greenhouse gases. This technology involves a lot of scientific fields, which leads to the appearance of strongly inter-dependent parameters. It makes the system particularly hard to control and increase the fault’s occurrence frequency. These two issues underline the necessity to maintain the expected system performance, even in faulty condition. It is a so-called “fault tolerant control” (FTC). The present paper aims to describe the state of the art of FTC applied to the proton exchange membrane fuel cell (PEMFC). The FTC approach is composed of two parts. First, a diagnostic part allows the identification and the isolation of a fault. It requires a good a priori knowledge of all the possible faults in the system. Then, a control part, where an optimal control strategy is needed to find the best operating point or to recover the fault
10
Gloaguen, Frédéric. "Piles à combustible à membrane échangeuse de protons : contribution à l'étude de la cathode à oxygène". Grenoble INPG, 1994. http://www.theses.fr/1994INPG0105.
Testo completoAbstract (sommario):
Le but de ce travail est de minimiser la quantite de platine dans les cathodes a oxygene des piles a combustible envisagees pour les vehicules electriques. La premiere partie de ce memoire comprend une etude bibliographique des piles a combustible a membrane echangeuse de protons (pemfc), ainsi qu'une presentation des principaux resultats concernant la reduction electrochimique de l'oxygene sur platine massif et disperse. Differents modeles, decrivant le fonctionnement des couches actives des electrodes de piles a combustible, sont ensuite etudies. Des applications numeriques au cas de la cathode a oxygene des pemfc permettent de definir les geometries internes des couches actives pour lesquelles l'utilisation du catalyseur est maximale. En utilisant ces modeles, la mise au point d'un protocole de test des proprietes des particules de catalyseur autorise une etude de l'influence de la taille des particules sur l'activite du platine vis a vis de la reduction de l'oxygene. Il est ainsi observe que l'activite massique du platine passe par un maximum pour des tailles de particules comprises entre trois et quatre nanometres. L'interpretation des resultats electrochimiques s'appuie, en partie, sur une experience d'absorption x in situ. Enfin la derniere partie de ce memoire decrit des methodes de preparation de particules de catalyseur par reduction electrochimique de differents complexes du platine
Libri sul tema "Membrane d’échangeuse de protons"
1
Karlsson, Jenny. Functional and structural analysis of the membrane domain of proton-translocating Escherichia coli Transhydrogenase. Göteborg: Department of Chemistry, Biochemistry and Physices, Göteborg University, 2006.
Cerca il testo completo
2
Lester, Packer, a cura di. Biomembranes.: Structure and translocation. Orlando: Academic Press, 1986.
Cerca il testo completo
3
Herring, Andrew M. Fuel cell chemistry and operation. Washington, DC: American Chemical Society, 2010.
Cerca il testo completo
4
1964-, Li Hui, a cura di. Proton exchange membrane fuel cells: Contamination and mitigation strategies. Boca Raton: Taylor & Francis, 2010.
Cerca il testo completo
5
P, Wilkinson David, a cura di. Proton exchange membrane fuel cells: Materials properties and performance. Boca Raton: Taylor & Francis, 2010.
Cerca il testo completo
6
Spiegel, Colleen. PEM fuel cell modeling and simulation using Matlab. Boston: Academic Press/Elsevier, 2008.
Cerca il testo completo
7
Spiegel, Colleen. PEM fuel cell modeling and simulation using Matlab. Boston: Academic Press/Elsevier, 2008.
Cerca il testo completo
8
Spiegel, Colleen. PEM fuel cell modeling and simulation using Matlab. Boston: Academic Press/Elsevier, 2008.
Cerca il testo completo
9
Qi, Zhigang. Proton Exchange Membrane Fuel Cells. Taylor & Francis Group, 2017.
Cerca il testo completo
10
Qi, Zhigang. Proton Exchange Membrane Fuel Cells. Taylor & Francis Group, 2013.
Cerca il testo completoCapitoli di libri sul tema "Membrane d’échangeuse de protons"
1
Alhazov, Artiom. "Number of Protons/Bi-stable Catalysts and Membranes in P Systems. Time-Freeness". In Membrane Computing, 79–95. Berlin, Heidelberg: Springer Berlin Heidelberg, 2006. http://dx.doi.org/10.1007/11603047_6.
Testo completo
2
Casadio, Rita, Giovanni Venturoli e B. Andrea Melandri. "The Determination of the Electrochemical Potential Difference of Protons in Bacterial Chromatophores". In Recent Advances in Biological Membrane Studies, 409–24. Boston, MA: Springer US, 1985. http://dx.doi.org/10.1007/978-1-4684-4979-2_24.
Testo completo
3
Barr, R., e F. L. Crane. "Are Plasmalemma Redox Protons Involved in Growth Control by Plant Cells?" In Plasma Membrane Oxidoreductases in Control of Animal and Plant Growth, 408. Boston, MA: Springer US, 1988. http://dx.doi.org/10.1007/978-1-4684-8029-0_52.
Testo completo
4
Li, Youze, Zhengping Ma e Shaolong Wu. "Studies on the Role of Thylakoid Membrane-Localized Protons in ATP Synthesis". In Current Research in Photosynthesis, 2007–10. Dordrecht: Springer Netherlands, 1990. http://dx.doi.org/10.1007/978-94-009-0511-5_461.
Testo completo
5
Brand, Martin D. "Measurement of mitochondrial protonmotive force". In Bioenergetics, 39–62. Oxford University PressOxford, 1995. http://dx.doi.org/10.1093/oso/9780199634897.003.0003.
Testo completoAbstract (sommario):
Abstract Protonmotive force is the central intermediate in bioenergetics. Mitochondria normally produce it by pumping protons from the mitochondrial matrix across the inner membrane during electron transport. Protonmotive force drives the synthesis of ATP by the ATP synthase as well as several other important bioenergetic reactions such as ion transport, transhydrogenation, and proton leak-mediated heat production.
6
Prebble, John, e Bruce Weber. "The Cytochrome Oxidase Controversy 1977-1986". In Wanderind in the Gardens of the Mind, 222–47. Oxford University PressNew York, NY, 2003. http://dx.doi.org/10.1093/oso/9780195142662.003.0011.
Testo completoAbstract (sommario):
Abstract Mitchell was involved in many controversies. That concerning the cytochronw oxidase> was certainly a major one and throws light on his personality and on his approach to science. lt also provides a window on the nature of scientific debate. ln the late 197us, a major public argtmwnt with a Finnish biochemist developed ove’f an aspe’ct of the chemiosmotic theory. The question under debate, whether or not protons were pumped by the cytochrome oxidase (the terminal enzyme of the respiratory chain that reduces oxygen to water), was related to the more diffuse argument over the number of protons pumped by the respiratory chain, as discussed here earlier. lt was an issue that was to be debated for eight years and in which many of the leaders in the bioenergetics field became involved. For Mitchell personally the underlying basis of the chemiosmotic theory was at stake.The Origins of Mitchell’s View of the Oxidase When Mitchell developed his original theory in the Grey Books of 1966 and 1968, he specifically considered the question of how the passage of electrons down the respiratory chain would move protons across the mitochondrial membrane.
7
Gutman, Menachem, Esther Nachliel e Yossi Tsfadia. "Propagation of Protons at the Water Membrane Interface Microscopic Evaluation of a Macroscopic Process". In Permeability and Stability of Lipid Bilayers, 259–76. CRC Press, 2017. http://dx.doi.org/10.1201/9780203743805-12.
Testo completo
8
Charlene, Pillay, Ramdhani Nishani e Singh Seema. "The Use of Plant Secondary Metabolites in the Treatment of Bacterial Diseases". In Therapeutic Use of Plant Secondary Metabolites, 161–84. BENTHAM SCIENCE PUBLISHERS, 2022. http://dx.doi.org/10.2174/9789815050622122010010.
Testo completoAbstract (sommario):
Plants produce an array of secondary metabolites identified as possible antimicrobialagents that are used across the globe to treat numerous diseases and ailments.These secondary metabolites serve as unique commercial sources of variouspharmaceuticals, food additives and flavouring agents, and possess diverse industrialapplications. Alkaloids, flavonoids, and polyphenols are secondary metabolites shownto attack numerous gram-positive and gram negative bacteria in response to microbialinfections. Secondary plant metabolites have a detrimental effect on microbial cells inseveral ways, such as alteration of the structure and function of the cytoplasmicmembrane as well as DNA/RNA synthesis, interference with intermediary metabolism,interaction with membrane proteins, a disruption in the movement of protons leading toion leakage, enzyme synthesis inhibition, the clotting of cytoplasmic components andinterference in typical cell communication. This ultimately results in cell death. Thefocus of this chapter is to provide an overview of the function and benefits of plantsecondary metabolites as therapeutic agents to combat pathogenic bacterial infections.
9
Choubey, Jyotsna, Jyoti Kant Choudhari, J. Anandkumar, Mukesh Kumar Verma, Tanushree Chaterjee e Biju Prava Sahariah. "Cell Biology, Biochemistry and Metabolism of Unique Anammox Bacteria". In Ammonia Oxidizing Bacteria, 147–57. Royal Society of Chemistry, 2023. http://dx.doi.org/10.1039/bk9781837671960-00147.
Testo completoAbstract (sommario):
Anaerobic ammonium oxidation (anammox) bacteria oxidize ammonium in the absence of oxygen with NO2 as the oxidant instead of oxygen and form dinitrogen (N2) as the end product. Anammox bacteria belong to the phylum Planctomycetes. Anammox bacteria are characterized by a compartmentalized cell architecture featuring a central cell compartment, the “anammoxosome”. This organelle is surrounded by ladderane lipids, which make the organelle nearly impermeable to hydrazine and protons. Anammox bacteria show similarities to both Archaea and Eukarya, making them extremely interesting from a cell biological perspective. Anammox metabolism takes place in a special and unique cell organelle, the anammoxosome. Here, energy released in the anammox reaction is used to generate proton-motive force that drives ATP synthesis. This respiratory process is supported by novel membrane-bound protein complexes. On a global scale, anammox bacteria significantly contribute to the removal of fixed nitrogen from the environment and the process is finding rapidly increasing interest in wastewater treatment. This chapter highlights the current knowledge on the cell biology, biochemistry and metabolism of this unique group of bacteria.
10
Dalton, David R. "Harvesting the Light". In The Chemistry of Wine. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780190687199.003.0018.
Testo completoAbstract (sommario):
Products of reactions are separated from reactants by a barrier or barriers. if this were not so we could not have any reactants—everything would already be products! In order for the grapevine to grow beyond the materials provided in the seed, the rootstock, or the cutting, it is necessary for the reactants obtained from the environment (i.e., nutrients in the soil and air) to be converted to plant material. The energy for this conversion comes from the sun, and it is the chloroplasts that take the light and, using the aforementioned materials, convert it to useful energy in the plant. So, overall, for processes to occur within the plant, a high energy species must be formed and then used. Subsequent regeneration of the high energy species can use more sunlight. The currency of energy is adenosine triphosphate (ATP). When it is used, it is converted to adenosine diphosphate (ADP) and inorganic phosphate (Pi), and in that conversion (or those conversions as more than one can be used to accomplish the same end) the barrier between reactant and product can be overcome (Figure 10.1). Additionally, for moving electrons and protons around where simple solvation (the use of—and interactions with—solvents) will not work, a cofactor (a “factor” that needs to be present in addition to an enzyme to enable the catalyzed reaction to occur) is often needed. These movements of electrons and protons are simply oxidations and reductions (see Appendix 1), and it is common to find oxidation and reduction being effected by using, as cofactors, either the oxidized or reduced forms of the phosphate ester of nicotinamide adenine dinucleotide (NADP+) to/ from (NADPH) and/ or the related conversion of the oxidized/ reduced forms of flavin adenine dinucleotide (FAD)/ (FADH2) (Figure 10.2). A cartoon representation of the chloroplast wall, with the stroma (the colorless fluid filling the chloroplast through which materials move) shown on the top and the lumen of the thylakoid body (where the light- dependent photochemistry occurs) on the bottom is provided in Figure 10.3. The working agents in the membrane are shown.
Atti di convegni sul tema "Membrane d’échangeuse de protons"
1
Cheng, Chin-Hsien, Shu-Feng Lee e Che-Wun Hong. "Molecular Dynamics of Proton Exchange Inside a Nafion® Membrane". In ASME 2006 4th International Conference on Fuel Cell Science, Engineering and Technology. ASMEDC, 2006. http://dx.doi.org/10.1115/fuelcell2006-97135.
Testo completoAbstract (sommario):
The proton transfer mechanism is the fundamental principle of how the proton exchange membrane fuel cell (PEMFC) works. This paper develops a molecular dynamics technique to simulate the transfer mechanism of the hydrogen protons inside a Nafion 117 membrane. The realistic polymer structure of the Nafion is extremely huge and very complex, it is simplified to be a repeated structure with part of the major carbon-fluoride backbone and a side chain with radicals of SO3− in this paper. Water molecules were assigned to distribute between side chains randomly. The simulation package of DLPOLY was employed as the platform. Simulation results show that the water molecules will cluster together due to the polarization characteristics, and the clusters are attracted by the side chain of the membrane electrolyte. Hydrogen protons are then transferred from one side chain to another through the water clusters. The migration process of the hydrogen protons within the membrane is a function of the water uptakes and many other factors. They are investigated to further improve the ionic conduction of the fuel cell membrane.
2
Eaton, Brandon, Michael R. von Spakovsky, Michael W. Ellis, Douglas J. Nelson, Benoit Olsommer e Nathan Siegel. "One-Dimensional, Transient Model of Heat, Mass, and Charge Transfer in a Proton Exchange Membrane". In ASME 2001 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2001. http://dx.doi.org/10.1115/imece2001/aes-23652.
Testo completoAbstract (sommario):
Abstract A transient, one-dimensional, model of the membrane of a proton exchange membrane fuel cell is presented. The role of the membrane is to transport protons from the anode to cathode of the fuel cell while preventing the transport of other reactants. The membrane is modeled assuming mono-phase, multi-species flow. For water transport, the principle driving forces modeled are a convective force, an osmotic force (i.e. diffusion), and an electric force. The first of these results from a pressure gradient, the second from a concentration gradient, and the third from the migration of protons from anode to cathode and their effect (drag) on the dipole water molecules. Equations are developed for the conservation of protons and water, the conservation of thermal energy, and the variation of proton potential within the membrane. The model is solved using a fully implicit finite difference approach. Results showing the effects of current density, pressure gradients, water and heat fluxes, and fuel cell start-up on water concentration, temperature, and proton potential across the membrane are presented.
3
Chiu, Chuang-Pin, Peng-Yu Chen e Che-Wun Hong. "Atomistic Analysis of Proton Diffusivity at Enzymatic Biofuel Cell Anode". In ASME 2006 4th International Conference on Fuel Cell Science, Engineering and Technology. ASMEDC, 2006. http://dx.doi.org/10.1115/fuelcell2006-97136.
Testo completoAbstract (sommario):
This paper investigates the proton diffusion phenomenon between the anode catalyst and the electrode in an enzymatic bio-fuel cell. The bio-fuel cell uses enzymatic organism as the catalyst instead of the traditional noble metal, like platinum. The fuel is normally the glucose solution. The fuel cell is membrane-less and produces electricity from the reaction taken place in the organism. When the biochemical reaction occurs, the protons and electrons are released in the solution. The electrons are collected by the electrode plate and are transported to the cathode through an external circuit, while the protons migrate to the cathode by the way of diffusion. Unfortunately, protons are easy to dissipate in the solution because the enzyme is immersed in the neutral electrolyte. It is an important issue of how to collect the protons effectively. In order to investigate the diffusion process of the protons, a molecular dynamics simulation technique was developed. The simulation results track the transfer motion of the protons near the anode. The diffusivity was evaluated from the trajectory. The research concludes that the higher the glucose concentration, the better the proton diffusivity. The enzyme promotes the electrochemical reaction; however, it also plays an obstacle in the proton diffusion path.
4
Gai, Feng, Kenton C. Hasson e Philip A. Anfinrud. "Ultrafast Photoisomerization of Retinal in Bacteriorhodopsin: A New Twist". In International Conference on Ultrafast Phenomena. Washington, D.C.: Optica Publishing Group, 1996. http://dx.doi.org/10.1364/up.1996.fc.5.
Testo completoAbstract (sommario):
Bacteriorhodopsin (BR) is a membrane protein which converts light energy to chemical energy by pumping protons unidirectionally across the membrane. The driving force for pumping protons is derived from the photoisomerization of all-trans retinal to 13-cis retinal, the quantum yield of which is reported to be approximately 0.61. The quantum yield appears to be independent of temperature and is minimally affected by mutations to numerous neighboring residues in the protein. Previous studies have suggested that photoexcited BR relaxes in 0.5 ps to J which in turn relaxes in 3 ps to K2. The long-lived intermediate K has been identified as the 13-cis isomer of retinal3. The relative constancy of the quantum yield for the formation of K is not well understood, nor are the differences between J and K. To investigate the primary photoprocesses of BR as well as the role of the protein in mediating the photoisomerization of retinal, we measured time-resolved absorbance spectra over a broad spectral range with high sensitivity.
5
Cheng, Chin-Hsien. "Nano-Scale Transport Phenomena and Thermal Effect of the PEMFC Electrolyte". In ASME 2008 First International Conference on Micro/Nanoscale Heat Transfer. ASMEDC, 2008. http://dx.doi.org/10.1115/mnht2008-52323.
Testo completoAbstract (sommario):
This paper employed molecular dynamics (MD) simulation to investigate the transport phenomena and thermal effect at nano-scale inside fuel cell electrolyte. The material of the electrolyte was chosen to be Nafion® which is the most commonly used material for proton exchange membrane fuel cell (PEMFC). The transport of protons inside the electrolyte is one of the major issues that influencing the fuel cell performance. The structure of the Nafion® includes carbon-fluorine back bones and side chains (with SO3− attached at the end). Simulation results show that the transport of protons was confined to some specific regions. These specific regions (hydrophilic phase region) consist of water molecules, protons and sulfonated acid groups. Different hydration levels (3, 61.25, 9 and 15.375 H2O/SO3−) was also studied to test the sensitivity of the electrolyte water content on proton conduction. Higher water content shows greater proton mobility due to the larger water cluster size and more water clusters. The influence of the temperatures (333K, 343K and 353K) on proton mobility was due to different sizes of hydrophilic phase regions. Diffusion coefficients at various operation conditions were also evaluated and showed satisfactory agreement with the published experimental data.
6
Drochioiu, Gabi. "THE ROLE OF BACTERIORHODOPSIN IN LIGHT HARVESTING AND ATP PRODUCTION BY HALOBACTERIUM SALINARUM CELLS". In 22nd SGEM International Multidisciplinary Scientific GeoConference 2022. STEF92 Technology, 2022. http://dx.doi.org/10.5593/sgem2022/6.1/s25.17.
Testo completoAbstract (sommario):
Halobacterium salinarum is an extremely halophilic marine Gram-negative obligate aerobic archaeon. Despite its name, this is not a bacterium, but rather a member of the domain Archaea, which lives in hypersaline lakes. Bacteriorhodopsin (BRh) is the red retinal-containing protein found in the cell membranes of H. salinarum and is considered a light-activated proton pump that transports protons across the plasma membrane. Bacteriorhodopsin photointermediates have been defined in kinetic and spectroscopic terms as BR568, K590, L550, M412, N560, and O640. We have previously shown, using the Forster cycle for BRh that its acidity increases greatly on illumination. Therefore, protons released upon illumination of the L550 intermediate with 412 nm light may not play an essential role in ATP production. Instead, the light-induced excitation energy, which represents the energy difference between the L550 and M412 states, can be used to extract an ATP molecule attached to ATP synthase. Thus, we have shown that this amount of energy corresponds to a near-infrared vibration, which is sufficient for ATP production and provides the most feasible molecular mechanism for this phenomenon. Here, we provide new evidence that protons are released due to BRh excitation, unrelated to ATP synthesis, being only a secondary phenomenon. In addition, once released from H. salinarum cells, protons should return back into the cells via ATP-synthase molecules to produce ATP. This is not possible at pH > 7.0, such as pH 9.5. However, the stability of M intermediates and ATP formation appear to be increased at higher pH values. Indeed, a spectral shift of 138 nm may be associated with an energy amount of about 17 kcal mol-1, which is enough energy to release a mole of ATP from ATP-synthase. In general, light excitation of fluorescent molecules is a phenomenon that induces a strong increase in their acidity. Recent data suggest that the chemiosmotic hypothesis put forward by Peter Mitchell to explain ATP formation in living cells is not correct, at least in terms of explaining light-induced ATP production in H. salinarum cells.
7
Xiao, Yu, Jinliang Yuan e Bengt Sunde´n. "On Modeling Development of Microscopic Spatial Structure for the Catalyst Layer in a Proton Exchange Membrane Fuel Cell". In ASME 2011 9th International Conference on Fuel Cell Science, Engineering and Technology collocated with ASME 2011 5th International Conference on Energy Sustainability. ASMEDC, 2011. http://dx.doi.org/10.1115/fuelcell2011-54882.
Testo completoAbstract (sommario):
The typical catalyst layers (CLs) in proton exchange membrane fuel cells (PEMFCs) are fabricated as random heterogeneous composites to meet the multifunctional requirements of transport phenomena and electrochemical activity. The employment of Pt nano-particles, carbonaceous substrates and Nafion ionomers in CLs allows effective diffusion of hydrogen and oxygen, transport and phase change of water, migration and diffusion of protons, migration of electrons to and from the catalytic sites, which is accompanied by the oxidation of hydrogen in anodes and the generation of water and heat in cathodes. Based on the coarse-grained (CG) molecular dynamics method, a systematic technique is developed to provide insight into the self-organization phenomena and the microscopic spatial structure of the CLs. The formation of a CL is simulated by considering the interactions of the Pt clusters, carbon slabs, Nafion ionomers, hydronium ions and water. Meanwhile, the morphologies of Pt clusters are presented and compared with three cases. Moreover, the pair correlation functions (PCFs) are employed to predict the distributions and hydrophilic properties of the components. Finally, the TPB features are shown at the nano-scale level, which provides deeper view to understand the Pt utilization in the CLs.
8
Vang, Jakob Rabjerg, So̸ren Juhl Andreasen e So̸ren Knudsen Kær. "A Transient Fuel Cell Model to Simulate HTPEM Fuel Cell Impedance Spectra". In ASME 2011 9th International Conference on Fuel Cell Science, Engineering and Technology collocated with ASME 2011 5th International Conference on Energy Sustainability. ASMEDC, 2011. http://dx.doi.org/10.1115/fuelcell2011-54880.
Testo completoAbstract (sommario):
This paper presents a spatially resolved transient fuel cell model applied to the simulation of high temperature PEM fuel cell impedance spectra. The model is developed using a 2D finite volume method approach. The model is resolved along the channel and across the membrane. The model considers diffusion of cathode gas species in gas diffusion layers and catalyst layer, transport of protons in the membrane and the catalyst layers, and double layer capacitive effects in the catalyst layers. The model has been fitted simultaneously to a polarisation curve and to an impedance spectrum recorded in the laboratory. A simultaneous fit to both curves is not achieved. In order to investigate the effects of the fitting parameters on the simulation results, a parameter variation study is carried out. It is concluded that some of the fitting parameters assume values which are not realistic. In order to remedy this, phenomena neglected in this version of the model must be incorporated in future versions.
9
Daino, Michael M., e Satish G. Kandlikar. "Evaluation of Imaging Techniques Applied to Water Management Research in PEMFCs". In ASME 2009 7th International Conference on Nanochannels, Microchannels, and Minichannels. ASMEDC, 2009. http://dx.doi.org/10.1115/icnmm2009-82031.
Testo completoAbstract (sommario):
Water management in proton exchange membrane fuel cells (PEMFCs) is critical in efficient operation of fuel cells during normal operation as well as purge and start-up conditions. Insufficient membrane hydration impedes the flow of protons and an overabundance of water obstructs the flow of reactants in the gas diffusion layer (GDL) and in gas distribution channels. These two extremes of water content in PEMFCs significantly reduce performance and efficiency, causing material degradation and potential failure. Visualization and quantitative measurement of water content in PEMFCs lead to greater comprehension of water distribution and transport processes. A wide variety of imaging techniques have been employed in literature to reveal water distribution and transport processes on both macroscale and microscale. The presented techniques utilize visible, infrared, X-rays, fluorescence microscopy, nuclear magnetic resonance (NMR), and neutron radiography to visualize water, measure temperature distributions, and quantify water content. Each imaging technique has intrinsic advantages, disadvantages, and limitations for water detection and will be discussed. A critical evaluation of these techniques and their suitability for visualization of specific components of PEMFC are also discussed.
10
Hashizume, Hiroki, Kentaro Doi e Satoyuki Kawano. "Improvement of Proton Conduction in PEFC by Applying External Perturbations". In ASME-JSME-KSME 2011 Joint Fluids Engineering Conference. ASMEDC, 2011. http://dx.doi.org/10.1115/ajk2011-36034.
Testo completoAbstract (sommario):
In fuel cell technologies, there are some problems which should be overcome rapidly. For example, it is known that voltage losses in polymer electrolyte fuel cells are serious problems. However, drastic solutions have not been found out yet. In the present study, we experimentally try to improve the energy conversion efficiency, focusing on ion currents in electrode membrane assemblies (MEAs). Additional Ag electrodes are fabricated on an MEA and their effects on proton flows are investigated. Consequently, it is found that electric voltage losses can be suppressed by electric or ion currents parallel to the proton flow. This result suggests that the external perturbations can be effective to protons and oxygen molecules on their reactions and on the power generation efficiency.
Rapporti di organizzazioni sul tema "Membrane d’échangeuse de protons"
1
Nelson, Nathan, e Randy Schekman. Functional Biogenesis of V-ATPase in the Vacuolar System of Plants and Fungi. United States Department of Agriculture, settembre 1996. http://dx.doi.org/10.32747/1996.7574342.bard.
Testo completoAbstract (sommario):
The vacuolar H+-ATPase (V-ATPase) is one of the most fundamental enzymes in nature. It pumps protons into the vacuolar system of eukaryotic cells and provides the energy for numerous transport systems. Through our BARD grant we discovered a novel family of membrane chaperones that modulate the amount of membrane proteins. We also elucidated the mechanism by which assembly factors guide the membrane sector of V-ATPase from the endoplasmic reticulum to the Golgi apparatus. The major goal of the research was to understand the mechanism of action and biogenesis of V-ATPase in higher plants and fungi. The fundamental question of the extent of acidification in organelles of the vacuolar system was addressed by studying the V-ATPase of lemon fruit, constructing lemon cDNAs libraries and study their expression in mutant yeast cells. The biogenesis of the enzyme and its function in the Golgi apparatus was studied in yeast utilizing a gallery of secretory mutants available in our laboratories. One of the goals of this project is to determine biochemically and genetically how V-ATPase is assembled into the different membranes of a wide variety of organelles and what is the mechanism of its action.The results of this project advanced out knowledge along these lines.