In recent years, an increasing pursuit of product appearance, so the surface appearance of the product are the main arc, but if we can develop the flexible fuel cells, fuel cells will be able to scratch-type adhesive on the product curved surface, not only for product supply and portable, low pollution have great potential for portable fuel cells. Performance of the experiment found that the decision lies in the amount of carbon fiber bundles, softness and spring pressure on the uniformity imposed by such factors. The experiment that bending radius of curvature of 45.5cm, the battery around the X, Y, XY axis deflection performance and the performance is not the same, and the radius of curvature around the X-axis deflection narrow, performance is not reduced, around the XY axis deflection narrow the radius of curvature, the performance has not decreased significantly, but the radius of curvature around the Y-axis deflection reduced, performance has slightly dropped, from IV Curve that the radius of curvature smaller fiber bundles and electrode contact resistance also increases, but this performance decline in the acceptable range. This will be a torsion-type fuel cell, can be the radius of curvature 45.5 ~ 10.58cm or less within the flexural performance, this battery has the potential of portable fuel cells, advantages of low pollution, high efficiency and easy to carry.

This paper presents analytical and experimental studies on optimization of the gas delivery and current collection system in a proton exchange membrane (PEM) fuel cell for the objective of reducing ohmic loss, thereby achieving higher power density. Specifically, the dimensions of current collection ribs as well as the rib distribution were optimized to get a maximized power density in a fuel cell. In the modeling process, the power output from a fixed area of membrane is calculated through analysis of an electrical circuit simulating the current from electrochemical reaction flowing to the current collectors. Current collectors of two-dimensional ribs and three-dimensional pillars were considered. Analyses found that three-dimensional pillars allow higher power density in a PEM fuel cell. Considering the mass transfer enhancement effect, three-dimensional pillars as current collectors in gas flow field may be a good choice if the fuel cell operates at low current density and there is no liquid water blocking the flow channels. The analyses did not consider the existence of liquid water, meaning the current density is not very high. The study concluded that decreasing the size of both the current collector and its control area yields a significant benefit to a higher power density. A preliminary experimental test in a PEM fuel cell has verified the conclusion of the analytical work.

The reversible electrochemistry and the superior gravimetric and volumetric energy storage capacities of lithium ion batteries (LIBs) have propelled them as the dominant power source for a range of portable electronic devices. Thin film LIBs are a class of LIBs that have been extensively used for powering Microelectromechanical systems devices, Radio-frequency Identification tags, biomedical sensors and several other low power electronic systems. Thin film electrodes and electrolytes are characteristic of short lithium ion diffusion paths and hence show fast charge/discharge rates. But the thin film battery technology has the major drawback of possessing low energy per footprint area. The three dimensional design for thin film LIBs has been proposed to improve electrode mass loading per footprint area thereby improving the energy delivered by the device. Hence there is interest in assembling the entire battery (current collectors, anode, electrolyte, and cathode) in a three dimensional (3D) nanostructured architecture. This thesis deals with the development and assembly of nanostructured three dimensional designs for Li ion battery components. Several template-based techniques have been used to fabricate nanostructured materials which serve as building blocks for the 3D energy storage devices. Firstly we have addressed the challenging task of fabricating conformal nanostructured polymer electrolytes around nanowire electrode material. The polymer coatings helped in controlling the secondary electrolyte interphase formation and hence in the improvement of cycling characteristics of the nanowire electrode material. We have also fabricated 3D current collectors with both ordered and disordered pore structure. Electrodes coated on 3D nanostructured current collectors showed improved rate capability and energy per footprint area. Finally, we have used a bottom up approach to assemble all essential components (anode, electrolyte, and cathode) of an electrochemical energy storage device onto a single nanowire, and have tested a parallel array of such nanowire devices for its electrochemical performance, hence demonstrating the ultimate miniaturization possible for energy storage devices.

No description available.

Répondre aux besoins énergétiques croissants de nos sociétés et limiter leur impact sur l’environnement est un enjeu actuel majeur. De nouvelles technologies alternatives comptent tirer profit de sources d’énergie négligées. Le potentiel énergétique des eaux usées peut être exploité par de nouvelles technologies telles que les piles à combustible microbiennes (PACM). Ces piles, pouvant produire de l’énergie électrique à partir d’eaux usées, montrent une diminution de leur rendement énergétique lorsque leur taille augmente, ce qui ne permet pas encore leur application industrielle. Ces travaux de thèse visent à identifier certains verrous de ce changement d’échelle et à proposer de nouvelles directions pour leur optimisation. Une première partie s’est intéressée à l’influence des collecteurs de courant anodiques sur les performances électriques et sur le développement du biofilm électro-actif. Nous avons émis l’hypothèse qu’à grande échelle, les collecteurs de courant peuvent être un élément limitant à la production d’électricité. Pour vérifier cette hypothèse, quatre PACM avec une anode de 490 cm² connectée de différentes manières ont été étudiées. L’augmentation du nombre de collecteurs a permis une hausse de la puissance produite par les PACM. La disposition des collecteurs affecte la répartition du potentiel sur la surface d’anode et peut engendrer dans certains cas, des gradients de potentiel qui influencent la structure microbiologique du biofilm, en particulier Geobacter. Par ailleurs, des mesures d’impédance ont montré que multiplier les collecteurs augmente la capacité de double couche de l’anode et engendre un courant capacitif dont l’importance pour les performances de fonctionnement en cycles de charge/décharge est non négligeable. La suite du travail s’est attachée à prendre en compte différents aspects physiques, notamment l’aspect hydrodynamique, afin de modéliser leur fonctionnement. Pour cela, trois PACM de volumes différents ont été mises en œuvre et testées à différents débits. Les données de configuration, d’opération et de performances de ces piles ont permis de construire des modèles statistiques de régression linéaire multiple prédisant la valeur de puissance maximale. Ces deux modèles ont montré que la puissance maximale produite était principalement corrélée à la vitesse de l’électrolyte circulant dans la pile et à la contrainte de cisaillement appliquée à l’anode par le mouvement du fluide. Ces deux parties ont également montré que l’abondance dans le biofilm de Geobacter, une bactérie électro-active très répandue dans les PACM, n’était pas corrélée avec la puissance maximale. Tout en étant très abondante, son seul nombre n’explique donc pas entièrement les performances électriques d’une PACM. / Facing increasing energy needs and limiting their impact on the environment are current and major issues for society. Renewable energy development is needed and new alternative technologies could benefit from exploiting neglected energy sources, such as microbial fuel cells (MFC), for energy production. MFCs can be operated with wastewater and produce a reasonable quantity of energy at the small laboratory-scale. Unfortunately, when their size is increased, their efficiency dramatically decreases, which prevents their industrial use. This thesis aims at identifying some obstacles to scale-up of MFC and proposing new directions for its optimization. The first part of the study was focused on the influence of anodic current collectors on electrical performance and on electroactive biofilm development. Our hypothesis was that they could be a limiting factor for electricity production at large scales. To test this hypothesis, four MFCs were operated with a 490 cm² anode connected to the external circuit in a different ways. Increasing the number of collectors improved the power. Collector’s layout influenced electrical potential on the anode surface and created an electrical potential gradient on the anode and this gradient shaped the microbiological structure of the biofilm. This effect especially concerns Geobacter, whose clade G. metallireducens is favored at strongly negative potentials. In addition, impedance measurements showed that multiplying collectors increased the double layer capacitance and, thus, generated a capacitive current that was important for MFC functioning in cycles of charge/discharge and that would improve its performance. Then, MFCs were considered as bioreactors and their different aspects, notably hydrodynamics, were taken into account to model their power output. Three MFCs of different volumes were operated under continuous-flow conditions and tested at four different flow rates. Configuration, operation and performance data were used to build two multiple linear regression statistical models: the first with variables selection through LASSO, the second with dimensionless numbers created with the Vaschy-Buckingham theorem. These two data-driven models showed that the maximal power was mostly correlated to electrolyte transfer rates inside MFC chamber and to shear stress at the anode generated by fluid movement. These two major experimental projects also showed that the abundance of Geobacter, an electroactive bacteria, inside the biofilm was widespread in MFCs, but it was not correlated to maximal power. Despite its large abundance, its quantity alone does not entirely explain the performance of a MFC. In order to succeed at MFC scale-up, fundamental research on electroactive biofilms, process engineering and modeling need to be associated and generalized as empirical results and their explanation.

No description available.