Résumé:Ici est présentée une étude expérimentale de la transition solide-fluide dans un gel du type "fluide a seuil" (Carbopol 940)

No abstract

Photo-active layers from non-stabilized P3HT:ICBA nanoparticles enable the fabrication of inverted organic solar cells from eco-friendly, alcoholic dispersions. Exhibiting power conversion efficiencies (PCEs) ≈4%, the devices are competitive to state-of-the-art P3HT:ICBA solar cells from chlorinated solvents. Upon thermal annealing, the short circuit current density and consequently the PCE of the inverted solar cells improve radically due to a more intimate contact of the nanoparticles and hence an enhanced charge carrier extraction.

We visualize the flow induced by an isolated non-Brownian spherical particle settling in a shear thinning yield stress fluid using particle image velocimetry. With ReϽ 1, we show a breaking of the fore-aft symmetry and relate this to the rheological properties of the fluid. We find that the shape of the yield surface approximates that of an ovoid spheroid with its major axis approximately five times greater than the radius of the particle. The disagreement of our experimental findings with previous numerical simulations is discussed.

Image analysis and numerical simulation algorithms are introduced to analyze the micro‐structure, transport, and electrochemical performance of thin, low platinum loading inkjet printed electrodes. A local thresholding algorithm is used to extract the catalyst layer pore morphology from focused ion beam scanning electron microscopy (FIB‐SEM) images. n‐point correlation functions, such as auto‐correlation, chord length, and pore‐size distribution are computed to interpret the micro‐structure variations between different images of the same catalyst layer. Pore size distributions are in agreement with experimental results. The catalyst layer exhibits anisotropy in the through‐plane direction, and artificial anisotropy in the FIB direction due to low slicing resolution. Microscale numerical mass transport simulations show that transport predictions are affected by image resolution and that a minimum domain size of 200 nm is needed to estimate transport properties. A micro‐scale electrochemical model that includes a description of the ionomer film resistance and a multi‐step electrochemical reaction model for the oxygen reduction reaction is also presented. Results show that the interfacial mass transport resistance in the ionomer film has the largest effect on the electrochemical performance.

No abstract

Membrane electrode assemblies were degraded by voltage cycling in hydrogen/air atmosphere. The impact of degradation on fuel cell performance was measured by various electrochemical characterization techniques. Loss of electrochemically active surface area was correlated to kinetic voltage losses at low current density as well as losses at high current density due to oxygen transport limitations. It was found that the oxygen transport resistance scales proportionally to the inverse of normalized platinum surface area. The change in the catalyst layer structural properties due to voltage cycling was visualized by electron microscopy. A new method of calculating changes in platinum loading of degraded samples by transmission electron microscopy is presented and shows redistribution of platinum in the catalyst layer due to platinum dissolution.

No abstract