Morphology of supported polymer electrolyte ultra-thin films: a numerical study

Morphology of polymer electrolytes membranes (PEM), e.g., Nafion, inside PEM fuel cell catalyst layers has significant impact on the electrochemical activity and transport phenomena that determine cell performance. In those regions, Nafion can be found as an ultra-thin film, coating the catalyst and the catalyst support surfaces. The impact of the hydrophilic/hydrophobic character of these surfaces on the structural formation of the films has not been sufficiently explored yet. Here, we report about Molecular Dynamics simulation investigation of the substrate effects on the ionomer ultra-thin film morphology at different hydration levels. We use a mean-field-like model we introduced in previous publications for the interaction of the hydrated Nafion ionomer with a substrate, characterized by a tunable degree of hydrophilicity. We show that the affinity of the substrate with water plays a crucial role in the molecular rearrangement of the ionomer film, resulting in completely different morphologies. Detailed structural description in different regions of the film shows evidences of strongly heterogeneous behavior. A qualitative discussion of the implications of our observations on the PEMFC catalyst layer performance is finally proposed

Nanofiltration of hormone mimicking trace organic contaminants

The removal mechanisms of three hormone mimicking organic compounds by nanofiltration (NF) membranes have been examined. Two NF membranes having different pore size were used in laboratory-scale nanofiltration experiments with feed solutions spiked with a hormone mimicking compound ¾ nonylphenol, tert-butyl phenol, or bisphenol A. Retention of the compounds was determined at various solution chemistries, namely aqueous solution pH, ionic strength, and presence of natural organic matter. The nanofiltration behavior of the selected hormone mimicking compounds appears similar to that of natural hormones as reported in our previous work. While the solution pH can dramatically influence the retention of hormone mimicking compounds by a loose NF membrane, ionic strength does not affect the nanofiltration of such contaminants. However, in the presence of natural organic matter in the feed solution, ionic strength appears to play a significant role in solute-solute and solute-membrane interactions, resulting in increased retention due to partitioning of the hormone mimicking compounds onto organic matter at a higher ionic strength

Microfluidic NF/RO separation: Cell design, performance and application

Microfluidics have seen a steady expansion of the operation toolbox over the last decade, which includes membrane separations as well. However, the latter are mainly limited to low-pressure operations such as dialysis, MF and UF with only very few reports focusing on high-pressure processes such as NF and RO. In this report a simple high-pressure microfluidic cell suitable for accommodating NF and RO membranes is described and critical design points are discussed. It is shown, both theoretically, using computational fluid dynamics (CFD) and Lévêque correlation, and experimentally, that a smaller height of the feed channel is beneficial for minimizing concentration polarization. Minimization of overall pressure losses, hydraulic and osmotic, indicates an optimal channel height of about 40–50 μm. The NF/RO microcell was tested as a concentrator for solution of a model peptide. The solution was successfully concentrated, however, a significant loss of peptide was observed, presumably, due to adsorption on the membrane or cell walls. This problem will need to be addressed in future studies of NF/RO microcells, however, this work demonstrates the potential and feasibility of implementing RO and NF operations in microfluidic technolog

Une cause rare d’épanchement pleural

International audienc

Usefulness of multidetector-row computerized tomographic angiography for the surgical planning in stereoelectroencephalography

International audienc