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

Elaboration et etude structurale de membranes ionmeres perfluorees obtenues a partir de solutions

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Inside the structure of a nanocomposite electrolyte membrane: how hybrid particles get along with the polymer matrix

International audienceHybrid materials remain the target for a fruitful range of investigations, especially for energy devices. A number of hybrid electrolyte membranes consisting of inorganic and organic phases were then synthesized. Mechanical, solvent uptake and ionic transport properties were studied with the key point being the characteristic length scale of the interaction between the phases. A group of nanocomposite membranes made of polystyrenesulfonic acid-grafted silica particles embedded in a Poly(Vinylidene Fluoride-co-HexaFluoroPropene) (PVdF-HFP) matrix was studied by combining neutron and X-ray scatterings on the nanometer to angstrom scale. This approach allows for the variation in the morphology and structure as a function of particle loading to be described. These studies showed that the particles aggregate with increasing particle loading and these aggregates swell, creating a physical interaction with the polymer matrix. Particle loadings lower than 30 wt% induce a slight strain between both of the subphases, namely the polymer matrix and the particles. This strain is decreased with particle loading between 20 and 30 wt% conjointly with the beginning of proton conduction. Then the percolation of the aggregates is the beginning of a significant increase of the conduction without any strain. This new insight can give information on the variation in other important intrinsic properties

Heterogeneous Nanostructural Aging of Fuel Cell Ionomer Revealed by Operando SAXS

International audienceProton exchange membrane fuel cells (PEMFCs) represent one of the most interesting technologies for powering vehicles and small portable electronic devices in an eco-friendly way. Large scale implementation of PEMFCs requires to tailor novel resilient economically viable materials with prolongated lifetimes. One key issue is the durability of the ionomer membrane, which is responsible for the conduction of protons from anode to cathode. Here we report on the impact of aging on the membrane structure by means of operando SAXS. By analyzing the most prominent features of the in-situ aged and pristine spectra at different relevant positions in the fuel cell, we could establish that structural aging is highly heterogeneous and strongly dependent on the local conditions. The increase in current density produces a decrease in ionic nanodomain sizes in aged ionomer due to continuous membrane drying, as in pristine materials. However, long-term operation most dramatically affects the polymer organization into bundles, in particular at the air inlet and in the middle of the cell. Variations of the low-angle intensity of more than an order of magnitude are ascribed to significant increase in the area of interfacial regions, potentially impacting the diffusion within grain boundaries. With this study, we demonstrate that operando SAXS provides unique insights into ionomer structural aging in dependence of the local hydration and helps to identify the relevant scale for physical degradation. This information is needed for optimizing fuel cells operating strategies and improving the durability of membranes

Combined Operando High Resolution SANS and Neutron Imaging Reveals in-Situ Local Water Distribution in an Operating Fuel Cell

International audienc

ELENA Commissioning

The Extra Low ENergy Antiproton storage ring (ELENA) is an upgrade project at the CERN AD (Antiproton Decelerator). ELENA will further decelerate the 5.3 MeV antiprotons coming from the AD down to 100 keV. ELENA features electron cooling for emittance control during deceleration thus preserving the beam intensity and allowing to extract bright bunches towards the experiments. The lower energy will allow for increasing the antiproton trapping efficiency up to two orders of magnitude, which is typically less than 1% with the present beam from AD. The ring was completed with the installation of the electron cooler at the beginning of 2018. Decelerated beams with characteristics close to the design values were obtained before the start of CERN Long Shutdown 2 (LS2). During LS2 electrostatic transfer lines from the ELENA ring to the experimental zones will be installed, replacing the magnetic transfer lines from the AD ring. The latest results of commissioning with H⁻ and antiprotons and the first observation of electron cooling in ELENA will be presented, together with an overview of the project and status and plans for LS2 and beyond