Stéphane Chevalier

Calibrating the X-ray attenuation of liquid water and correcting sample movement artefacts during in operando synchrotron X-ray radiographic imaging of polymer electrolyte membrane fuel cells

Synchrotron X-ray radiography, due to its high temporal and spatial resolutions, provides a valuable means for understanding the in operando water transport behaviour in polymer electrolyte membrane fuel cells. The purpose of this study is to address the specific artefact of imaging sample movement, which poses a significant challenge to synchrotron-based imaging for fuel cell diagnostics. Specifically, the impact of the micrometer-scale movement of the sample was determined, and a correction methodology was developed. At a photon energy level of 20 keV, a maximum movement of 7.5 µm resulted in a false water thickness of 0.93 cm (9% higher than the maximum amount of water that the experimental apparatus could physically contain). This artefact was corrected by image translations based on the relationship between the false water thickness value and the distance moved by the sample. The implementation of this correction method led to a significant reduction in false water thickness (to ∼0.04 cm). Furthermore, to account for inaccuracies in pixel intensities due to the scattering effect and higher harmonics, a calibration technique was introduced for the liquid water X-ray attenuation coefficient, which was found to be 0.657 ± 0.023 cm(-1) at 20 keV. The work presented in this paper provides valuable tools for artefact compensation and accuracy improvements for dynamic synchrotron X-ray imaging of fuel cells.

Modeling the Effect of Fibre Surface Morphology on Liquid Water Transport in Polymer Electrolyte Membrane Fuel Cell Gas Diffusion Layers

In this work, we present a novel methodology for incorporating the effect of fibre surface morphology on liquid water transport in polymer electrolyte membrane fuel cell gas diffusion layers (GDLs). Roughness features presented on the surface of the fibre are analysed using atomic force microscopy and are found to significantly impact the capillary pressure of liquid water pathways propagating through the GDL. A threshold capillary pressure was defined as the largest capillary pressure exhibited by the liquid water phase during the invasion of the throat. The threshold capillary pressures observed in the presence of roughness features are significantly greater than those in the absence of roughness features. Two-dimensional circumferential roughness models in cylindrical and converging-diverging throats are established, and an interfacial meniscus advancing algorithm is presented to determine the resulting threshold capillary pressures required for liquid water penetration. Revised Young–Laplace equations, which are particularly useful for pore network modeling, are suggested for calculating threshold capillary pressures that account for the effect of the roughness of throats with intrinsic contact angles greater than

Feasibility of combining electrochemical impedance spectroscopy and synchrotron X-ray radiography for determining the influence of liquid water on polymer electrolyte membrane fuel cell performance

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In situ analysis of voltage degradation in a polymer electrolyte membrane fuel cell with a dead-ended anode

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In operando measurements of liquid water saturation distributions and effective diffusivities of polymer electrolyte membrane fuel cell gas diffusion layers

In this work, the change of liquid water preferential pathways through PEM fuel cell Gas Diffusion Layers (GDL) with ex situ devices is investigated. A capillary network constituted of two connected micro channels is first developed. It is shown that once the larger channel has been invaded, the pressure variation due to the growth of the water droplets at the channel tip enables the liquid water to invade the smaller capillary channel. At the end, the liquid preferential path is modified. This result is then generalized considering a real GDL. Liquid water is injected through the GDL to a micro channel, and changes in liquid water pathways are observed after several hours of operations. The reported experimental observations show that pressure-induced dynamic transport due the water droplet eruption in the channel has to be taken into account to predict the preferential pathway after long time of fuel cell operation.