Calibrating the X-ray attenuation of liquid water and correcting sample movement artefacts duringin operandosynchrotron X-ray radiographic imaging of polymer electrolyte membrane fuel cells

Abstract

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.

Liquid water saturation and oxygen transport resistance in polymer electrolyte membrane fuel cell gas diffusion layers

“…Synchrotron X-ray radiography offers high spatial and temporal resolutions (less than 10 μm and less than 10 s, respectively) [38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57]. Though X-ray photons are not as sensitive as a neutron beam to the presence of liquid water, Chevalier et al [29] demonstrated that synchrotron X-ray radiography can achieve similar accuracy to neutron radiography with a high level of precision.…”

“…The X-ray energy level was selected to maximize transmitted photon intensity while avoiding beam contamination by higher harmonic X-ray energy levels [44,59]. A schematic of the experimental set-up is shown in Figure 3 the signal-to-noise ratio without overexposing any pixels.…”

“…is the attenuation coefficient of water, which was calculated for our experimental set-up using a calibration technique described by Ge et al [44].…”

“…Though X-ray photons are not as sensitive as a neutron beam to the presence of liquid water, Chevalier et al [29] demonstrated that synchrotron X-ray radiography can achieve similar accuracy to neutron radiography with a high level of precision. Recent works have improved the accuracy and reliability of this technique for PEM fuel cell visualizations by establishing methodologies for correcting beam position movement artifacts [58], calibrating the attenuation coefficient of liquid water and correcting sample movement artifacts [44], and considering photon scattering and harmonics [59]. In addition, the fast temporal resolutions possible with synchrotron X-ray radiography allow for dynamic visualizations of transient liquid water behaviour [60,61] and enable high-resolution in-situ tomography to resolve liquid water saturation in 3-D [48,52,62].…”

“…The quantity of liquid water was calculated by applying the Beer-Lambert Law, which relates the attenuation of light in a material to its thickness [44,45,59]. = ln ( ) (3.1)…”