Accounting for low-frequency synchrotron X-ray beam position fluctuations for dynamic visualizations

Abstract

Synchrotron X-ray radiography on beamline 05B1-1 at the Canadian Light Source Inc. was employed to study dynamic liquid water transport in the porous electrode materials of polymer electrolyte membrane fuel cells. Dynamic liquid water distributions were quantified for each radiograph in a sequence, and non-physical liquid water measurements were obtained. It was determined that the position of the beam oscillated vertically with an amplitude of ~25 µm at the sample and a frequency of ~50 mHz. In addition, the mean beam position moved linearly in the vertical direction at a rate of 0.74 µm s(-1). No evidence of horizontal oscillations was detected. In this work a technique is presented to account for the temporal and spatial dependence of synchrotron beam intensity, which resulted in a significant reduction in false water thickness. This work provides valuable insight into the treatment of radiographic time-series for capturing dynamic processes from synchrotron radiation.

Synchrotron Investigation of Microporous Layer Thickness on Liquid Water Distribution in a PEM Fuel Cell

“…Half of the active area (at the centre) was analyzed where the beam intensity distribution provided the highest quality of image capture. 21 As discussed in the reference, 21 the distribution of X-ray beam intensity across the imaging region was non-uniform. The intensity of the beam was highest at the central region and decreased away from this region.…”

“…14,20,21 The outlets of the channels were diverted away from the beam path in a "Y" configuration ( Figure 2) in order to minimize the liquid water accumulation in the corner regions of the channels. By diverting the outlets, the beam intensity across the ribs of the flow field was evenly distributed.…”

“…The fluctuation of beam position was accounted for using an algorithm presented in our previous work. 21 Five consecutive frames (over a period of 15 s) were averaged to mitigate artifacts and noise for all image analysis. Half of the active area (at the centre) was analyzed where the beam intensity distribution provided the highest quality of image capture.…”

“…14,16,[18][19][20][21][22][23][24][25][26] A synchrotron facility generates a collimated and monochromatized X-ray beam at high intensities and is capable of rendering images at micron-scale resolutions. Several groups have successfully demonstrated this capability and provided valuable insight on the in situ transport behavior of fuel cells.…”

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

“…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].…”