Abstract
There is a potential to increase the zero-emission polymer electrolyte fuel cell (PEFC) efficiency through high power density operation. However, water management issues become significant under these conditions, necessitating improved water management strategies [1]. As a precursor, understanding of liquid water distribution is instrumental to developing optimal water management strategies.
Various techniques including neutron imaging, electron microscopy, and X-ray imaging have been used to study liquid water transport in fuel cells. Of these, the X-ray computed tomography (XCT) method has provided unprecedented insights gained through in-operando visualization, yielding 3-dimensional (3D) information [2, 3]. The 3D grayscale data set is obtained by first acquiring multiple projections of the sample at different angles which are then reconstructed to yield a 3D representation. The 3D representation may then be processed to segment features such as liquid water and other features of interest [3, 4]. However, the acquisition of such 3D datasets typically takes several hours on a lab-scale XCT instrument [5]. This may sometimes result in a dataset that is difficult to interpret if the imaged sample evolves significantly during the acquisition time. Furthermore, phenomena of interest, such as liquid water distribution may sometimes be challenging to capture with 3D datasets. In this work, we therefore explore the use of transmission radiograph imaging to further understand the distribution of liquid water in an operating fuel cell.
The method developed involves the analysis of in-operando transmission images within the framework of the X-ray attenuation laws to provide qualitative, as well as quantitative saturation and liquid water distribution information. Sequential images of a miniaturized operating fuel cell were acquired at 0- and 90-degree angles to the fuel cell plane within a laboratory XCT equipment, while cell operational conditions were controlled by an external fuel cell test station. This approach trades off 3D information for short time scans afforded by 2D acquisition procedure, enabling the identification of liquid water droplet breakthrough dynamics at the cathode gas diffusion layer, as shown in Figure 1. The observed liquid water breakthrough yields new findings on the nature of liquid water distribution in the flow channels, often elusive to 3D approaches. Methods and analysis developed may therefore be used to augment information derived from 3D visualization methods.
Acknowledgments
Funding for this research was provided by the Natural Sciences and Engineering Research Council of Canada, Ballard Power Systems, Canada Foundation for Innovation, British Columbia Knowledge Development Fund, Canada Research Chairs.
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Figure 1