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Influence of Channel-Land Architecture and Diffusion Media Tortuosity on Liquid Water Content of Polymer Electrolyte Fuel Cells

Jacob Lamanna (Mechanical, Aerospace, and Biomedical Engineering Department, University of Tennessee)

Polymer electrolyte fuel cells (PEFC) are seen as a viable replacement for the internal combustion engine for the automotive market due to its high efficiency and carbon free operation. PEFCs must maintain high performance and reliability to be competitive with internal combustion engines, both of which are greatly influenced by the water content of the cell. This work uses high-resolution neutron radiography to image the through-plane water content of an operational fuel cell based on actual automotive industry hardware. The 10 µm microchannel plate detector at the National Institute of Standards and Technology provides high enough spatial resolution to resolve the through-plane liquid water profile in 200 µm thick diffusion media. Temperature, pressure, and relative humidity (concentration) gradients were imposed on several cell configurations to determine individual gradient influences on water content for each configuration. Symmetric land widths (0.5|0.5 mm and 0.25|0.25mm anode|cathode) and asymmetric land widths (1.5|0.5mm and 1|0.25mm anode|cathode), high tortuosity anode diffusion media, and degraded materials were tested. The asymmetric land width architecture with 1.5 mm anode and 0.5 mm cathode land widths results in significant water accumulation in the anode diffusion media with saturation values of up to ~50%. Anode water content was found to change substantially with imposed pressure or concentration gradient, whereas the cathode saturation profile remained relatively consistent. This large increase in water anode water content was found to decrease significantly with the use of symmetric land widths, high tortuosity anode diffusion media, and age of the material. This indicates that large anode land ratio and loss of PTFE have strong thermal effects that drive water transport along the thermal gradient and that tailored diffusion media properties can be effectively used to control cell water content.

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