A study conducted by Wataru Yoshimune et al. was published in the Journal of Power Sources.

 

Fuel cell electric vehicles emit only water during operation. Under low-temperature conditions, however, if water generated during driving remains inside the electrodes, it may freeze after shutdown and affect restart performance. To address this, fuel cell vehicles generally employ a control process known as gas purging, in which gas is supplied at shutdown to remove internal water and enhance restart reliability in cold environments. In practical systems, the completion of purging has been assessed, for example, by using the electrical resistance of the proton exchange membrane as an indicator. This approach serves as an effective and practical indirect metric, based on estimating the internal water distribution, including water remaining in the porous gas diffusion layer within the electrodes. To further strengthen the validity of such evaluations, fundamental knowledge obtained through direct visualization of residual water inside the gas diffusion layer has been required.

 

In this study, we used in situ synchrotron X-ray radiography to directly observe water evaporation behavior inside a polymer electrolyte fuel cell during gas purging. We clearly demonstrated for the first time that water preferentially accumulates under the ribs of the gas diffusion layer and is highly resistant to evaporation, even under gas flow. In addition, water slugs remaining in the flow channels were found to hinder vapor transport. These insights provide important guidance for designing more effective gas purging strategies during shutdown. This research is expected to contribute to the development of fuel cell vehicles that can be safely and reliably used even in cold climates.

 

 

Title: In Situ Observation of Water Evaporation in Gas Diffusion Layers of Polymer Electrolyte Fuel Cells

Authors: Yoshimune, W., Kato, A., Hayakawa, T., Yamaguchi, S., Kato, S.

Journal Name: Journal of Power Sources

Published: November 1, 2025

https://doi.org/10.1016/j.jpowsour.2025.237896