Recent Progress in Liquid Water Visualization of Polymer Electrolyte Fuel Cells Elucidated By Synchrotron X-Ray and Pulsed Neutron Sources
Authors: Yoshimune Wataru , Higuchi Yuki , Kato Akihiko , Song Fangzhou , Hibi Shogo , Yamaguchi Satoshi , Matsumoto Yoshihiro , Hayashida Hirotoshi , Shinohara Takenao , Kato Satoru 
Published: December 2024

The formation, accumulation, evaporation, and elimination of water in polymer electrolyte fuel cells (PEFCs) is one of the key features for achieving high power density. The oxygen reduction reaction at the cathode catalyst surface produces water as a by-product. Some of the produced water is discharged from the PEFC through the gas flow channels, while the rest accumulates in the catalyst layer (CL) and gas diffusion layer (GDL). The accumulated water in the porous media inhibits the oxygen supply to the cathode catalyst surface, leading to an increase in the concentration overpotential. Therefore, we have developed water visualization techniques using synchrotron X-rays and pulsed neutrons [1–9]. The three-dimensional water transport behavior in GDLs has been reported by operando X-ray computed tomography (CT) [1]. The water condensation behavior in GDLs has been demonstrated by ex-situ X-ray micro-CT [2] and nano-CT [4]. The dynamic water behavior in GDLs induced by water injection has been studied by ex-situ X-ray high-speed time-resolved X-ray micro-CT [3]. The complementary use of operando X-ray and neutron radiography revealed the water drainage mechanism of large-sized PEFCs [5]. The water accumulation behavior in GDLs has been studied by operando X-ray radiography [6–8]. The water behavior in large-sized PEFCs during cold start has been clarified by the water/ice identification technique using operando pulsed neutron imaging [9].

In this talk, we will briefly introduce our previous achievements and present a recent progress in new results: water visualization in Pt-based CLs and thawing behavior in large-sized PEFCs during cold start. In the first topic, water visualization imaging was performed using operando synchrotron X-ray radiography. In general, the strong X-ray absorption of Pt results in low transmittance, which limits water visualization in Pt-based CLs. To overcome this problem, we reviewed our cell configuration and developed a new in-house cell dedicated to the observation of water distribution in cathode CLs. In the second topic, water visualization imaging was performed using operando pulsed neutron radiography. We focused on the current recovery behavior observed during cold start in short stacks. The temperature condition in short stacks during cold start was reproduced in a single cell by rapid heating with an in-house external heater.

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