Imaging Liquid Water in a PEFC with High-Energy X-Ray Compton Scattering

Abstract

Water management is important for stable operation of PEFCs (Polymer Electrolyte Fuel Cells), since the proton conductivity depends on water content and excessive water hinders electrochemical reactions. As the durability of PEFC has become a major issue, the correlative behavior between liquid water and cerium oxides (radical scavengers) is drawing much attention. Till now, the water content and its inhomogeneous distributions have been reported by neutron radiography and X-ray computed tomography (CT). In this paper, we present a high-energy Compton scattering imaging (CSI) technique for non-destructive observation of liquid water in PEFC.The advantage of high-energy CSI over X-ray CT is that the CSI technique has direct access to a two-dimensional cross section inside a PEFC without its rotation. The radiation damage on polymer electrolyte membranes is negligibly small since the photoelectric absorption is substantially reduced at such high-energy X-rays. Although high-energy X-ray CT is not sensitive to light-element materials, X-ray Compton scattering has its sensitivity to light elements.Figure 1 shows the cross-sectional images of GDL (Gas Diffusion Layer) materials and liquid water [1]. The GDL materials are made of porous carbon fibers and carbon composites with Teflon treatment, TGP-H-300 (TORAY Industries, Inc., Tokyo, Japan). The area of the cross sections is 2mm x 2mm, and its thickness is 10μm. The spatial resolution is 75 μm. Figure 1(a) shows the image of dry GDL materials, displaying the distribution of carbon fibers and carbon composite, and Figure 1(b) does the difference image between dry and wet, representing the liquid water distribution. Negative contributions are observed in the carbon fiber and carbon composite region, which indicates possible interactions between the GDL materials and liquid water.In this presentation, applications to a model cell under operation are also presented, together with correlation mappings of liquid water and cerium. The capability of CSI for vehicles’ PEFCs (TOYOTA MIRAI) is also discussed.This work was performed under the NEDO FC-Platform project.[1] N. Tsuji et al., Appl. Sci. 11, 3851 (2021)Figure Caption:Fig.1: Cross-sectional images of GDL materials and liquid water. Figure 1