Observation of water droplets in microporous layers for polymer electrolyte fuel cells by X-ray computed nano-tomography

Abstract

An X-ray computed nano-tomography (nano-CT) system has been established at the BL33XU beamline of SPring-8. The optical system consists of pseudo-Köhler illumination with a sector condenser zone plate, an apodization Fresnel zone plate as the objective lens, and a Zernike phase plate. The imaging detector is a fiber-coupling type X-ray camera. The performance of the X-ray nano-CT system was confirmed by imaging an X-ray test chart. The system was subsequently applied to the observation of a microporous layer for polymer electrolyte fuel cells and a simulated microporous layer including liquid water. The nano-CT system, which can perform a computed tomography measurement in less than 4 min, allowed visualization of a spherical water droplet produced in the microporous layer. In the present study, the shape of water droplets in a nanoscale porous structure is investigated.

Comprehensive Analysis of Wettability in Waterproofed Gas Diffusion Layers for Polymer Electrolyte Fuel Cells

“…However, this approach only provides information about the surface hydrophobicity, including the roughness factor. Other laboratory techniques, such as the Washburn and Wilhelmy methods, can be applied to measure the internal GDL wettability. − Moreover, cyclic voltammetry (CV) measurements facilitate the assessment of internal GDL wettability based on the surface area of the wet GDL, as determined through the formation of an electrical double layer at the GDL/electrolyte interface. − Advanced imaging techniques, including computed tomography (CT) ,− and radiography ,− using X-ray and neutron sources, are advantageous for elucidating the internal contact angle and water saturation level, respectively, in wet GDLs within PEFCs. Herein, we present a comprehensive analysis encompassing the pore size distribution, porosity, external and internal wettabilities, water saturation, and flooding tolerance of carbon papers with various PTFE contents to provide insights into the effective design of waterproofed carbon papers as cathode GDLs in PEFCs.…”

Insights into Oxygen Transport Properties of Partially Saturated Gas Diffusion Layers for Polymer Electrolyte Fuel Cells

“…Advances in technology and methodology have made it accessible to obtain high-resolution three-dimensional (3D) images of GDL structures. Many studies have been reported on extracting porosity and tortuosity as GDL structural parameters to understand the transport limitations in a dry GDL. ,,− Recently, 3D images of nanoscale particles and pores within an MPL have been taken using focused ion beam scanning electron microscopy (FIB-SEM) , and synchrotron X-ray computed tomography (XCT). ,−, The captured high-resolution 3D images provide the porosity of GDLs but not the “real” tortuosity toward the effective oxygen diffusion path. Therefore, tortuosity is often approximated as a function of porosity: ε/τ = ε γ , where γ is the empirical parameter depending on the structure. , …”

“…6,8,11−16 Recently, 3D images of nanoscale particles and pores within an MPL have been taken using focused ion beam scanning electron microscopy (FIB-SEM) 11, 12 and synchrotron X-ray computed tomography (XCT). 11,14−, 16 The captured high-resolution 3D images provide the porosity of GDLs but not the "real" tortuosity toward the effective oxygen diffusion path. Therefore, tortuosity is often approximated as a function of porosity: ε/τ = ε γ , where γ is the empirical parameter depending on the structure.…”