The effect of non-uniform compression and flow-field arrangements on membrane electrode assemblies - X-ray computed tomography characterisation and effective parameter determination

Abstract

The performance of the of polymer electrolyte membrane (PEM) fuel cell is governed by a complex interaction of the structure of the membrane electrode assembly (MEA), cell compression, and operating parameters. Adequate cell compression for improved current collection and gas sealing, can structurally deform MEA with adverse consequences. Nonuniform MEA compression exerted by the flow-field design and arrangement induces heterogeneous transport properties. Hence, understanding morphological evolution and effective transport properties as an effect of MEA compression is an important factor for improving fuel cell performance and durability. In this paper, an X-ray computed tomography study of the entire MEA compression is presented, comprising of gas diffusion and microporous layers, catalyst layers, and the electrolyte membrane, subjected to non-uniform compression under two distinct flow-field arrangements. This study presents a comprehensive dataset of the heterogeneous effective properties required for robust computational modelling; including porosity, permeability, tortuosity, and diffusivity, along with the extent of blocking of the flow channel due to cell compression and effect of compression on the structural properties of the membrane.

Modelling of redox flow battery electrode processes at a range of length scales: a review

“…In fuel cells, this uneven compression can affect the ow, ohmic resistance and pressure drop. 169 Similarly, uneven compression has also been observed in RFBs. [170][171][172][173][174] Numerical simulations indicate that the uneven compression and intrusion of the porous electrode into the ow channel increased the ow velocity in the channel, enhancing transport processes and electrochemical performance.…”

Performance Studies of Proton Exchange Membrane Fuel Cells with Different Flow Field Designs – Review

“…The high interfacial contact area between the channel surface and the carbon paper (GDL) ending with an exponential increase in the contact at higher compression. These will significantly affect the relationship between the contact resistance and cell performance [173] . Xing et al.…”

In Situ and Operando Characterization of Proton Exchange Membrane Fuel Cells

“…Recently, the impact of flow-field misalignment during assembly into a single cell has also been highlighted. [66] In a bespoke configuration using in situ X-CT with a compression stage, slight misalignment of the anodic and cathodic lands has been observed to cause acute stress to the gasdiffusion electrode. Such deformation leads to partial blockage of the flow-field, alongside localized thinning of the electrolyte membrane, which could induce cracks during operations (Figure 4c).…”

“…Such deformation leads to partial blockage of the flow-field, alongside localized thinning of the electrolyte membrane, which could induce cracks during operations (Figure 4c). [66] The role of compression in stretching the membrane electrode assembly has been investigated, revealing a lateral expansion of over 1 mm. [67] Modeling extracted from these results highlights that the gap between the membrane electrode assembly and the gasket can enhance/hinder gas diffusion by creating another gas pathway.…”