Elucidating the Role of Flow Fields in Bubble Removal from Porous Transport Layers

Abstract

Accelerating bubble removal from the porous transport layer (PTL) will be the key to reaching high current densities and cell efficiencies for polymer electrolyte membrane (PEM) water electrolyzers by improving catalyst utilization through reduced bubble accumulation for enhanced water transport to reach reaction sites 1,2. Previous studies have reported non-uniform bubble distributions within the PTL, where bubble saturation under the flow field lands was higher than that under the channel 3–5. This bubble distribution heterogeneity was attributed to the PTL/flow field interface and PTL/catalyst layer interface, which caused non-uniform outlet and non-uniform inlet conditions for bubble transport within the PTL, respectively. As such, determining the impact of the interfacial conditions on bubble removal from the PTL is critical for optimizing designs for next generation PTLs that need to exhibit low reactant mass transport resistances for PEM water electrolyzers.In this study, we elucidated the effects of the PTL/flow field interface on bubble transport in the PTL and specified the role of flow fields in bubble removal from the PTL. First, X-ray computed tomography (CT) was employed to reconstruct the microstructure of a titanium fibre-based PTL. Pore network modelling was then implemented to simulate and analyze the multiphase flow behaviour within the PTL under two kinds of outlet boundary conditions, i.e., with and without a flow field. We showed a dramatic non-uniform bubble distribution within the PTL when using an outlet condition with a flow field, while a uniform bubble distribution occurred in the PTL when using an outlet condition without a flow field. We attributed this to the existence of flow fields that lead to longer gas transport pathways through the PTL regions under the flow field lands. This study demonstrates the effects of flow fields on hindering bubble transport within the PTL and informs the need of tailored designs of the PTL/flow field interface for accelerating bubble transport in the PTL. References J. K. Lee and A. Bazylak, Joule, 5, 19–21 (2021).S. Yuan et al., Prog. Energy Combust. Sci., 96, 101075 (2023).J. K. Lee et al., Cell Reports Phys. Sci., 1, 100147 (2020).C. H. Lee et al., J. Power Sources, 446, 227312 (2020).S. De Angelis et al., J. Mater. Chem. A, 9, 22102–22113 (2021).