Resolving macro- and micro-porous layer interaction in polymer electrolyte fuel cells using focused ion beam and X-ray computed tomography

Wargo, Eric A.; Schulz, Volker P.; Cecen, Ahmet; Kalidindi, Surya R.; Kumbur, E. Caglan

doi:10.1016/j.electacta.2012.09.008

Cited by 70 publications

(46 citation statements)

References 48 publications

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“…Spatial resolution, temporal resolution as well as imaging contrast are now sufficiently high, so that it becomes possible to follow the water migration on the pore scale based on in-situ X-ray tomographic microscopy experiments [28][29][30][31][32][33]. Using these methods, the mechanisms that lead to a specific water distribution and associated liquid permeability can be investigated.…”

Section: Description Of Liquid Permeability Based On 3d-analysismentioning

confidence: 99%

Microstructure-property relationships in a gas diffusion layer (GDL) for Polymer Electrolyte Fuel Cells, Part II: pressure-induced water injection and liquid permeability

Holzer

Pecho

Schumacher

et al. 2017

Electrochimica Acta

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Keywords:Gas diffusion layer (GDL) X-ray tomographic microscopy anisotropy liquid permeability short-range effect (SRE) A B S T R A C TThe performance of polymer electrolyte fuel cells (PEFC) strongly depends on a controlled water management within the porous layers. For this purpose we investigate liquid water transport in a commercial gas diffusion layer (SGL 25BA) on the pore scale. X-ray tomography experiments combined with pressure-induced water injection provide 3D images of the liquid water distribution inside the GDL at incremental pressure steps between 0 and 100 mbar.The breakthrough behavior of the liquid phase is highly anisotropic. In through-plane (tp) direction first bubble points appear at the outlet plane already at 5 mbar and the 'breakthrough' then evolves continuously over an extended pressure range up to > 30 mbar. For in-plane (ip) direction the breakthrough is discontinuous and takes place at 27 mbar. Simulations of the intrusion process reveal that the different breakthrough behaviors are mainly triggered by different ip-and tp-transport distances. Short tp-transport distances through the thin gas diffusion layer (ca. 100 mm) are responsible for the characteristic continuous tp-breakthrough behavior, which is thus attributed to a so-called shortrange effect.Dedicated methods for 3D-image analysis adapted to fibrous GDL microstructures were presented in part I. With these methods we quantify all microstructure characteristics that are relevant for liquid permeability. These characteristics of pore and liquid phases include size distributions of bulges and bottlenecks, connectivity, effective volume fractions, geodesic tortuosity, constrictivity and hydraulic radius. Quantitative relationships are established between these microstructure characteristics and the liquid permeability, which provide a better understanding of the underlying microstructure limitations for injection and liquid transport.For the in-plane direction the liquid permeability is limited to roughly a similar extent by tortuosity, constrictivity and effective volume fraction. In contrast, for through-plane direction relatively low volume fractions of the liquid phase put stronger limitations to the liquid permeability than tortuosity, constrictivity and hydraulic radius.The curves for relative permeability vs. saturation (and vs. capillary pressure, respectively) achieved from 3D-analysis reveal complex but characteristic (reproducible) shapes with concave, linear and convex segments. The shape of these segments can be attributed to distinct microstructure effects. In contrast, the conventional macroscopic descriptions from literature cannot capture these complex shapes and the underlying microstructure effects. Future investigations with different GDL materials are necessary in order to understand whether these complex shapes for the relative permeability represent a general feature of gas diffusion layers or if they are specific to the investigated SGL material.

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Section: Description Of Liquid Permeability Based On 3d-analysismentioning

confidence: 99%

Microstructure-property relationships in a gas diffusion layer (GDL) for Polymer Electrolyte Fuel Cells, Part II: pressure-induced water injection and liquid permeability

Holzer

Pecho

Schumacher

et al. 2017

Electrochimica Acta

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“…When an MPL is coated onto the carbon fiber substrate, the MPL intrudes into the carbon fiber substrate [90,[94][95][96][97], therefore there is not a clear physical boundary between these layers. The The volume fraction of void space within a porous material is defined as the porosity.…”

Section: Gdl Porosity Characterization By X-ray Micro-computed Tomogrmentioning

confidence: 99%

Liquid water saturation and oxygen transport resistance in polymer electrolyte membrane fuel cell gas diffusion layers

Muirhead

Banerjee

George

et al. 2018

Electrochimica Acta

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In this thesis, the relative humidity (RH) of the cathode reactant gas was investigated as a factor which influences gas diffusion layer (GDL) liquid water accumulation and mass transport-related efficiency losses over a range of operating current densities in a polymer electrolyte membrane (PEM) fuel cell. Limiting current measurements were used to characterize fuel cell oxygen transport resistance while simultaneous measurements of liquid water accumulation were conducted using synchrotron X-ray radiography. GDL porosity distributions were characterized with micro-computed tomography (μCT). The work presented here can be used by researchers to develop improved numerical models to predict GDL liquid water accumulation and to inform the design of next-generation GDL materials to mitigate mass transport-related efficiency losses. This work also contributes an extensive set of concurrent performance and liquid water visualization data to the PEM fuel cell field that can be used for validating multiphase transport models.iii

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“…There has been a surge over the past few years in use of pore-scale model and tomography to simulate various flow and transport processes in PEM fuel cells, including twophase flow [18], oxygen diffusion and reduction in cathode CL [19], and estimating effective transport parameters [11,20]. These have substantially improved our understanding of some fundamental processes occurring in the cell [17], which would remain unknown otherwise [21].…”

Section: Introductionmentioning

confidence: 99%

“…For example, using X-ray computed tomography or focused ion beam/scanning electron microscopy (FIB/SEM), one can visualise the interior structure of a porous material at resolutions as fine as a few nanometres [12][13][14][15][16][17]. There has been a surge over the past few years in use of pore-scale model and tomography to simulate various flow and transport processes in PEM fuel cells, including twophase flow [18], oxygen diffusion and reduction in cathode CL [19], and estimating effective transport parameters [11,20].…”

Section: Introductionmentioning

confidence: 99%

Modelling water intrusion and oxygen diffusion in a reconstructed microporous layer of PEM fuel cells

Zhang

Gao

Ostadi

et al. 2014

International Journal of Hydrogen Energy

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The hydrophobic microporous layer (MPL) in PEM fuel cell improves water management but reduces oxygen transport. We investigate these conflict impacts using nanotomography and porescale modelling. The binary image of a MPL is acquired using FIB/SEM tomography. The water produced at the cathode is assumed to condense in the catalyst layer (CL), and then builds up a pressure before moving into the MPL. Water distribution in the MPL is calculated from its pore geometry, and oxygen transport through it is simulated using pore-scale models considering both bulk and Knudsen diffusions. The simulated oxygen concentration and flux at all voxels are volumetrically averaged to calculate the effective diffusion coefficients. For water flow, we found that when the MPL is too hydrophobic, water is unable to move through it and must find alternative exits. For oxygen diffusion, we found that the interaction of the bulk and Knudsen diffusions at pore scale creates an extra resistance after the volumetric average, and that the conventional dusty model substantially overestimates the effective diffusion coefficient.

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Resolving macro- and micro-porous layer interaction in polymer electrolyte fuel cells using focused ion beam and X-ray computed tomography

Cited by 70 publications

References 48 publications

Microstructure-property relationships in a gas diffusion layer (GDL) for Polymer Electrolyte Fuel Cells, Part II: pressure-induced water injection and liquid permeability

Microstructure-property relationships in a gas diffusion layer (GDL) for Polymer Electrolyte Fuel Cells, Part II: pressure-induced water injection and liquid permeability

Liquid water saturation and oxygen transport resistance in polymer electrolyte membrane fuel cell gas diffusion layers

Modelling water intrusion and oxygen diffusion in a reconstructed microporous layer of PEM fuel cells

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