Microstructure-property relationships in a gas diffusion layer (GDL) for Polymer Electrolyte Fuel Cells, Part I: effect of compression and anisotropy of dry GDL

Holzer, Lorenz; Pecho, Omar; Schumacher, Jürgen; Marmet, Philip; Stenzel, Ole; Büchi, Félix N.; Lamibrac, Adrien; Münch, Beat

doi:10.1016/j.electacta.2017.01.030

Cited by 79 publications

(39 citation statements)

References 37 publications

(97 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…it corresponds to the r 50 value from cumulative MIP-PSD curve). The cPSD and MIP-PSD methods were both introduced by Münch and Holzer [34], and the two different PSD principles were illustrated in part I [1].…”

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

confidence: 99%

“…In part I [1] this approach was then adapted specifically for the fibrous microstructure of GDL in PEFC, including special treatment of anisotropic features such as the elliptical shape of bottleneck cross-sections (specific case for transport in ip direction). In part I, the methods were then also applied for the study of effective properties in a dry GDL, including gas diffusivity (D eff ) and intrinsic permeability (k dry ) of the pores as well as electric conductivity (s eff ) of the solids.…”

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

confidence: 99%

“…For the dry GDL material (SGL 25BA) the microstructureproperty relationships were investigated in great detail in a previous study (part I) [1]. However, under operating conditions the GDL on the cathode side is usually not dry.…”

Section: Introductionmentioning

confidence: 99%

“…These methods were introduced in previous studies mainly for sintered, isotropic materials [13][14][15][16][17], but they were recently adapted specifically for the fibrous, anisotropic GDL materials in part I [1]. In the present study we apply these adapted methods for the study of microstructure effects in wet GDL, using 3D data from in-situ tomography experiments.…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

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

Self Cite

View full text Add to dashboard Cite

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.

show abstract

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

confidence: 99%

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

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

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

Self Cite

View full text Add to dashboard Cite

show abstract

“…The technique has become a powerful tool to describe morphology and study transport properties inside complex structures like GDLs, MPLs, and catalyst layers. [29][30][31][32][33][34][35][36][37] For example, Epting and Litster 30 used microscale X-ray CT to characterize the morphology of the GDL and provide detail analysis of the local oxygen concentration inside the GDL. Hong et al 31 combined nanoscale X-ray CT with the data from electrochemical diagnostics to enhance the understanding of materials and electrode designs for fuel cell particular under reversal tolerance anode.…”

mentioning

confidence: 99%

Micro-Scale Analysis of Liquid Water Breakthrough inside Gas Diffusion Layer for PEMFC Using X-ray Computed Tomography and Lattice Boltzmann Method

Satjaritanun

Weidner

Hirano

et al. 2017

J. Electrochem. Soc.

View full text Add to dashboard Cite

The main objective of this work is to predict the breakthrough pressure of liquid water transport through the gas diffusion layer (GDL) and/or micro porous layer (MPL) used in polymer electrolyte membrane fuel cells. The integration of structural GDL and MPL with Lattice Boltzmann Method is primary focused. The numerical predictions are also compared with experimental data. The interaction between liquid phase and different surface treatments of solid structures controls the evolution of liquid water and the change of capillary pressure. The geometries of GDLs and MPLs were obtained by three dimensional reconstructed micro-structure images from both nanometer and micrometer-scaled high spatial resolution X-ray computed tomography (CT). The predictions of water breakthrough pressure agree with the data observed in the experiment. They also reveal that the breakthrough pressure and liquid water evolution inside the GDL samples are different when the wetting properties of GDL and/or MPL are changed. The detailed microporous property can be obtained using high spatial resolution image from nanometer-scaled X-ray CT, a.k.a. Nano X-ray CT. Meanwhile, images from micrometer-scaled X-ray CT, a.k.a. Micro X-ray CT, give proper field of view to cover complete vision of porous materials, including cracks in the MPL. The enhancement of the transport of liquid water and reactant gases in polymer electrolyte membrane fuel cells (PEMFCs) is a critical subject that has been greatly studied due to its critical importance to fuel cell performance at high current densities.1-3 The liquid transport and the concurrent two-phase flow in the gas diffusion layer (GDL) and micro porous layer (MPL) are the most widely studied. In general GDL materials for PEMFCs are made of carbon fiber based cloths and paper. These materials are typically porous to allow for the transport of reactant gases to the catalyst layer as well as transport of condensed water from the catalyst layer. To accelerate the removal of liquid water, GDLs are usually impregnated with non-wetting polymer such as polytetrafluoroethylene (PTFE) to create hydrophobic characteristics. Further, a thin MPL which consists of carbon powder and polymer binders is applied to the GDL side facing the catalyst layer in the membrane electrode assembly (MEA) to further increase cell performance and mechanical stability. The complex structural and chemical heterogeneity of the GDL and MPL make studying the transport of liquid water and obtaining the solution for mass transport losses substantially complicated. 4,5 Many researchers have studied the transport of liquid water through the GDL and MPL in order to develop an understanding of the resistance of reactant gas transport due to water accumulation.6-27 These included the observation of vapor condensation and liquid breakthrough in a GDL using an environmental scanning electron microscope (SEM).13,14 They proposed a treelike transport mechanism in which micro-droplets condensed from vapor agglomerate to form macro-droplets which even...

show abstract

Effect of cell compression on the performance of a non–hot‐pressed MEA for PEMFC

2019

View full text Add to dashboard Cite

In this study, effect of cell compression on the performance of a non-hot press membrane electrode assembly (MEA) for a polymer electrolyte membrane fuel cell (PEMFC) is presented. The MEA is made without hot pressing, by carefully placing the gas diffusion electrodes (GDEs) and a membrane in a fuel cell fixture. Cell performance is assessed at five different compression ratios between 3.6% and 47.8%. It has been shown that ohmic resistance of the cell, mass transport resistance of reactants, charge transfer resistance at electrode and overall cell performance are strongly dependent on the cell compression. On increasing the cell compression gradually, cell performance improves initially, reaches the best and then deteriorates. The cell performance is assessed at fully humidified condition and at dry condition. Optimum cell performances are obtained at compression ratios of 14.2% and 25.7% for 100% relative humidity (RH) and 50% RH, respectively. It is also found that the cell with proper compression and at fully humidified conditions can deliver similar performance to a conventional hot-pressed MEA. Finally, it is shown that after the tests, GDEs can be peeled out and the membrane inspection can be done as a post experimental analysis.

show abstract

Microstructure-property relationships in a gas diffusion layer (GDL) for Polymer Electrolyte Fuel Cells, Part I: effect of compression and anisotropy of dry GDL

Cited by 79 publications

References 37 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

Micro-Scale Analysis of Liquid Water Breakthrough inside Gas Diffusion Layer for PEMFC Using X-ray Computed Tomography and Lattice Boltzmann Method

Effect of cell compression on the performance of a non–hot‐pressed MEA for PEMFC

Contact Info

Product

Resources

About