Spatially Resolved Contact Pressure and Contact Resistance Measurements at the Gas Diffusion Layer: A Tool for PEM Fuel Cell Development

Butsch, Hanno; Roth, Christina; Ritzinger, Dietrich; Hoogers, Gregor; Bock, Achim

doi:10.1149/2.054206jes

Cited by 10 publications

(12 citation statements)

References 20 publications

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“…The distribution of electrical resistance is a clear indicator of non-uniform compression pressure distribution where pressure is high under the land and low under the channel. Result presented in this work is qualitatively similar to the one presented by Butsch et al 17 Such electrical resistance can cause non-uniform ohmic overpotential distribution. For example at uniform current generation of 2 A/cm 2 the ohmic loss can vary from 16 mV at the edge of land to 32 mV at the center of channel.…”

Section: Resultssupporting

confidence: 90%

Sources of Current Density Distribution in the Land-Channel Direction of a PEMFC

Shrivastava¹,

Tajiri²

2016

J. Electrochem. Soc.

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A proton exchange membrane fuel cell (PEMFC) was segmented to measure local current density, electrochemical surface area, and high frequency resistance (HFR) distribution in the land-channel direction at resolution of 350 μm. An in-house catalyst coated membrane of 3 mm × 3 mm active area was prepared to represent a small area in a larger scale cell with 1 mm land and channel widths. This design was employed to measure current density and HFR distribution at 60 • C with several different operating conditions. Local electrical resistance was also measured separately so that local protonic resistances can be discerned from local HFR. To analyze the effect of the land-channel geometry a method was developed to quantify the sources of current distribution, such as distributions of oxygen concentration at the electrode, oxygen transport resistance, cathode catalyst layer resistance, and membrane water content. Current density distribution is strongly correlated with the distribution of membrane water content and electrode resistance in dry condition, and oxygen concentration distribution in wet condition, while in moderate condition both oxygen concentration and water content in membrane are critical to the local current density distribution. The results imply the limitation of uniform condition assumption used in a differential cell study. Proton exchange membrane fuel cell (PEMFC) is an electrochemical reactor with three geometrical directions: flow channel (length scale 1 to 100 cm), land-channel (length scale 100 to 1000 μm), and through-plane (length scale 10 to 100 μm) directions. Because of the geometry of a PEMFC the distribution of reactants and products in these directions are highly inhomogeneous, as a result making current generation non-uniform. In order to study the local non-uniformities in the flow-channel direction, segmentation of a PEMFC to many differential cells is widely used. Here the differential cell means a fuel cell with small enough active area so that various conditions within the cell can be considered uniform along the flow channel direction. On the other hand, because of its relatively smaller length scale, variations in the land-channel direction are often neglected in most of such studies. However, due to the non-uniform transport length distribution from channel to catalyst layer in the land-channel direction, the differential cells aligned in the flow direction give only the averaged values over each differential cell, and therefore the local information in the land-channel direction cannot be captured.In a wet condition, for example, due to the land-channel geometry liquid water tends to distribute non-uniformly in gas diffusion layer (GDL). Many modeling studies present in literature have predicted liquid water distribution in land-channel direction.1-4 One example of such study is numerical investigation of liquid water saturation distribution in the land-channel direction of a flow field with 1 mm wide land and channel presented by Wang et al. 5 According to their findings, li...

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Section: Resultssupporting

confidence: 90%

Sources of Current Density Distribution in the Land-Channel Direction of a PEMFC

Shrivastava¹,

Tajiri²

2016

J. Electrochem. Soc.

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“…It is experimentally and theoretically evident that the contact pressure in the channel center is significantly lower than in the land area, because of an absent mechanical support in the channel area. 18,26,31 Furthermore, imaging studies show that under compression, the diffusion medium intrudes into the flow channel, creating a variation of local GDL thickness and porosity. 29,30 The present measurement confirms this trend: at C GDL of 20%, an average pressure of 1.1 MPa was measured, while the pressure at the land center is 1.3 MPa and 0.4 MPa at the channel center.…”

Section: Resultsmentioning

confidence: 99%

“…It has been reported that the ratio between land, channel, and average pressure is a strong function of the flow field dimensions, especially of the channel width and stiffness of the GDL material. 18,26,31 Unfortunately, for a low compression of 8%, no differentiation between channel and land pressure is possible from the pressure distribution image: due to the stiffness of the Prescale film itself, the image shows a very homogeneous distribution of the pressure. However in a real cell setup without a mechanically stabilizing layer, the trend of a significantly lower channel pressure compared to the average pressure shown in Figure 2a is also expected at C GDL of 8%.…”

Section: Resultsmentioning

confidence: 99%

“…Hence, the contact pressure between MPL and cathode electrode layer is only a small fraction of that under the land area as shown in Figure 2. 18,26,31 The pressure distribution across land and channel region is also illustrated in Figure 9. If the MPL loses its contact to the cathode electrode layer, water can accumulate on the more hydrophilic surface of the catalyst layer, which would lead to a similar effect as…”

Section: Discussionmentioning

confidence: 99%

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Influence of the Gas Diffusion Layer Compression on the Oxygen Transport in PEM Fuel Cells at High Water Saturation Levels

Simon

Hasché

Gasteiger

2017

J. Electrochem. Soc.

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The impact of the gas diffusion layer (GDL) compression on the oxygen transport is investigated in single cell assemblies at 50°C, RH = 77%, 200 kPaabs and under differential flow conditions. For this, the oxygen transport resistance at low and high current densities is determined by limiting current density measurements at various oxygen concentrations for GDLs with and without microporous layer (MPL). At small current densities (≤0.4 A cm−2), where no liquid water in the GDL/MPL is present, a linear increase of oxygen transport resistance with GDL compression is observed, with the GDL without MPL exhibiting a significantly lower transport resistance. For low compressions of ≈8%, we find that the oxygen transport resistance for the GDL with MPL is increasing disproportionately high in the high current density region (>1.5 A cm−2), where water condensation in the porous media takes place. A similar trend is observed for a GDL without MPL at a typical compression of 22%. Based on these results, we hypothesize that a developing liquid water film is hindering the oxygen diffusion at the interface between MPL and cathode, analogous to what is known to be formed on the cathode surface for GDLs without MPL.

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“…The analysis includes the effect of oxygen ) −1.09 mΩ cm 2 , characterized by low and high electrical contact resistances, respectively [89]. The influence of the electrical contact resistance between the diffusion medium and the membrane, R gdl/mem c , has been examined separately in one section, being neglected in the rest of the work, due to the large uncertainty concerning its value, with variations of more than one order of magnitude between authors [63,[99][100][101][102]. In first approximation, R gdl/mem c is modeled using a correlation similar to that for graphite BPPs, R gdl/mem c = 2Π(p gdl/mem c ) −0.8 mΩ cm 2 , except for the presence of a constant multiplicative factor Π that is freely varied.…”

Section: Geometry and Case Studiesmentioning

confidence: 99%

On the effect of operating conditions in liquid-feed direct methanol fuel cells: A multiphysics modeling approach

García-Salaberri

Vera

2016

Energy

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Spatially Resolved Contact Pressure and Contact Resistance Measurements at the Gas Diffusion Layer: A Tool for PEM Fuel Cell Development

Cited by 10 publications

References 20 publications

Sources of Current Density Distribution in the Land-Channel Direction of a PEMFC

Sources of Current Density Distribution in the Land-Channel Direction of a PEMFC

Influence of the Gas Diffusion Layer Compression on the Oxygen Transport in PEM Fuel Cells at High Water Saturation Levels

On the effect of operating conditions in liquid-feed direct methanol fuel cells: A multiphysics modeling approach

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