Progress in In Situ X-Ray Tomographic Microscopy of Liquid Water in Gas Diffusion Layers of PEFC

Eller, Jens; Rosén, Tomas; Marone, Federica; Stampanoni, Marco; Wokaun, Alexander; Büchi, Félix N.

doi:10.1149/1.3596556

Cited by 156 publications

(171 citation statements)

References 42 publications

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“…At least a two-channel design is required to obtain saturation and water distribution data over a channel & rib repetition unit without boundary bias, as it is the case in a single channel cell (Eller et al 28 ). Two different flow field designs, differing only in the rib width (0.8 and 1.6 mm) were used (see Figure 2).…”

Section: Methodsmentioning

confidence: 99%

“…Therefore, and different to Ref. 28, the dry XTM dataset were filtered with an inhouse implementation of the local normalization filter 38 which allows to remove the inhomogeneous background intensity within the GDL domain. The filter was applied in 2D for the in-plane (IP) direction to remove the CL patterns and in through-plane direction to remove the gradient of the gray levels from the CL toward the flow field.…”

Section: Xtm Imaging and Data Processingmentioning

confidence: 99%

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Operando Properties of Gas Diffusion Layers: Saturation and Liquid Permeability

Eller

Roth

Marone

et al. 2016

J. Electrochem. Soc.

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Polymer electrolyte fuel cells (PEFC) require a sophisticated water management to operate efficiently, especially at high current densities which are needed to reach system cost targets. The description of the complicated two-phase water transport remains a challenge in PEFC models and requires experimental validation on various length scales. In this work, operando X-ray tomographic microscopy (XTM) with scan times of 10 s was used to depict the liquid water at defined conditions at a technically relevant cell temperature of 80 • C. Cells with Toray TGP-H-060 gas diffusion layer (GDL) with microporous layer (MPL) and different rib width were operated with different feed gas humidifications (under-and oversaturated) and current densities between 0.75 to 3.0 A/cm 2 . Based on the quantification of the local and average saturation, the distribution of water cluster size is analyzed. Different categories of the water cluster connectivity are defined and quantified. The analysis is complemented with numerical simulations of the permeability in the liquid phase of the GDL that is correlated to saturation for the different GDL domains. The numerical simulations of the pressure drop of liquid water flow from the catalyst layer toward the gas channels in channel-rib repetition units allows for conclusions on cluster growth mechanisms. In the past two decades, large developments have lead hydrogen fed polymer electrolyte fuel cell (PEFC) technology to the brink of commercialization, e.g. in the stationary sector with more than 100000 deployments in the Enefarm activity 1 as well as in the mobile sector where major car manufacturers have presented first commercial vehicles 2,3 and niche-market commercialization for logistic vehicles. 4While for the automotive market also hydrogen infrastructure is a major barrier for widespread application, in both fields of application, cost of the fuel cell system remains the main hindrance for extensive spread of PEFC technology. Cost is closely tied to materials and manufacturing processes, such as more effective electrocatalyst and more durable membrane materials. These developments are underway and have made significant progress. 5 Cost however is also closely tied to power density of the fuel cell stack. It is obvious that with higher power density less cells or an accordingly smaller cell area with the related reduced material use, is leading to a cost reduction if the high power density materials are of comparable cost.Automotive fuel cells with state of the art materials and cell structures reach today more than 1 W/cm 2 with current densities up to 3 A/cm 2 .5 At such high current densities water management becomes more and more important and has to be properly designed on various scales from the system level to nanoscale structures, including all cell components as flow field plates, gas diffusion layers (GDL), the polymer membrane and the catalyst layer (CL). In order to minimize the ohmic losses, the polymer membrane needs to be well humidified, 6 however at high current den...

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Section: Methodsmentioning

confidence: 99%

Section: Xtm Imaging and Data Processingmentioning

confidence: 99%

Operando Properties of Gas Diffusion Layers: Saturation and Liquid Permeability

Eller

Roth

Marone

et al. 2016

J. Electrochem. Soc.

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“…[43][44][45][46][47][48]51,56,61,62,[64][65][66][67]71 Using XCT for membrane analysis is more challegning given the relatively low X-ray attenuation of the polymer. Garzon et al 68 demonstrated that Pt redistribution from the electrodes into the membrane can be captured by XCT.…”

mentioning

confidence: 99%

3D Failure Analysis of Pure Mechanical and Pure Chemical Degradation in Fuel Cell Membranes

Singh

Orfino

Dutta

et al. 2017

J. Electrochem. Soc.

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Lifetime-limiting failure of fuel cell membranes is generally attributed to their chemical and/or mechanical degradation. Although both of these degradation modes occur concurrently during operational duty cycles, their uncoupled investigations can provide useful insights into their individual characteristics and consequential impacts on the overall membrane failure. X-ray computed tomography is emerging as an advantageous tool for fuel cell failure analysis due to its non-destructive and non-invasive 3D imaging capabilities at ambient conditions. In the present work, post-mortem failure analysis of pure mechanical and pure chemical membrane degradation modes is performed three-dimensionally using this technique. A uniquely comprehensive analysis afforded by this technique reveals that membrane failure is almost exclusively characterized by crack formations during mechanical degradation and by severe thinning accompanied by electrode shorting and pinhole formation during chemical degradation, respectively. Catalyst layer cracks, particularly on the cathode side, are found to interact strongly with mechanically induced membrane cracks. The conjoint effect of chemical and mechanical stressors is established as a necessary requirement for: (i) exclusive membrane crack development independent of catalyst layer cracks; and (ii) crack branching during membrane crack propagation. Overall, the membrane failure analysis improves its reliability and quantitative character with the adoption of 3D imaging. The transportation sector is a significant contributor to global greenhouse gas emissions and with ever-growing concerns around the global warming effect, research and development of novel clean energy based automotive solutions is being pursued worldwide. Hydrogen fuel cells have thus far emerged as a promising alternative to fossil fuel based internal combustion engines due to their clean, noisefree, and efficient operation.1 Polymer electrolyte membrane (PEM) fuel cells 2 are widely used in fuel cell electric vehicles (FCEVs) and supply electrical energy from the electrochemical conversion of hydrogen and oxygen (usually supplied as air) into water. In automotive applications, the fluctuating operating conditions due to vehicle dynamics, variations in loads and environmental conditions, startups and shutdowns, fuel starvation, contamination, and freeze-thaw cycles pose significant durability challenges for the PEM fuel cells. 3Understanding the specific durability problems and developing suitable solutions remains a key research focus in automotive PEM fuel cell technology research and is critical to the long-term and large-scale commercial adoption of this technology. Given the complex interplay of multiple physical phenomena that are simultaneously active in an operating PEM fuel cell, various deleterious factors affecting PEM fuel cell components can collectively lead to a gradual performance loss and eventual failure.In PEM fuel cells, the electrodes are separated by a polymeric membrane which allows selective tran...

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“…As the hydrostatic pressure of water increases the water will penetrate into the pores of the GDL. Previous analyses of water penetration have generally assumed uniform pores in the GDL with complex connectivity [20][21][22][23][24]. Figure 10 presents an alternative type of pore structure where the pores have variable diameters along their length.…”

Section: Water Penetration Through the Gdlmentioning

confidence: 99%

“…They suggested that liquid water only penetrates a few large pores and the smaller pores, that comprise the majority of the pore volume, remain free of liquid water and allow gas to be transported from the gas flow channel to the catalyst layer. Other researchers have employed NMR and neutron scattering imaging to confirm that liquid water penetrates only the largest pores [22][23][24]. The incipient water penetration results indicate that the tail of the pore size distribution is critical for controlling water transport.…”

Section: Introductionmentioning

confidence: 99%

Water Flow in, Through, and Around the Gas Diffusion Layer

et al. 2012

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Liquid water produced in polymer electrolyte membrane fuel cells is transported from the cathode catalyst/membrane interface through the gas diffusion layer (GDL) to the gas flow channel. Liquid water travels both laterally (in the plane of GDL) and transversely through the largest pores of the porous GDL structure. Narrow apertures in the largest pores are the primary resistance to liquid water penetration. Carbon paper has limiting apertures ∼20 μm in diameter and ∼1 μm in length whereas carbon cloth has apertures ∼100 μm in diameter and ∼200 μm in length. After sufficient hydrostatic pressure is applied, water penetrates the limiting aperture and flows through the pore. The pressure required for water to flow through the pores is less than the pressure to penetrate the limiting aperture of the pores. Water moved laterally and directed through a small number of transverse pores. There is less resistance to lateral liquid water flow at the interface between the GDL and a solid surface than through the GDL. The results from these experiments suggest that water flow through the GDL is dominated by a small number of pores and most pores remain free of liquid water.

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Progress in In Situ X-Ray Tomographic Microscopy of Liquid Water in Gas Diffusion Layers of PEFC

Cited by 156 publications

References 42 publications

Operando Properties of Gas Diffusion Layers: Saturation and Liquid Permeability

Operando Properties of Gas Diffusion Layers: Saturation and Liquid Permeability

3D Failure Analysis of Pure Mechanical and Pure Chemical Degradation in Fuel Cell Membranes

Water Flow in, Through, and Around the Gas Diffusion Layer

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