Steady saturation distribution in hydrophobic gas-diffusion layers of polymer electrolyte membrane fuel cells: A pore-network study

Lee, Kyu-Jin; Nam, Jin Hyun; Kim, Charn-Jung

doi:10.1016/j.jpowsour.2009.06.076

Cited by 65 publications

(71 citation statements)

References 39 publications

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“…However, using direct visualization in an operating fuel cell, Zhang et al 16 revealed that during operation the GDL/CL interface is covered with several independent water clusters. Lee et al 5 found that the maximum saturation at the GDL/CL interface can vary by 44% when comparing the uniform pressure to uniform flux boundary condition.…”

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confidence: 99%

Investigating Inlet Condition Effects on PEMFC GDL Liquid Water Transport through Pore Network Modeling

Fazeli

Hinebaugh

Bazylak

2015

J. Electrochem. Soc.

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In this work, the influence of the liquid water inlet boundary conditions at the gas diffusion layer (GDL)/catalyst layer interface on the spatial distribution of liquid water within the GDL was studied. We used pore network modeling with invasion percolation to simulate liquid water transport in a commercially available GDL, where the detailed, 3D microstructure of the GDL was obtained through X-ray imaging. Three inlet boundary conditions were studied: uniform pressure (single reservoir), uniform flux (completely discretized reservoirs), and distributed uniform pressure (random spatial-and size-distributions of reservoirs). We presented the distributed uniform pressure boundary condition as a more realistic inlet, where inlets are randomly distributed reservoirs that are connected to multiple inlet pores. It was found that the overall saturation ranged from 6% to 28% when the number of inlets ranged from 20 to 300; however, the GDL/catalyst layer delamination dominated water transport behavior. Proton exchange membrane fuel cells (PEMFCs) are promising electrochemical energy conversion devices; however, at high current densities they are prone to the accumulation of excess liquid water (flooding) in the cathode gas diffusion layer (GDL). This excess water leads to problems such as reduced oxygen transport pathways to the catalyst layer (CL), performance degradation, and reduced efficiency.Pore network modeling is a simulation tool for studying transport phenomena in porous media which is utilized here to investigate the steady state liquid water configurations in GDLs. A pore network model is a network diagram of pores (nodes) and throats (bonds) that represent a porous media, where pores are locations of large void spaces and throats are the local constrictions that connect adjacent pores. Several researchers have developed and applied pore network models to simulate the distribution of liquid water in the GDL. 1-11The introduction of water into the GDL occurs through a variety of mechanisms: electro-osmotic water transport across the membrane, water production from the oxygen reduction reaction, water vapor condensation within the bulk of the GDL, and condensation near the low temperature ribs of the flow field. The spatial distribution of liquid water and saturation (fraction of pore volume occupied by liquid water) within the bulk GDL depends on how liquid water is introduced to this porous layer, specifically at the interface between the GDL and the CL. However, the precise configuration of liquid water inlets at this interface is not well understood.Many authors have provided valuable insight into how inlet conditions heavily influence the spatial distribution of liquid water in the material. 2,4,5,[12][13][14][15] Two types of boundary conditions have been generally considered in isolation for studying liquid water transport in the GDL: uniform pressure boundary condition 2,15 and uniform flux boundary condition. 4 For the uniform pressure boundary condition, all inlet pores along the GDL/CL interface a...

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Investigating Inlet Condition Effects on PEMFC GDL Liquid Water Transport through Pore Network Modeling

Fazeli

Hinebaugh

Bazylak

2015

J. Electrochem. Soc.

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“…In the literature, there have been many pore-scale numerical studies of liquid water transport in the GDL ([2, [16][17][18] many thereof) and gas channels (GCs) [19]. Recently, evaporation was also included in the pore-network modeling [2,20] for understating its role in water management.…”

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confidence: 99%

Pore-Network Modeling of Water and Vapor Transport in the Micro Porous Layer and Gas Diffusion Layer of a Polymer Electrolyte Fuel Cell

2016

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Abstract:In the cathode side of a polymer electrolyte fuel cell (PEFC), a micro porous layer (MPL) added between the catalyst layer (CL) and the gas diffusion layer (GDL) plays an important role in water management. In this work, by using both quasi-static and dynamic pore-network models, water and vapor transport in the MPL and GDL has been investigated. We illustrated how the MPL improved water management in the cathode. Furthermore, it was found that dynamic liquid water transport in the GDL was very sensitive to the built-up thermal gradient along the through-plane direction. Thus, we may control water vapor condensation only along GDL-land interfaces by properly adjusting the GDL thermal conductivity. Our numerical results can provide guidelines for optimizing GDL pore structures for good water management.

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“…This has stimulated many pore-scale numerical studies of the GDL over the past few years. [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] Several distinctive features of liquid water transport in the GDL make its pore-scale modeling extremely difficult. First, a small flow rate of liquid water, with a capillary number value of around 10 −8 , causes the modeling computationally expensive.…”

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confidence: 99%

“…In such a way, the computational effort can be reduced considerably. There have been many invasionpercolation-based quasi-static pore network models used in the GDL studies, [15][16][17][18][19][20][21][22][23][24][25][26] which are very computationally cheap. These models are usually used to provide material properties like capillary pressure and relative permeability curves of the GDL, 15,16,22 which are required in the Darcy-scale modeling.…”

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“…2,35,36 Also, given the fact that liquid water transport in the GDL is strongly capillarity-dominant, the quasi-static z E-mail: chaozhong.qin@gmail.com; c.qin@uu.nl models are able to predict the flow pattern of liquid water. For example, Lee et al 25,26 developed a pore-network model combining invasion-percolation path finding and subsequent viscous two-phase flow calculation to investigate steady-state water distributions in the GDL. Although the model is computationally effective, it is worth noting that cyclic processes of local drainage and imbibition may prevail over the whole network; thus a steady-state viscous flow at the pore scale does not exist.…”

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Water Transport in the Gas Diffusion Layer of a Polymer Electrolyte Fuel Cell: Dynamic Pore-Network Modeling

Qin¹

2015

J. Electrochem. Soc.

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The pore-scale modeling is a powerful tool for increasing our understanding of water transport in the fibrous gas diffusion layer (GDL) of a polymer electrolyte fuel cell (PEFC). In this work, a new dynamic pore-network model for air-water flow in the GDL is developed. It incorporates water vapor transport coupled with liquid water by a phase change model. One important feature of our pore-network model is that a recently developed semi-implicit scheme for the update of water saturation is used. It provides good numerical stability in modeling liquid water transport in the GDL even for very small capillary number values. A number of case studies are conducted to illustrate several important mechanisms of water transport in the GDL, such as cyclic processes of local drainage and imbibition, channeling and capillary-fingering evolutions of water flow pattern, and eruptive water transport. Moreover, we show that liquid water separation in the GDL between the ribs and gas channel (GC) is formed under dry GC condition, which is qualitatively in agreement with in situ experimental results. Water management plays an important role in the durability and performance of polymer electrolyte fuel cells (PEFCs). A delicate water balance must be maintained to keep the membrane hydrated and at the same time avoid liquid water flooding in the porous components. [1][2][3] Over the past two decades, numerous studies have been conducted for improving our understanding of water transport mechanisms within the PEFC. Compared to the anode side, water transport in the cathode has usually attracted more attention. This is because the cathode is prone to being flooded first, and the oxygen reduction reaction (ORR) is very sluggish. The fibrous gas diffusion layer (GDL), as a key component, plays an important role in removing excessive water from the catalyst layer (CL) to the gas channel (GC). Up to now, much effort has been invested in gaining insights into pore-scale processes of liquid water transport in the GDL. [4][5][6][7][8][9][10] Despite the great success in in situ observations of water distribution, 8,9,[11][12][13][14] water dynamics in the GDL is still not well understood. Also, the cost of those experiments is quite high. This has stimulated many pore-scale numerical studies of the GDL over the past few years. [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] Several distinctive features of liquid water transport in the GDL make its pore-scale modeling extremely difficult. First, a small flow rate of liquid water, with a capillary number value of around 10 −8 , causes the modeling computationally expensive. Second, the complexity 34 of the pore structure and mixed wettability of the GDL give rise to the difficulty in developing an elegant pore-scale model. Nevertheless, many achievements still have been booked.Mukherjee et al. 4 were the first to conduct the Lattice-Boltzmann modeling of air-water flow in a stochastically reconstructed nonwoven GDL. The authors illustrated the structure-wettabili...

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Steady saturation distribution in hydrophobic gas-diffusion layers of polymer electrolyte membrane fuel cells: A pore-network study

Cited by 65 publications

References 39 publications

Investigating Inlet Condition Effects on PEMFC GDL Liquid Water Transport through Pore Network Modeling

Investigating Inlet Condition Effects on PEMFC GDL Liquid Water Transport through Pore Network Modeling

Pore-Network Modeling of Water and Vapor Transport in the Micro Porous Layer and Gas Diffusion Layer of a Polymer Electrolyte Fuel Cell

Water Transport in the Gas Diffusion Layer of a Polymer Electrolyte Fuel Cell: Dynamic Pore-Network Modeling

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