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

Abstract

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...

Liquid water in cathode gas diffusion layers of PEM fuel cells: Identification of various pore filling regimes from pore network simulations

“…This has motivated quite a few studies using various techniques, such as Lattice Boltzmann Method, e.g. [11], or pore network models (PNM) [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29]. More classical continuum approaches based on the standard twophase flow model for porous media have been also used, e.g.…”

“…The first group is by far the largest in number of articles, e.g. [12][13][14][15][16][17][18][19][20][21][22][23]. The main assumption for this group is that water enters the GDL in liquid phase from the CL or MPL /GDL interface.…”

Comparison of Electrospun Carbon−Carbon Composite and Commercial Felt for Their Activity and Electrolyte Utilization in Vanadium Redox Flow Batteries

“…The single phase effective diffusion coefficients were calculated for both air and water (representative of the electrolyte) using Fick's law of diffusion. An invasion percolation algorithm developed by Hinebaugh et al ,. was used to investigate the electrolyte invasion behavior of the electrolyte into the electrode.…”

“…The pore network determines the morphology as a network of pores and throats where the pores act as reservoirs and the connecting throats define the transport pathways. Several groups have worked with pore network models in defining the transport through porous materials, in applications varying from fuel cell diffusion media,, PEM electrolyzers, redox flow battery electrodes, and rock structures . Banerjee et al .…”

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

“…This is probably because the boundary condition of pressure head was used in their experiment. In our work, the water flux boundary condition was used [2,29]. Furthermore, it was found that cracks in the MPL could reduce water flooding in the GDL significantly.…”