Liquid Water Transport and Distribution in Fibrous Porous Media and Gas Channels

2008 ◽  
Author(s):  
Dirk Rensink ◽  
Jo¨rg Roth ◽  
Stephan Fell
Keyword(s):  
Fuel Cell ◽  
Liquid Water ◽  
Catalyst Layer ◽  
Pem Fuel Cell ◽  
Pem Fuel Cells ◽  
Gas Diffusion ◽  
Operating Conditions ◽  
Cathode Side ◽  
Porous Layers ◽  
Micro Channels

In a polymer electrolyte membrane (PEM) fuel cell water is produced by electrochemical reactions in the catalyst layer on the cathode side. The water diffuses through the catalyst layer and a fibrous substrate into gas channels where it is transported away by convection. The fibrous substrate represents the gas diffusion media (GDM). Sometimes the GDM has a thin microporous layer on the side facing the catalyst layer. The same layer structure can be found on the anode side. All layers together are the porous layers of a PEM fuel cell. Under certain operating conditions condensation can occur in the porous layers which might lead to flooding conditions and — if the liquid water forms droplets which grow together in the gas channels — the complete blockage of the channels. Both situations can lead to a local starvation of reactant gases with negative impact on fuel cell performance and durability. The void space of the hydrophobic fibrous substrate in a PEM fuel cell can be interpreted as micro channels in a broader sense, especially if liquid phase transport from the catalyst layer towards the gas channels is in focus. Due to the small dimensions with effective channel diameter in the range of micrometer the flow of liquid water is governed by capillary forces. The same applies for the gas channels at low gas velocities since the Bond and Capillary numbers are well below one. Thus the investigation of liquid water flow and distribution under low gas velocities in the hydrophobic fibrous substrate and the spreading of liquid water along the hydrophilic gas channel walls under capillary action is of special interest for PEM fuel cells and investigated here.

Experimental Investigation of Liquid Water Formation and Transport in a Transparent Single-Serpentine PEM Fuel Cell

2006 ◽  
Author(s):  
Dusan Spernjak ◽  
Suresh Advani ◽  
Ajay K. Prasad
Keyword(s):  
Fuel Cell ◽  
Flow Field ◽  
Liquid Water ◽  
Catalyst Layer ◽  
Pem Fuel Cell ◽  
Gas Diffusion ◽  
Operating Conditions ◽  
Cathode Side ◽  
Water Formation ◽  
Transparent Cell

Liquid water formation and transport was investigated by direct experimental visualization in an operational transparent single-serpentine PEM fuel cell. We examined the effectiveness of various gas diffusion layer (GDL) materials in removing water away from the cathode and through the flow field over a range of operating conditions. Complete polarization curves as well as time evolution studies after step changes in current draw were obtained with simultaneous liquid water visualization within the transparent cell. At similar current density (i.e. water production rate), lower level of cathode flow field flooding indicated that liquid water had been trapped inside the GDL pores and catalyst layer, resulting in lower output voltage. No liquid water was observed in the anode flow field unless cathode GDLs had a microporous layer (MPL). MPL on the cathode side creates a pressure barrier for water produced at the catalyst layer. Water is pushed across the membrane to the anode side, resulting in anode flow field flooding close to the H2 exit.

scholarly journals A Kernel for Calculating PEM Fuel Cell Distribution of Relaxation Times

2021 ◽  
Vol 9 ◽  
Author(s):  
Andrei Kulikovsky
Keyword(s):  
Fuel Cell ◽  
Oxygen Transport ◽  
Relaxation Times ◽  
Catalyst Layer ◽  
Pem Fuel Cell ◽  
Negative Real Part ◽  
Gas Diffusion ◽  
Transport Processes ◽  
Transport Layer ◽  
Cathode Side

Impedance of all oxygen transport processes in PEM fuel cell has negative real part in some frequency domain. A kernel for calculation of distribution of relaxation times (DRT) of a PEM fuel cell is suggested. The kernel is designed for capturing impedance with negative real part and it stems from the equation for impedance of oxygen transport through the gas-diffusion transport layer (doi:10.1149/2.0911509jes). Using recent analytical solution for the cell impedance, it is shown that DRT calculated with the novel K2 kernel correctly captures the GDL transport peak, whereas the classic DRT based on the RC-circuit (Debye) kernel misses this peak. Using K2 kernel, analysis of DRT spectra of a real PEMFC is performed. The leftmost on the frequency scale DRT peak represents oxygen transport in the channel, and the rightmost peak is due to proton transport in the cathode catalyst layer. The second, third, and fourth peaks exhibit oxygen transport in the GDL, faradaic reactions on the cathode side, and oxygen transport in the catalyst layer, respectively.

A Lumped Model of Single Droplet Deformation, Oscillation and Detachment on the GDL Surface of a PEM Fuel Cell

2010 ◽  
Author(s):  
Angelo Esposito ◽  
Pierpaolo Polverino ◽  
Cesare Pianese ◽  
Yann G. Guezennec
Keyword(s):  
Fuel Cell ◽  
Liquid Water ◽  
Gas Diffusion ◽  
Proton Exchange ◽  
Operating Conditions ◽  
Force Balance ◽  
Mass Motion ◽  
Gas Velocity ◽  
Droplet Shape ◽  
Micro Channels

Proton Exchange Membrane Fuel Cell performance significantly depends on electrode water content. Indeed, an excess of liquid water in the pores of the gas diffusion layer (GDL) and in the gas flow channel (GFC) can drastically bring down the output power. Depending on the operating conditions, liquid water emerging from the GDL micro-channels can form droplets, films or slugs in the GFC. In the regime of droplets formation, the interaction with the gas crossing-flow leads to an oscillating mechanisms that is fundamental to studying the detachment from the GDL surface, as the authors have shown in a previous publication. In this work, a numerical model of a droplet growing on the GDL surface is developed to describe the interaction between droplet cross-flowing gas stream. The droplet shape and its deformation are reconstructed assuming a known geometry. Therefore, a lumped force balance is enforced to determine the center of mass motion law. Oscillation frequencies during growth and at detachment are found as a function of droplet size. The model is also exploited to find the relationship between droplet critical detachment size and gas velocity. The numerical results are compared with the droplet frequency-size and detachment size-gas velocity experimental results previously presented by the authors. The matching between the numerical and experimental data is very good and is a mean of validation for the model. The low computational burden and the conciseness of the results make the model suitable for applications such as control and optimization strategies development to enhance PEMFC performance. Additionally, the model can be exploited to implement monitoring and diagnostic algorithm.

Simulation-Aided PEM Fuel Cell Design and Performance Evaluation

2004 ◽  
Vol 2 (1) ◽  
pp. 20-28 ◽  
Author(s):  
Junxiao Wu ◽  
Qingyun Liu
Keyword(s):  
Fuel Cell ◽  
Catalyst Layer ◽  
Pem Fuel Cells ◽  
Gas Diffusion ◽  
Operating Conditions ◽  
Half Cell ◽  
Flow Channels ◽  
Simulation Strategy ◽  
Cell Simulation ◽  
And Performance

A multi-resolution fuel cell simulation strategy has been employed to simulate and evaluate the design and performance of hydrogen PEM fuel cells with different flow channels. A full 3D model is employed for the gas diffusion layer and a 1D+2D model is applied to the catalyst layer. Further, a quasi-1D method is used to model the flow channels. The cathode half-cell simulation was performed for three types of flow channels: serpentine, parallel, and interdigitated. Simulations utilized the same overall operating conditions. Comparisons of results indicate that the interdigitated flow channel is the optimal design under the specified operating conditions.

Cold Pre-Compression Treatment of Gas Diffusion Electrode for PEM Fuel Cells

2011 ◽  
Author(s):  
Shan Jia ◽  
Hongtan Liu
Keyword(s):  
Fuel Cell ◽  
Pem Fuel Cell ◽  
Pem Fuel Cells ◽  
Gas Diffusion ◽  
Gas Diffusion Electrode ◽  
Operating Conditions ◽  
Cell Performance ◽  
Experimental Results ◽  
Overall Performance ◽  
Compression Treatment

In a PEM fuel cell, it has been shown that the compression under the land area is the main reason for the observed higher performance than that under channel areas. If the area under the channel can also benefit from such a compression the overall performance of the cell will increase. Since the areas under the channel are not directly compressed in an assembled fuel cell, it is the objective of this study to determine if a cold pre-compression treatment of the gas diffusion electrode (GDE) may have a significant positive effect on the overall performance of the cell. First, the GDE is cold pre-compressed to a level similar to the compression that would be experienced by the land areas in an assembled fuel cell. Then the pre-compressed GDE is assembled in a regular test fuel cell and the performances under various operating conditions are studied. Finally, the cell performance results are compared with the results obtained from a fuel cell with a regular GDE. The experimental results show that cold pre-compress of the GDE has significantly improved the overall performance of the fuel cell. Further experiments have also been conducted with five different levels of cold pre-compression to determine if there exists an optimal compression and its value if it exists. The experimental results show that the performance of the fuel cell first increases with the level of cold pre-compression, reaching a maximum and then decreases with the level of compression. These results clearly indicate that there indeed exists an optimal level of compression. Further studies using both cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) have further corroborated the cell performance findings as well as the underlying mechanism. The results of EIS indicate that the ohmic resistance is hardly affected by the cold pre-compression, while the charge transfer resistance is significantly affected, especially in high current density region. The CV results show that the electro-chemical area (ECA) is higher with the cold pre-compressed GDE and there is an optimal compression that results in the maximum ECA. Therefore, the experimental results have shown that (a) the cold pre-compression treatment of the GDE is an effective and simple technique to increase PEM fuel cell performances; (b) there exists an optimal compression level at which the cell reaches its maximum performance; and (c) the increased performance is due to the increase of ECA resulting from the cold pre-compression treatment.

Development of a PEM Fuel Cell Electrode Coating Testbed

2010 ◽  
Author(s):  
Casey J. Hoffman ◽  
Daniel F. Walczyk
Keyword(s):  
Fuel Cell ◽  
Large Scale ◽  
Platinum Catalyst ◽  
Polymer Electrolyte Membrane ◽  
Quality Measurement ◽  
Catalyst Layer ◽  
Pem Fuel Cell ◽  
Pem Fuel Cells ◽  
Gas Diffusion ◽  
Electrode Coating

Two of the largest barriers to PEMFC commercialization are the materials costs for individual components, especially platinum catalyst, and the fact that few large-scale manufacturing capabilities currently exist. This paper focuses on the development of a testbed which will be used for evaluating coating technologies for use in the manufacture of polymer electrolyte membrane (PEM) fuel cell electrodes. More specifically, the focus is on diffusion electrode architecture, in which the catalyst layer is applied to a gas diffusion layer (GDL) rather than on the membrane. These electrodes are used for both low- and high-temperature PEM fuel cells. A flexible web coating testbed has been designed and built to allow for testing of different gas diffusion electrode (GDE) and GDL deposition methods. This testbed, which is approximately two meters in length, includes a variety of both coating and drying capabilities as well as additional space for quality measurement and control system testing. Testbed capabilities and planned experimentation is discussed in detail. In the future, various non-contact deposition methods for the microlayer and catalyst inks will be investigated (e.g., direct spray, ultrasonic spray) to determine those that will provide higher throughput and repeatability through increased process control capability, while improving electrode performance.

The Effect of Variable Catalyst Loading in Electrodes on PEM Fuel Cell Performance

2005 ◽  
Author(s):  
R. Roshandel ◽  
B. Farhanieh
Keyword(s):  
Fuel Cell ◽  
Current Density ◽  
Catalyst Layer ◽  
Pem Fuel Cell ◽  
Pem Fuel Cells ◽  
Cell Performance ◽  
Cathode Side ◽  
Catalyst Loading ◽  
Fuel Cell Performance ◽  
Reactant Concentration

Catalyst layers are one the important parts of the PEM fuel cells as they are the main place for electrochemical reaction taking place in anode and cathode of the cells. The amount of catalyst loading of this layer has a large effect on PEM fuel cell performance. Non-uniformity of reactant concentration could lead to a variation of current density in anode and cathode catalyst layer. The main reason for this phenomenon is porosity variation due to two effects: 1. compression of electrode on the solid landing area and 2. Water produced at the cathode side of diffusion layer. In this study the effect of variable current density in anode and cathode electrode on cell performance is investigated. It has shown that better cell performance could be achieved by adding a certain amount of catalyst loading to each electrode, with respect to the reactant concentration.

Effect of Porosity Gradient in Gas Diffusion Layer on Cell Performance With Thin-Film Agglomerate Model in Cathode Catalyst Layer of a PEM Fuel Cell

2011 ◽  
Author(s):  
Chun-I Lee ◽  
Shiqah-Ping Jung ◽  
Kan-Lin Hsueh ◽  
Chi-Chang Chen ◽  
Wen-Chen Chang
Keyword(s):  
Thin Film ◽  
Fuel Cell ◽  
Diffusion Layer ◽  
Liquid Water ◽  
Water Saturation ◽  
Catalyst Layer ◽  
Gas Diffusion Layer ◽  
Pem Fuel Cell ◽  
Gas Diffusion ◽  
Water Flooding

A one-dimensional, steady-state, two-phase, isothermal numerical simulations were performed to investigate the effect on cell performance of a PEM fuel cell under non-uniform porosity of gas diffusion layer. In the simulation, the non-uniform porosity of gas diffusion layer was taken into account to analyze the transport phenomena of water flooding and mass transport in the gas diffusion layer. The porosity of the gas diffusion layer is treated as a linear function. Furthermore, the structure of the catalyst layer is considered to be a cylindrical thin-film agglomerate. Regarding the distribution analysis of liquid water saturation, oxygen concentration and water concentration depend on the porosity of gas diffusion layer. In the simulation, the εCG and εGC represent the porosity of the interfaces between the channel and gas diffusion layer and the gas diffusion layer and the catalyst layer, respectively. The simulation results indicate that when the (εCG, εGC) = (0.8, 0.4), higher liquid water saturation appears in the gas diffusion layer and the catalyst layer. On the contrary, when the (εCG, εGC) = (0.4, 0.4), lower liquid water saturation appears. Once the liquid water produced by the electrochemical reaction and condensate of vapor water may accumulate in the open pores of the gas diffusion layer and reduced the oxygen transport to the catalyst sites. This research attempts to use a thin-film agglomerate model, which analyze the significant transport phenomena of water flooding and mass transport under linear porosity gradient of gas diffusion layer in the cathode of a PEM fuel cell.

scholarly journals Numerical Analysis of Water Transport Through the Membrane Electrolyte Assembly of a Polymer Exchange Membrane Fuel Cell

2010 ◽  
Vol 7 (2) ◽  
Author(s):  
Xu Zhang ◽  
Datong Song ◽  
Qianpu Wang ◽  
Cheng Huang ◽  
Zhong-Sheng Liu ◽  
...  
Keyword(s):  
Fuel Cell ◽  
Water Transport ◽  
Liquid Water ◽  
Water Saturation ◽  
Gas Diffusion ◽  
Operating Conditions ◽  
Phase Changes ◽  
Cell Performance ◽  
Cathode Side ◽  
Exchange Membrane

The effects of water transport through membrane electrolyte assembly of a polymer exchange membrane fuel cell on cell performance has been studied by a one-dimensional, nonisothermal, steady-state model. Three forms of water are considered in the model: dissolved water in the electrolyte or membrane, and liquid water and water vapor in the void space. Phase changes among these three forms of water are included based on the corresponding local equilibriums between the two involved forms. Water transport and its effect on cell performance have been discussed under different operating conditions by using the value and the sign of the net water transport coefficient, which is defined by the net flux of water transported from the anode side to the cathode side per proton flux. Optimal cell performance can be obtained by adjusting the liquid water saturation at the interface of the cathode gas diffusion layer and flow channels.

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