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.

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.

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.

In-Situ and Ex-Situ Investigation of Lateral Current Density Variations in a PEM Fuel Cell With Serpentine Flow Field

2009 ◽  
Author(s):  
Andrew Higier ◽  
Hongtan Liu
Keyword(s):  
Fuel Cell ◽  
Flow Field ◽  
Contact Resistance ◽  
Current Density ◽  
Pem Fuel Cell ◽  
Gas Diffusion ◽  
Operating Conditions ◽  
Ex Situ ◽  
Serpentine Flow Field

One of the most common types of flow field designs used in proton exchange membrane (PEM) fuel cell is the serpentine flow field. It is used for its simplicity of design, its effectiveness in distributing reactants and its water removal capabilities. The knowledge about where current density is higher, under the land or the channel, is critical for flow field design and optimization. Yet, no direct measurement data are available for serpentine flow fields. In this study a fuel cell with a single channel serpentine flow field is used to separately measure the current density under the land and channel on the cathode. In this manner, a systematic study is conducted under a wide variety of conditions and a series of comparisons are made between land and channel current density. Results show that under most operating conditions, current density is higher under the land than that under the channel. However, at low voltage, a rapid drop off in current density occurs under the land due to concentration losses. In order to investigate the cause of the variations of current density under the land and channel and series of ex-situ and in-situ experiments were conducted. In the ex-situ portion of the study, the contact resistance between the gas diffusion electrode (GDE) and the graphite flow plate were measured using an ex-situ impedance spectroscopy technique. The values of the contact resistance under the channel were found to be larger than that under the land. This implies that the contact resistance under the land and channel vary greatly, likely due to variations in compression under different section of the flow field. These variations in turn cause current density variations under the land and channel.

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.

Experimental Observation of Liquid Water Formation in Cathode Side Gas Channel of a Transparent PEM Fuel Cell

2006 ◽  
Author(s):  
Mingfei Gan ◽  
Lea Der Chen ◽  
P. C. Sui
Keyword(s):  
Fuel Cell ◽  
Experimental Observation ◽  
Liquid Water ◽  
Liquid Droplet ◽  
Proton Exchange ◽  
Operating Conditions ◽  
Cathode Side ◽  
Two Phase ◽  
Gas Channel ◽  
Water Formation

This paper reports on an experimental observation of water formation in a proton exchange membrane fuel cell (PEMFC). A fuel cell assembly with transparent end plates showing the gas channels is used. The study shows that liquid water can be present inside the gas channel of the fuel cell at a relatively low current density condition. The presence of liquid water could be in the form of mist-flow, suspended droplets, and sporadic liquid-gas two-phase flows, depending on operating conditions of the fuel cell. The voltage of the transparent fuel cell degraded over time, which is thought to be a result due to contamination from the fabrication of the gas channel plates of the transparent fuel cell. Onsets of the liquid droplet formation in gas channels are compared to the qualitative descriptions of homogeneous and heterogeneous nucleation theories.

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.

Predicting Liquid Water Saturation Through Differently Structured Cathode Gas Diffusion Media of a Proton Exchange Membrane Fuel Cell

2012 ◽  
Vol 9 (2) ◽  
Author(s):  
N. Akhtar ◽  
P. J. A. M. Kerkhof
Keyword(s):  
Fuel Cell ◽  
Liquid Water ◽  
Proton Exchange Membrane ◽  
Water Saturation ◽  
Catalyst Layer ◽  
Gas Diffusion ◽  
Proton Exchange ◽  
Diffusion Media ◽  
Exchange Membrane

The role of gas diffusion media with differently structured properties have been examined with emphasis on the liquid water saturation within the cathode of a proton exchange membrane fuel cell (PEMFC). The cathode electrode consists of a gas diffusion layer (GDL), a micro-porous layer and a catalyst layer (CL). The liquid water saturation profiles have been calculated for varying structural and physical properties, i.e., porosity, permeability, thickness and contact angle for each of these layers. It has been observed that each layer has its own role in determining the liquid water saturation within the CL. Among all the layers, the GDL is the most influential layer that governs the transport phenomena within the PEMFC cathode. Besides, the thickness of the CL also affects the liquid water saturation and it should be carefully controlled.

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