Study on Water Transport Phenomena Through Micro-Porous Layers in PEFC

2012 ◽  
Author(s):  
Takemi Chikahisa ◽  
Yutaka Tabe ◽  
Kazumasa Kadowaki
Keyword(s):  
Water Transport ◽  
Water Distribution ◽  
Produced Water ◽  
Catalyst Layer ◽  
Operating Conditions ◽  
Water Flooding ◽  
Cathode Side ◽  
Porous Layers ◽  
Condensed Water ◽  
Vapor Pressure Gradient

Micro-porous layers (MPLs) play an important role in the water management of polymer electrolyte fuel cells (PEFCs), but details of the mechanism that works to suppress water flooding has not been fully understood. In this study, the authors investigated water distribution at the interface between the MPL and the catalyst layer (CL) at the cathode side to clarify the effect of the MPL on the discharge of produced water. A freezing method was applied to observe the distribution of the condensed water, and the ice distribution on the CL surface was quantified by image processing. The effects of operating conditions on the water distribution were examined at normal temperature conditions. The distribution of ice formed on the surface of the CL with and without MPL after −10°C cold start operation was also established. Water transport rate in the vapor phase was analyzed based on temperature and vapor pressure gradient considerations. The experiments and the analysis showed that the MPL functions to prevent accumulation of water on the surface of the CL, resulting in less water flooding.

Analysis of Water Transport in the Vicinity of Micro-Porous Layer in PEFC With Freezing Method

2013 ◽  
Author(s):  
Yusuke Aoyama ◽  
Kengo Suzuki ◽  
Yutaka Tabe ◽  
Takemi Chikahisa
Keyword(s):  
Catalyst Layer ◽  
Cathode Side ◽  
Cross Sectional ◽  
Porous Layers ◽  
Freezing Method ◽  
Water Condensation ◽  
Flow Channels ◽  
Condensed Water ◽  
Electronic Microscope

This paper examines the role of micro porous layers (MPLs) in Polymer Electrode Fuel Cells (PEFCs) by observing the cross-sectional distribution of condensed water inside a cathode side MPL In addition, the forms of water condensation in the vicinity of a MPL are also compared between two places, under flow channels and under lands, by observing both inside the MPL and an interface between the MPL and a catalyst layer (CL). The freezing method and a cryo-scanning electronic microscope (cryo-SEM) are used for the observation. The result under the non-flooded condition shows that condensed water does not accumulate inside the MPL. This result indicates that the water produced by PEFC power generation passes through the MPL as vapor state under non-flooded conditions.

In-Situ Observation of the Water Distribution in Porous Layers of PEMFCs by Soft X-Ray Radiography

2010 ◽  
Author(s):  
Takashi Sasabe ◽  
Shohji Tsushima ◽  
Shuichiro Hirai
Keyword(s):  
Water Transport ◽  
Temporal Resolution ◽  
Liquid Water ◽  
Water Distribution ◽  
Transport Phenomena ◽  
Catalyst Layer ◽  
In Situ Observation ◽  
X Ray ◽  
Porous Layers ◽  
Liquid Water Transport

To observe the liquid water distribution in porous layers of an operational Proton Exchange Membrane Fuel Cell (PEMFC) with high spatial and temporal resolution, Laboratory-based soft X-ray microscopy has developed. This system can generate low energy X-ray in the soft X-ray range, and maximum sensitivity towards water is achieved. A point X-ray source with a diameter of less than 1.0 μm and the improved detector optics contribute to realize a spatial resolution of 500 nm and a temporal resolution of 1.0 sec/frame. In addition, in-plane and through-plane observations of an operational PEMFC were carried out. In the in-plane observation test, non-uniform distribution of liquid water in the plane of the catalyst layer was observed, and the importance of appropriate design of the catalyst layer to liquid water transport phenomena was suggested. In the through-plane observation test, liquid water discharge behavior near under the rib area was observed, and the importance of channel wall wettability to liquid water transport phenomena was also suggested.

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.

Effect of Operating Conditions on the Water Transport Phenomena at the Cathode of Polymer Electrolyte Membrane Fuel Cell

2009 ◽  
Author(s):  
Sang Hern Seo ◽  
Chang Sik Lee
Keyword(s):  
Fuel Cell ◽  
Polymer Electrolyte ◽  
Water Transport ◽  
Flow Rate ◽  
Water Droplet ◽  
Polymer Electrolyte Membrane ◽  
Transport Phenomena ◽  
Operating Conditions ◽  
Water Flooding ◽  
Electrolyte Membrane

Water management is very important for polymer electrolyte membrane fuel cell because the fuel cell performance is decreased by flooding phenomena generated by liquid water in the cathode channels. In addition, the proton conductivity and water transport of membrane could become different by hydration contents of membrane. This study is observed water transport phenomena of cathode channels with a polymer electrolyte membrane fuel cell according to various operating conditions. In order to obtain the water images, the transparent fuel cell consists of polycarbonate window of the cathode end plate and gold coated stainless steel as the flow field and current collector of the cathode. To investigate the effects of operating conditions on the water transport, experiments were conducted under various operating conditions such as cell temperature, cathode flow rate and cathode backpressure. As operating time elapsed, it is observed that the water droplet formation, growth, coalescence and removal occurred in the cathode channel. It can be known that the high cathode flow rate prevents water flooding by removal of water in the cathode flow channel. Also, the quantity of water droplet was increased by the high cathode backpressure.

Visualization Study of Cathode Flooding With Different Operating Conditions in a PEM Unit Fuel Cell

2005 ◽  
Author(s):  
Han-Sang Kim ◽  
Tae-Hun Ha ◽  
Sung-Jin Park ◽  
Kyoungdoug Min ◽  
Minsoo Kim
Keyword(s):  
Fuel Cell ◽  
Water Transport ◽  
Proton Exchange Membrane ◽  
Ccd Camera ◽  
Proton Exchange ◽  
Operating Conditions ◽  
Cathode Side ◽  
Two Phase ◽  
Fuel Cell Performance ◽  
Study Results

Visualization technique was used to better understand the water build-up phenomena on the cathode side of a proton exchange membrane (PEM) unit fuel cell. In this study, a transparent PEM unit fuel cell with an active area of 25 cm2 was designed and fabricated to allow for the visualization of cathode channel with fuel cell performance characteristics. Two-phase flow due to the electrochemical reaction of fuel cell was experimentally investigated. The images photographed by CCD camera with various cell temperatures (30–50°C) and different inlet humidification levels were presented in this study. Results indicated that the flooding on the cathode side first occurs near the exit of cathode flow channel. As the fuel cell operating temperature increases, it was found that water droplets tend to evaporate easily because of increased saturation vapor pressure and it can have an influence on lowering the flooding level. The approaches of this study can effectively contribute to the detailed researches on water transport phenomena including modeling water transport of an operating PEM fuel cell.

Modeling of Liquid Water Transport in Cathode Catalyst Layer of PEM Fuel Cells

2009 ◽  
Author(s):  
Prodip K. Das ◽  
Xianguo Li ◽  
Zhong-Sheng Liu
Keyword(s):  
Water Transport ◽  
Liquid Water ◽  
Catalyst Layer ◽  
Pem Fuel Cells ◽  
Water Flooding ◽  
Dimensionless Time ◽  
Cathode Catalyst ◽  
Water Production ◽  
Cathode Catalyst Layer ◽  
Liquid Water Transport

The performance of a polymer electrolyte membrane (PEM) fuel cell is significantly affected by liquid water generated at the cathode catalyst layer (CCL). Conversely, the ionic conductivity of PEM is directly proportional to its water content; it must have sufficient water. Therefore, it is essential to maintain a delicate water balance, which seems difficult without properly understanding liquid water transport from the CCL. In the present study, a one-dimensional analytical solution of liquid water transport across the CCL is derived from the fundamental transport equations. The effect of CCL wettability on liquid water transport and the effect of liquid water “flooding” on reactant transport have been investigated. It has been observed that hydrophilic characteristic of a CCL plays significant role on the liquid water transport. The liquid water saturation in a hydrophilic CCL can be reduced by increasing the surface wettability or lowering contact angle. Based on a dimensionless time constants analysis, it has been shown that liquid water production from the phase change process is negligible compared to water production from the electrochemical process.

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.

Parametric Estimation of Heat and Water Management Strategy Preventing Condensed Water Formation in Polymer Electrolyte Fuel Cells

2008 ◽  
Author(s):  
Hye-Mi Jung ◽  
Kwan-Soo Lee ◽  
Sukkee Um
Keyword(s):  
Water Management ◽  
Fuel Cells ◽  
Polymer Electrolyte ◽  
Water Transport ◽  
Management Strategy ◽  
Produced Water ◽  
Polymer Electrolyte Fuel Cells ◽  
Water Formation ◽  
Condensed Water ◽  
Water Management Strategy

This work presents the comprehensive theoretical and numerical modeling efforts on the water transport phenomena in polymer electrolyte fuel cells and intends to elucidate an optimal water management strategy preventing condensed water formation in the anode and cathode channels. For a particular design of polymer electrolyte fuel cells, theoretical and numerical analyses on the inlet feed streams were conducted to set an optimal water transport strategy. The results showed that the favorable water transport scenario (half of produced water transported back to anode) requires less humidification at the gas channel inlets compared to the worst scenario (10% of the produced water diffused back to anode). It was also shown that for 80°C operation of fuel cells, the reactants should be super-saturated and the coolant temperature difference less than 5°C between the inlet and outlet has a significant effect on the humidification of reactant gases. For an optimal system, the inlet feed stream temperature and the temperature difference of the coolant should be carefully determined, considering the humidification capacity and the size of the radiator.

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.

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