Neutron Imaging of Water Accumulation in the Active Area and Channel-to-Manifold Transitions of a PEMFC

2013 ◽  
Author(s):  
Xuan Liu ◽  
Thomas A. Trabold ◽  
Jeffrey J. Gagliardo ◽  
David L. Jacobson ◽  
Daniel S. Hussey
Keyword(s):  
Fuel Cell ◽  
Current Density ◽  
Liquid Water ◽  
Driving Force ◽  
Cell Voltage ◽  
Neutron Imaging ◽  
Active Area ◽  
Water Volume ◽  
Imaging Method ◽  
Water Accumulation

Management of liquid water formed by the electrochemical fuel cell reaction is a key factor in PEMFC performance and durability. For practical stack applications, an important consideration is the transport of liquid water at the transition between the ends of the bipolar plate channels and the manifolds, where excess reactant flows from all the individual cells are combined and directed to the stack exhaust. In this region, gas-phase momentum can be very low, especially on the anode, where there is little driving force to remove liquid water that may accumulate as a result of geometrical or surface energy variations, or due to relatively low temperatures that exist outside of the fuel cell active area. This study seeks to characterize the water accumulated within the active area and at the channel-to-manifold transition regions at both the anode and cathode outlets, as a function of cell operating temperature and current density. The neutron imaging method was applied to directly measure the water volumes within the transition regions, and provide a comparison to simultaneously measured water volume within the cell active area. Transition-region water was found to be weakly dependent on current density, suggesting that once water forms in this area, little driving force exists to extract it entirely by means of gas momentum. Moreover, it was found that the active area water volume is strongly dependent on cell temperature, and temperature variation of as little as 0.5 °C can produce a significant change in water accumulation which is reflected in the cell voltage.

Analysis of Water Morphology in the Active Area and Channel-to-Manifold Transitions of a PEM Fuel Cell

2014 ◽  
Author(s):  
Daniel J. Fenton ◽  
Jeffrey J. Gagliardo ◽  
Thomas A. Trabold
Keyword(s):  
Fuel Cells ◽  
Fuel Cell ◽  
Flow Field ◽  
Current Density ◽  
Liquid Water ◽  
Pem Fuel Cells ◽  
Operating Conditions ◽  
Active Area ◽  
Water Volume ◽  
Crossover Point

To achieve optimal performance of proton exchange membrane (PEM) fuel cells, effective water management is crucial. Cells need to be fabricated to operate over wide ranges of current density and cell temperature. To investigate these design and operational conditions, the present experiment utilized neutron radiography for measurement of in-situ water volumes of operating PEM fuel cells under varying operating conditions. Fuel cell performance was found to be generally inversely correlated to liquid water volume in the active area. High water concentrations restrict narrow flow field channels, limiting the reactant flow, and causing the development of performance-reducing liquid water blockages (slugs). The analysis was performed both quantitatively and qualitatively to compare the overall liquid water volume within the cell to the flow field geometry. The neutron image analysis results revealed interesting trends related to water volume as a function of time. At temperatures greater than 25°C, the total liquid water volume at start-up in the active area was the lowest at 1.5 A/cm2. At 25°C, 0.1 A/cm2 performed with the least amount of liquid water accumulation. However, as the reaction progressed at temperatures above 25°C, there was a crossover point where 0.1 A/cm2 accumulated less water than 1.5 A/cm2. The higher the temperature, the longer the time required to reach this crossover point. Results from the current density analysis showed a minimization of water slugs at 1.5 A/cm2, while the temperature analysis showed unexpectedly that, independent of current density, the condition with lowest water volume was always 35°C.

Measurement of Liquid Water Accumulation in a Proton Exchange Membrane Fuel Cell With Dead-Ended Anode

2008 ◽  
Author(s):  
Jason B. Siegel ◽  
Denise A. McKay ◽  
Anna G. Stefanopoulou
Keyword(s):  
Fuel Cell ◽  
Liquid Water ◽  
Voltage Drop ◽  
Cell Voltage ◽  
Gas Diffusion ◽  
Proton Exchange ◽  
Neutron Imaging ◽  
Water Dynamics ◽  
Water Flooding ◽  
Carbon Cloth

The operation and accumulation of liquid water within the cell structure of a polymer electrolyte membrane fuel cell (PEMFC) with a dead-ended anode is observed using neutron imaging. The measurements are performed on a single cell with 53 square centimeter active area, Nafion 111-IP membrane and carbon cloth Gas Diffusion Layer (GDL). Even though dry hydrogen is supplied to the anode via pressure regulation, accumulation of liquid water in the anode gas distribution channels was observed for all current densities up to 566 mA cm−2 and 100% cathode humidification. The accumulation of liquid water in the anode channels is followed by a significant voltage drop even if there is no buildup of water in the cathode channels. Anode purges and cathode surges are also used as a diagnostic tool for differentiating between anode and cathode water flooding. The rate of accumulation of anode liquid water, and its impact on the rate of cell voltage drop is shown for a range of temperature, current density, cathode relative humidity and air stoichiometric conditions. Neutron imaging of the water while operating the fuel cell under dead-ended anode conditions offers the opportunity to observe water dynamics and measured cell voltage during large and repreatable transients.

Operating Condition Optimization of PEMFC via Visualization Technique

2013 ◽  
Vol 393 ◽  
pp. 787-792 ◽  
Author(s):  
Khairul Imran Sainan ◽  
Wan Ahmad Najmi Wan Mohamed ◽  
Firdaus Mohamad ◽  
Norhisyam Jenal
Keyword(s):  
Fuel Cell ◽  
Liquid Water ◽  
Cell Voltage ◽  
Water Flooding ◽  
Root Cause ◽  
Condition Optimization ◽  
Dry Conditions ◽  
Voltage Performance ◽  
Stable Voltage ◽  
Membrane Dehydration

Fuel cell water management has two conflicting requirements; too less water causing membrane dehydration and too much water causing liquid water flooding. Both phenomena resulting in significantly instability voltage performance because of imbalance water presence. Therefore, it is vital to analyze and understand the root cause of the problem hence a 96cm2 transparent fuel cell was analyzed experimentally. The fuel cell allows clear visualization of flow channels, thus making it practical to analyze the transportation of reactants and products behavior. The experimental analyses were conducted under different reactant flow rate and inlet humidification variations. Highest cell performance was obtained under both reactant inlets humidification with largest air flow rates. On the other hand, when fuel and air in dry conditions, relatively lower cell voltage was obtained. Meanwhile, stable voltage was obtained under anode humidified and cathode non-humidified conditions with correct air to fuel ratio. Images of liquid water and voltage behavior are presented graphically corresponding to the changes in performance.

Direct Measurement of the Local Current Density Under Land-Channel Areas With Partially-Catalyzed MEAs

2012 ◽  
Author(s):  
Shan Jia ◽  
Hongtan Liu
Keyword(s):  
Fuel Cell ◽  
Current Density ◽  
Cell Voltage ◽  
Current Density Distribution ◽  
Cathode Side ◽  
High Cell ◽  
Land Area ◽  
Local Current Density ◽  
Local Current ◽  
Voltage Region

In a PEM fuel cell, local current density can vary drastically under the land and channel areas. The non-uniform current density distribution not only affects the overall performance of the fuel cell, but also leads to the local temperature and concentration differentiation on the MEA, which can cause problems such as membrane dehydration and catalyst degradations at certain locations. In order to investigate the local current performance, the objective of this work is to directly measure the local current density variations across the land and channel at the cathode in a PEM fuel cell with partially-catalyzed MEAs. First, the cathode flow plate is specially designed with a single-serpentine channel structure, and the gas diffusion electrode at cathode side is cut to fit this flow field size (5.0cm×1.3cm). Then five different partially-catalyzed MEAs with 1mm width corresponding to different locations from the middle of the gas channel to the middle of the land area are made. Fuel cells with each of the partially-catalyzed MEAs have been tested and the results provide the lateral current density distribution across the channel and the land areas. In the high cell voltage region, local current density is highest under the center of the land area and decreases toward the center of the channel area; while in the low cell voltage region local current density is highest under the middle of the channel area and decrease toward the center of the land area. Different flow rates are tested at the cathode side of the cell to study their effects on the local current density performance along the land-channel direction. And the results show that the flow rate barely has the effect on the current at the high cell voltage region, while it plays a significant role at the low voltage region due to the mass transport effect.

Two-Phase Transport in Proton Exchange Membrane Fuel Cells

1999 ◽  
Author(s):  
C. Y. Wang ◽  
Z. H. Wang ◽  
Y. Pan
Keyword(s):  
Fuel Cell ◽  
Current Density ◽  
Liquid Water ◽  
Proton Exchange Membrane ◽  
Threshold Current ◽  
Threshold Current Density ◽  
Proton Exchange ◽  
Air Cathode ◽  
Two Phase ◽  
Exchange Membrane

Abstract Proton exchange membrane (PEM) fuel cells have emerged, in the last decade, as a viable technology for power generation and energy conversion. Fuel cell (FC) engines for vehicular applications possess many attributes such as high fuel efficiency, low emission, quiet and low temperature operation, and modularity. An important phenomenon limiting fuel cell performance is the two-phase flow and transport of fuel and oxidant from flow channels to reaction sites. In this paper a mathematical model is presented to study the two-phase flow dynamics, multi-component transport and electrochemical kinetics in the air cathode, the most important component of the hydrogen PEM fuel cell. A major feature of the present model is that it unifies single- and two-phase analyses for low and high current densities, respectively, and it is capable of predicting the threshold current density corresponding to the onset of liquid water formation in the air cathode. A numerical study based on the finite volume method is then undertaken to calculate the detailed distributions of local current density, oxygen concentration, water vapor concentration and liquid water saturation as well as their effects on the cell polarization curve. The simulated polarization curve and predicted threshold current density corresponding to the onset of liquid water formation for a single-channel, 5cm2 fuel cell compare favorably with experimental results. Quantitative comparisons with experiments presently being conducted at our laboratory will be reported in a forthcoming paper.

Extracting Model Parameters and Paradigms From Neutron Imaging of Dead-Ended Anode Operation

2009 ◽  
Author(s):  
Jason B. Siegel ◽  
Anna G. Stefanopoulou ◽  
Serhat Yesilyurt
Keyword(s):  
Liquid Water ◽  
Front Propagation ◽  
Neutron Imaging ◽  
Model Parameters ◽  
Two Phase ◽  
Pde Model ◽  
Saturation Limit ◽  
Gravity Driven ◽  
Water Accumulation

In a PEMFC, feeding dry hydrogen into a dead-ended anode (DEA), reduces the overall system cost, weight and volume due to reduced need for a hydrogen-grade humidification and recirculation subsystems, but requires purging to remove the accumulated water and inert gas. Although the DEA method of operation might be undesirable due to its associated high spatial variability it provides a unique perspective on the evolution of the water accumulation in the anode. Sections of the channel nearest the inlets are significantly drier than those nearest the outlet as shown in the neutron imaging of a 53 cm2 PEMFC. This method allows in-situ visualization of distinct patterns, including water front propagation along the channels. In this paper we utilize neutron imaging of the liquid water distributions and a previously developed PDE model of liquid water flow in the GDL to (a) identify a range of numerical values for the immobile saturation limit, (b) propose a gravity-driven liquid flow in the channels, and (c) derive the two-phase GDL boundary conditions associated with the presence of liquid water in the channel.

The Effects of Feeding Configurations to Water Flooding and General Performance of a Proton Exchange Membrane Fuel Cell

2005 ◽  
Author(s):  
A. B. Mahmud Hasan ◽  
S. M. Guo ◽  
S. V. Ekkad
Keyword(s):  
Fuel Cell ◽  
Power Density ◽  
Current Density ◽  
Proton Exchange Membrane ◽  
Cell Voltage ◽  
Bipolar Plate ◽  
Proton Exchange ◽  
Water Flooding ◽  
Cathode Side ◽  
Exchange Membrane

The performance of a Proton Exchange Membrane Fuel Cell (PEMFC) using different feeding configurations has been studied. Three bipolar plates, namely serpentine, straight channel and interdigitated designs, were arranged in different combinations for the PEMFC anode and cathode sides. Nine combinations in total were tested under different flow rates, working temperatures and loadings. The cell voltage versus current density and the cell power density versus current density curves were obtained. After operating the PEMFC under high current densities, the cell was split and the water flooding in the feeding channels was visually inspected. Experimental results showed that for different feeding configurations, interdigitated bipolar plate in anode side and serpentine bipolar plate in cathode side had the best performance in terms of cell voltage-current density curve, power density output rate, percentage of flooded area in the feeding channels, the pattern of flooding and the fuel utilization rate.

The Nature of Flooding and Drying in Polymer Electrolyte Fuel Cells

2005 ◽  
Author(s):  
P. A. Chuang ◽  
A. Turhan ◽  
A. K. Heller ◽  
J. S. Brenizer ◽  
T. A. Trabold ◽  
...  
Keyword(s):  
Fuel Cells ◽  
Current Density ◽  
Liquid Water ◽  
High Current Density ◽  
Liquid Water Content ◽  
Small Mass ◽  
Neutron Imaging ◽  
Small Range ◽  
High Current ◽  
Voltage Loss

Two different 50 cm2 fuel cells operated at high current density (1.3A/cm2–1.5A/cm2) were visualized using neutron imaging, and the liquid water content in the flow channels and diffusion media under the lands and channels was calculated and compared. At high current density with fully humidified inlet flow, a direct comparison between flooded and non-flooded conditions was achieved by increasing the fuel cell temperature over a small range, until voltage loss from flooding was alleviated. Results indicate that a surprisingly small mass of liquid water is responsible for a significant voltage loss. The deleterious effects of flooding are therefore more easily explained with a locally segregated flooded pore model, rather than a homogeneously flooded pore and blockage phenomenon. Anode dryout was similarly observed and quantified, and results indicate that an exceedingly small mass of water is responsible for significant voltage loss, which is consistent with expectations. The results presented help to form a more complete vision of the flooding loss and anode dryout phenomena in PEFCs.

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