Characterization of Fuel Cells and Fuel Cell Systems Using Three-Dimensional X-Ray Tomography

2006 ◽  
Vol 4 (1) ◽  
pp. 84-87 ◽  
Author(s):  
Stefan Griesser ◽  
G. Buchinger ◽  
T. Raab ◽  
D. P. Claassen ◽  
Dieter Meissner
Keyword(s):  
Fuel Cells ◽  
Fuel Cell ◽  
Ionic Conductivity ◽  
First Generation ◽  
Mechanical Stability ◽  
Three Dimensional ◽  
Gas Diffusion ◽  
Critical Parameters ◽  
Electrode Layer ◽  
X Ray

Three dimensional (3D) computer aided X-ray tomography (CT) has proven to be an extremely useful tool in developing our own as well as in examining commercially available solid oxide fuel cells. The results of 3D-CT measurements became very important for understanding the functionality of our first generation and improving the development of our second fuel cell generation. Also geometrical measurements, especially the roundness and the straightness of the tube, can be evaluated, both critical parameters when the stack is heated and mechanical stress has to be avoided. By using this technique the structure of the first generation cells proved to be of insufficient quality. Problems like the variation in thickness of the electrolyte tube as well as the homogeneity in thickness of the electrodes deposited can easily be detected by this nondestructive technique. Microscopic investigations of this problem of course provide equal results, but only after cutting the samples in many slices and many single measurements of different areas of the fuel cell. Using cells with inhomogeneous thickness of course results in drastic variations of the current densities along a single cell. Electrolyte layers that are too thick will result in power loss due to the increased resistance in the ionic conductivity of the electrolyte. If the electrolyte of an electrolyte supported cell is too thin, this can cause mechanical instability. Problems can also occur with the leak tightness of the fuel cell tube. Gas diffusion through the electrode layer can become a problem when the thickness of the electrode layer is too high. On the other hand, if the layers are too thin, the result can be a discontinuous layer, leading to a high electrical series resistance of the electrode. Besides determining the thickness variations also the porosity of the electrolyte needs careful attention. Larger cavities or shrink holes form insulating islands for the ion-stream and are therefore limiting the ionic conductivity. They are also diminishing the mechanical stability and provide problems for depositing a closed electrode film in electrode supported cells.

Effect of Vibration on the Liquid Water Transport of PEM Fuel Cells

2009 ◽  
Author(s):  
Luis Breziner ◽  
Peter Strahs ◽  
Parsaoran Hutapea
Keyword(s):  
Fuel Cells ◽  
Fuel Cell ◽  
Water Transport ◽  
Liquid Water ◽  
Pem Fuel Cells ◽  
Gas Diffusion ◽  
Cell Performance ◽  
Sinusoidal Vibration ◽  
Fuel Cell Performance ◽  
Liquid Water Transport

The objective of this research is to analyze the effects of vibration on the performance of hydrogen PEM fuel cells. It has been reported that if the liquid water transport across the gas diffusion layer (GDL) changes, so does the overall cell performance. Since many fuel cells operate under a vibrating environment –as in the case of automotive applications, this may influence the liquid water concentration across the GDL at different current densities, affecting the overall fuel cell performance. The problem was developed in two main steps. First, the basis for an analytical model was established using current models for water transport in porous media. Then, a series of experiments were carried, monitoring the performance of the fuel cell for different parameters of oscillation. For sinusoidal vibration at 10, 20 and 50Hz (2 g of magnitude), a decrease in the fuel cell performance by 2.2%, 1.1% and 1.3% was recorded when compared to operation at no vibration respectively. For 5 g of magnitude, the fuel cell reported a drop of 5.8% at 50 Hz, whereas at 20 Hz the performance increased by 1.3%. Although more extensive experimentation is needed to identify a relationship between magnitude and frequency of vibration affecting the performance of the fuel cell as well as a throughout examination of the liquid water formation in the cathode, this study shows that sinusoidal vibration, overall, affects the performance of PEM fuel cells.

Prediction the Differences of Permeability Between Carbon Fiber Paper and Carbon Fiber Cloth in PEM Fuel Cells

2011 ◽  
Author(s):  
Yuan Gao
Keyword(s):  
Fuel Cells ◽  
Carbon Fiber ◽  
Pem Fuel Cells ◽  
Gas Diffusion ◽  
Anisotropic Permeability ◽  
Gas Diffusion Layers ◽  
X Ray ◽  
Diffusion Layers ◽  
Carbon Fiber Cloth ◽  
Carbon Fiber Paper

This study is using the multiple relaxation time Lattice Boltzmann method to calculate the permeability of carbon fiber paper and carbon fiber cloth gas diffusion layers (GDL). The 3D gas diffusion layers are generated by X-ray computed tomography, This method involve generation of 3D digital model of gas diffusion layers acquired through X-ray micro-tomography at resolution of a few micros. The reconstructed 3D images were then read into the LBM model to calculate the anisotropic permeability of carbon fiber paper and carbon fiber cloth GDL. We investigated the relationships between the anisotropic permeability and porosity and compare the difference between the two different kinds of GDLs when they have the similar porosity. We also calculate the permeability with different viscosity and compare the two results from the carbon fiber paper and carbon fiber cloth. It is useful for selection of materials for high performance gas diffusion media and can improve the performance of the fuel cells.

scholarly journals Quantifying phosphoric acid in high-temperature polymer electrolyte fuel cell components by X-ray tomographic microscopy

2014 ◽  
Vol 21 (6) ◽  
pp. 1319-1326 ◽  
Author(s):  
S. H. Eberhardt ◽  
F. Marone ◽  
M. Stampanoni ◽  
F. N. Büchi ◽  
T. J. Schmidt
Keyword(s):  
High Temperature ◽  
Fuel Cell ◽  
Phosphoric Acid ◽  
Polymer Electrolyte ◽  
Diffusion Layer ◽  
Gas Diffusion Layer ◽  
Gas Diffusion ◽  
X Ray ◽  
Wide Range ◽  
Cell Components

Synchrotron-based X-ray tomographic microscopy is investigated for imaging the local distribution and concentration of phosphoric acid in high-temperature polymer electrolyte fuel cells. Phosphoric acid fills the pores of the macro- and microporous fuel cell components. Its concentration in the fuel cell varies over a wide range (40–100 wt% H3PO4). This renders the quantification and concentration determination challenging. The problem is solved by using propagation-based phase contrast imaging and a referencing method. Fuel cell components with known acid concentrations were used to correlate greyscale values and acid concentrations. Thus calibration curves were established for the gas diffusion layer, catalyst layer and membrane in a non-operating fuel cell. The non-destructive imaging methodology was verified by comparing image-based values for acid content and concentration in the gas diffusion layer with those from chemical analysis.

Investigation of Thermal Influence on the Assembly of Polymer Electrolyte Membrane Fuel Cell Stacks

2012 ◽  
Vol 512-515 ◽  
pp. 1509-1514
Author(s):  
Lin Fa Peng ◽  
Dian Kai Qiu ◽  
Pei Yun Yi ◽  
Xin Min Lai
Keyword(s):  
Thermal Expansion ◽  
Fuel Cell ◽  
Contact Pressure ◽  
Proton Exchange Membrane ◽  
Three Dimensional ◽  
Gas Diffusion ◽  
Proton Exchange ◽  
Membrane Electrode ◽  
Fe Model ◽  
Assembly Process

The assembly force in a proton exchange membrane fuel cell (PEMFC) stack affects the characteristics of the porosity and electrical conductivity. Generally, the stack is assembled at room temperature while it’s operated at about 80 °Cor even higher. As a result, the assembly pressure can’t keep constant due to thermal expansion. This paper focuses on the contact pressure between membrane electrode assembly (MEA) and bipolar plates in real operations. A three-dimensional finite element (FE) model for the assembly process is established with coupled thermal-mechanical effects. The discipline of contact pressure under thermal-mechanical effect is investigated. A single cell stack is fabricated in house for the analysis of contact pressures on gas diffusion layer at different temperatures. The results show that as the temperature increases, contact pressure increases due to thermal expansion. It indicates that the influence of thermal expansion due to temperature variation should be taken into consideration for the design of the stack assembly process.

Fluorescence Microscopy for the Measurement of the Surface Properties of the Gas Diffusion Layers of Fuel

2010 ◽  
Author(s):  
Brooks Friess ◽  
Mina Hoorfar
Keyword(s):  
Water Management ◽  
Fuel Cells ◽  
Fuel Cell ◽  
Fluorescence Microscopy ◽  
Pem Fuel Cells ◽  
Gas Diffusion ◽  
Experimental Methodology ◽  
Test Fluid ◽  
Average Height ◽  
Wetted Area

One of the major problems of current proton exchange membrane (PEM) fuel cells is water management. The gas diffusion layer (GDL) of the fuel cell plays an important role in water management since humidification and water removal are both achieved through the GDL. Various numerical models developed to illustrate the multiphase flow and transport in the fuel cell require the accurate measurement of the GDL properties (wettability and surface energy). In a recent study, the capillary penetration technique has been used to measure indirectly the wettability of the GDL based on the experimental height penetration of the sample liquid into the porous sample. In essence, a high resolution microscope/camera was used to detect the rate of penetrated height into the sample GDL. The shortcoming of this type of visualization is that it can only be used for thin hydrophilic GDL samples with zero Teflon loadings. For the thick and high Teflon loading GDLs, there is not enough contrast to detect the height of the penetrated liquid. In the real fuel cells, the GDLs are made of the micro-porous and macro-porous layers with an optimum Teflon loading. Therefore, it is required to develop a new experimental methodology capable of detecting the rate of penetration and as a result the wettability of GDLs samples used in fuel cells. In this paper, the fluorescence microscopy technique is integrated into the experimental setup of the capillary penetration method to improve the contrast between the wetted and non-wetted area. The fluorescence setup uses a powder die, dissolved in the test fluid, which is excited by a concentrated ultraviolet light illuminated in the vertical manner. To acquire the profile images of the penetrated liquid, an optical mirror was used. This new setup has the added advantage of providing a visual representation of the different regimes of penetration (e.g., the fingering effect reported for the pathways of the liquid penetrated into the GDLs) that are defined by the capillary number and mobility ratio of each fluid. Since the GDL samples used in this study are relatively hydrophobic (e.g., with 40% Teflon loadings), the pattern of liquid penetration is not uniform. Thus, an image analysis program was developed to determine the average height of penetration based on the area under the entire wetted area. The general Washburn equation was then used to fit the extracted height data and provide the average internal contact angle for each test liquid.

Computational Modelling and Simulation of Proton-Exchange Membrane Fuel Cells (Keynote)

2002 ◽  
Author(s):  
N. Djilali ◽  
T. Berning
Keyword(s):  
Fuel Cells ◽  
Fuel Cell ◽  
Proton Exchange Membrane ◽  
Transport Phenomena ◽  
Computational Modelling ◽  
Ambient Air ◽  
Gas Diffusion ◽  
Transport Processes ◽  
Proton Exchange ◽  
Exchange Membrane

Fuel cells (FC’s) are electrochemical devices that convert directly into electricity the chemical energy of reaction of a fuel (usually hydrogen) with an oxidant (usually oxygen from ambient air). The only by-products in a hydrogen fuel cell are heat and water, making this emerging technology the leading candidate for quiet, zero emission energy production. Several types of fuel cell are currently undergoing intense research and development for applications ranging from portable electronics and appliances to residential power generation and transportation. The focus of this lecture is Proton-Exchange Membrane Fuel Cells (PEMFC’s). An electrolyte consisting of a “solid” polymer membrane, low operating temperatures (typically below 90 °C) and a relatively simple design combine to make PEMFC’s particularly well suited to automotive and portable applications. The operation of a fuel cell relies on electrochemical reactions and an array of coupled transport phenomena, including multi-component gas flow, two phase-flow, heat and mass transfer, phase change and transport of charged species. The transport processes take place in variety of media, including porous gas diffusion electrodes and polymer membranes. The fuel cell environment makes it impossible to measure in-situ the quantities of interest to understand and quantify these phenomena, and computational modelling and simulations are therefore poised to play a central role in the development and optimization of fuel cell technology. We provide an overview of the role of various transport phenomena in fuel cell operation and some of the physical and computational modelling challenges they present. The processes will be illustrated through examples of multi-dimensional numerical simulations of Proton-Exchange Membrane Fuel Cells. We close with a perspective on some of the many remaining challenges and future development opportunities.

Phase-contrast X-ray imaging of the gas diffusion layer of fuel cells

2010 ◽  
Vol 17 (6) ◽  
pp. 813-816 ◽  
Author(s):  
S. Takeya ◽  
A. Yoneyama ◽  
J. Miyamoto ◽  
Y. Gotoh ◽  
K. Ueda ◽  
...  
Keyword(s):  
Fuel Cells ◽  
Diffusion Layer ◽  
Phase Contrast ◽  
Gas Diffusion Layer ◽  
Gas Diffusion ◽  
X Ray ◽  
X Ray Imaging
Sign in / Sign up

Export Citation Format

Share Document