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Movement of Water in Fuel Cell Electrodes (Allen)

A method for measuring the contact angle of liquids on rough surfaces quickly and accurately has been developed. Understanding the wettability of Gas Diffusion Layers (GDLs) will aid in developing fuel cells materials resistant to flooding. An environmental enclosure has been fabricated to control temperature and humidity when taking images of water drops on GDLs. The enclosure includes a thermal stage which can heat or cool a GDL sample.  

An idea of spatial differences may be noted by using similar sized drops on different areas of the same GDL.   Table 1 lists contact angle measurements for multiple drops on three different GDL samples.  Generally, the data is consistent; especially for a rough surface with very small drops.  The Bond numbers for the drops were between 10-3 and 10-2.  The deposition of the drop is critical and is likely responsible for some of the variation shown in.  This work was conducted by Russell Stacy (MS) with assistance from David Fritz (PhD).

The SEM imaging mount has been redesigned to allow for measurement of force and sample compression.  The main objective is to image a compressed sample inside the SEM. The initial design had an outer ring which compressed the samples. The boundaries between the compressed and uncompressed areas could then be viewed by focusing on the plane of the GDL.  Compression by a fuel cell flow field was simulated by adding a channel along the middle of the base plate and on the bottom of the top plate.  This configuration allowed for the top plate to be rotated with respect to the bottom plate creating multiple different scenarios. Imaging could be done with a micro-channel under the GDL and a flat surface above, as well as the micro-channel on top of the GDL and a flat surface below or a micro-channel on the top and the bottom of the GDL. These ideas were reused in the new design, the base plate again has a channel through it, and the middle plate has a channel on the bottom side.  The newly designed SEM mount has a slot machined into each of the top plates that allow for a test dial indicator to probe the displacement of each plate. Figure 1 illustrates the sample holder.  This work was completed by Joseph Lechnyr (MS) and David Fritz (PhD).

Table 1 . Contact angle data for three GDL samples.  The SGL Carbon 25 BC sample had the highest average contact angle and the largest deviation.  The Freudenberg nonwoven samples showed a 4 degree increase in the contact angle after application of the MPL layer.

 

drop height, cm

equatorial
radius, cm

 

b

contact angle

MTU GDL #7

.24

.318

.16

153.55

 

.24

.318

.17

144.20

 

.23

.319

.15

154.99

 

.19

.318

.13

140.69

MTU GDL #8

.20

.319

.14

134.09

 

.20

.318

.14

134.26

 

.20

.318

.14

134.77

 

.25

.222

.19

142.28

MTU GDL #9

.21

.318

.15

138.00

 

.23

.318

.17

137.26

 

.22

.318

.16

135.80

 

.24

.318

.17

140.15

 

.24

.236

.17

141.61

4 

Plans for Next Quarter and Key Issues: Include purchasing the final equipment and supplies for next quarter. Anticipate delivery of all necessary equipment and instrumentation. This will greatly facilitate completion of all our project objectives.

Publications:  Allen, J. S., Son, S. Y., and Collicott, S. H., "PEMFC Flow-Field Design for Improved Water Management", Handbook of Fuel Cells – Fundamentals, Technology and Applications, W. Vielstich, H.A. Gasteiger and H. Yokokawa (Eds.), Volume 5: Advances in Electrocatalysis, Materials, Diagnostics and Durability, John Wiley & Sons Ltd., accepted for publication (2008).

 

 


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