Proceedings of EFC2011
European Fuel Cell - Piero Lunghi Conference & Exhibition
December 14-16, 2011, Rome, Italy
EFC11239
GAS DIFFUSION LAYER MATERIAL DEGRADATION MECHANISMS AND THEIR
EFFECT ON WATER BREAKTHROUGH DYNAMICS IN PROTON EXCHANGE
MEMBRANE FUEL CELLS
Matthew L. Garofalo and Satish G. Kandlikar
Mechanical Engineering Department
Rochester Institute of Technology
Rochester, New York, USA
ABSTRACT
The durability of the gas diffusion layer (GDL) and
microporous layer (MPL) in proton exchange membrane
fuel cells (PEMFCs) has not been heavily investigated and
further research is warranted. Accelerated stress tests
(ASTs) are required to degrade, analyze, and compare
components in a timely manner and, in turn, identify the
degradation mechanisms of GDLs. This work employs a
novel ex situ setup that degrades GDLs via an AST.
Capillary breakthrough pressure (CBP) measurement,
dynamic capillary pressure (DCP) observation, confocal
laser scanning microscopy (CLSM), and contact angle
(CA) measurement were employed for pre and post
mortem analyses. The fresh MPL surface maintained a
CA of 144° over a 45 minute period while the degraded
MPL surface CA decreased from 142° to 104° over the
same time frame. A change in DCP occurred and it is
suggested to be due to an increase of residual water
saturation within the GDL. This could, in turn, be linked to
a loss of hydrophobicity that occurred on the MPL surface.
INTRODUCTION
Despite their importance to PEMFC performance,
GDLs and MPLs have not been heavily investigated with
respect to degradation. The main degradation mechanism
of the GDL has been identified as the loss of
hydrophobicity and investigations on how this
phenomenon affects mass transport through the GDL are
called for (1). The water transport mechanisms through
GDLs directly characterize the accumulation of water
within them and are suspected to change over the cell
lifetime due to various degradation mechanisms of the
GDLs. The CBP and DCP are defined as the pressure at
which water breaks through the plane of an initially dry
GDL due to capillary force and recurrent pressure spike
phenomena respectively. A novel ex situ experimental
setup was designed in order to implement an AST for the
degradation of GDLs.
EXPERIMENT
The AST subjects the GDL to the following conditions
seen at the cathode side of a PEMFC for an extended
period of time:
 Constant accelerated current density
 Constant accelerated liquid water flow rate
 Typical fuel cell compression
 Typical fuel cell operating temperature
The experimental design shown in Figure 1 compresses
and seals the GDL and is able to purge the GDL sample
at any point in the AST to measure the CBP.
Figure 1: GDL degradation setup.
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The GDL tested was a 6.25 cm SGL Group Sigracet® 25
BC carbon fiber paper sample with a MPL. The AST
parameters used in this study are outlined in Table 1. The
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water flow rate is a theoretical cathode water production
rate and corresponds with the current density.
Table 1: Summary of AST conditions.
degraded GDL which includes a shorter drainage and
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imbibition process and therefore a 0.6 min shorter
pressure spike period. Also, the pressure reaches a value
of about 1.6 kPa lower and then drops to a value of about
2.75 kPa higher than before. This change suggests that
the residual saturation of water in the degraded GDL was
increased thus increasing the pressure to which the
imbibition curve falls to. This increase in residual water
saturation within the GDL could be linked to the loss of
hydrophobicity of the MPL.
The AST was applied to the GDL for 500 hours and the
CBP was measured before and after. The DCP and the
pressure spike frequencies were observed after the first
spike occurred. Before each CBP measurement, the GDL
was purged with purified air at 80 °C and 1 SLPM for two
hours to purge the GDL.
RESULTS
The MPL surface texture and hydrophobicity changed as
a result of the AST. A CLSM image of the degraded MPL
surface is shown in Figure 2.
Figure 2: CLSM image of degraded MPL surface.
The texture of the area under the channels where the
water passed (light region) changed more than the region
under the lands where the current was applied (dark
region). Figure 3 shows a MPL surface CA time study.
Figure 4: DCP of fresh (top) and degraded (bottom) GDL.
CONCLUSIONS
An ex situ experimental setup was employed to
degrade GDLs via an AST. A change in the GDL surface
texture occurred where the water was passed rather than
where the current was passed. A loss of hydrophobicity
occurred on the MPL surface which is proposed to be the
cause of the change in CBP as well as the DCP.
ACKNOWLEDGMENTS
Support for this project was provided by the US
Department of Energy under award No. DE-EE0000470.
Figure 3: Contact angle time study on MPL surface.
The fresh MPL surface maintained a CA of 144° over a 45
minute time period while the degraded MPL surface CA
decreased from 142° to 104° over the same time frame.
The plots in Figure 4 show a change in the DCP for the
REFERENCES
(1) Cho J, Ha T, Park J, Kim H, Min K, Lee E, Jyoung J.
Analysis of transient response of a unit protonexchange membrane fuel cell with a degraded gas
diffusion layer. International Journal of Hydrogen
Energy 2011;36(10):6090-6098.
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