Management in PEM Fuel Cells
Humidification has to be carefully optimized in
PEM fuel cells.
Extremes in humidity levels at both the low end (membrane dehydration)
and the high end (cathode flooding) of the range can seriously reduce
PEMFC performance. Due to the conflicting requirements for a PEMFC
operation, the region of suitable operating conditions is very narrow.
The cell is usually operated at the flooding limit, and some areas of
the catalyst layer can easily become flooded by condensed water. Since
flooding has been identified as one of the main current-limiting
processes, understanding and optimizing liquid water transport
throughout the cell is critical to improving PEMFC performance.
Moreover, flooding can also take place at lower current densities, if
the gas flow rate and/or temperature (i.e. equilibrium vapor pressure)
Dusan Spernjak, PhD student
Professor Ajay K. Prasad
The gas diffusion layer (GDL) on the cathode side must remove product
water from the catalyst layer while still maintaining sufficient
membrane hydration. It is therefore vital to characterize the GDL
material’s ability to reach a steady state for mass transport
hydration level of the polymer membrane after step changes in cell
current draw. This is important in load-following applications, as well
as during startup and shutdown. Further, insight into liquid water
transport within the GDL pores and through the channels is needed to
optimize the design parameters and prevent electrode flooding.
One of our research goals has been to examine the properties of the
porous GDL media, and to evaluate their influence on the water and gas
transport. Furter, we are studying the effect of the microporous layer
(MPL) as well as the water dynamics in different flow field
configurations. We have designed an operational transparent PEM fuel
cell, which enables optical access to the flow field channels. We are
therefore able to visually characterize flooding in a working fuel
cell, while varying operating conditions, flow field design and GDL
material properties. The ultimate goal is to improve the cell
performance and durability through the efficient water management.
For more information, please visit Dusan Spernjak's
transparent PEM fuel cell.
visualization in an operational transparent PEM fuel cell.
Performance of the transparent cell with different GDL materials at same operating conditions.
Flow field visualization was performed simultaneously with the cell testing.