PEM Fuel Cell Membrane Hydration Measurement by Neutron Imaging

1
PEM Fuel Cell Membrane Hydration Measurement by
Neutron Imaging
D.J. Ludlowa, S.E. Morrisa, D.S. Husseyb, D.L.
Jacobsonb, M. Arifb, M.K. Jensena, and G.A.
Eismana aRPI, bNational Institute of Standards
and Technology
Pre-Processed Image

• APPROACH Neutron Imaging
• Hydrogen has a neutron scattering cross section
  significantly larger than other materials within
  a fuel cell
• Areas of high hydrogen concentration can be found
  by detecting the neutron flux attenuation
• Liquid water within the flow channels is easily
  detected

• Comparative image processing isolates water
  within the fuel cell
• When dividing a wet image with a dry image,
  the dry contribution drops out of the exponent
  resulting the isolation of water.

Post-Processed Image
Edge-View (Future)
Membrane Dehydration and Water Exchange

• Orient the fuel cell for image acquisition as an
  edge view.

• Special fixture to hold two pieces of membrane
  (alone) and expose to gas flow.
• Fully hydrate the membranes by boiling.
• Expose the membranes to dry gas while acquiring
  images.

• With high spatial resolution, water distributions
  across the width (y-axis) and thickness (x-axis)
  of the membrane can be resolved.
• High spatial resolution results in lower neutron
  counts per pixel, thus requiring increased
  integration times in order to support low
  uncertainties in water measurement.
• Thick (Nafion 117) membranes will be tested first
  to demonstrate distributed water measures across
  membrane and GDLs.

• Membrane fixture deformation during dehydration,
  and water droplets, resulted in large
  uncertainties and difficulty in image processing.

• Membranes hydrated with D2O were exposed to H2O
  humidified gas in an attempt to measure the
  exchange of D2O and H2O.
• Initial results indicate that additional
  measurements (impedance) might be helpful to
  isolate water exchange from hydration variation.

Conclusion Neutron imaging provides the ability
to measure membrane and gas diffusion layer
hydration in a distributed sense