College Park, Maryland      June 6 - 10 , 2004

T1-A4 (9:30 AM): On-line studies of electric fuel cell assemblies by neutron imaging methods

D. Kramer, G. Scherer (Paul Scherrer Institut, General Energy Department, Electrochemistry Laboratory, CH-5232 Villigen PSI, Switzerland), E. Lehmann (Paul Scherrer Institut, Research Department Condensed Matter Research with Neutrons and Muons, CH-5232 Villigen PSI, Switzerland), J. Zhang (NISSAN Motor Co. Ltd., Powertrain and Environmental Research Laboratory, 1 Natsushima-cho, Yokosuka 237-8523, Japan), K.N. Clausen (Paul Scherrer Institut, Research Department Condensed Matter Research with Neutrons and Muons, CH-5232 Villigen PSI, Switzerland)

Fuel cells are envisaged a key role for the development of the so-called hydrogen economy or for the future of individual transport systems in cities and other mobile applications . In Electric fuel cells hydrogen, natural gas or methanol in combination with oxygen is converted into electric power and non-poisonous reaction products (Water and CO2). The development of efficient, long lived, light, low cost fuel cells is therefore high on the agenda and many research groups world wide are studying both materials for use in fuel cells and their behavior during operation of the cell.

One of the reaction product for low temperature operation conditions within fuel cells is water, and since the humidity inside the so-called gas diffusion layer of the fuel cell, strongly influences the behavior and the performance of the whole assembly, it is of great interest to follow the production of water and how this water is transported out of the cell simultaneously with measurements of the local current density in an operating fuel cell.

Because of the high neutron attenuation coefficient for hydrogen in comparison to the structural materials of the fuel cell (carbon, aluminum etc.), the quantitative distribution of water can be studied by neutron imaging techniques.

The radiography beam line NEUTRA at the spallation neutron source SINQ has been used for such in situ studies of operating test fuel cells. The accumulation and distribution of water was studied both with a coarse time resolution with integration over about 10 s or very fast with up to 30 frames per second. In the first case, the image quality allowed for quantitative determination of the water distribution. In the later case, short term changes in the flow field could be detected.

The paper will describe in detail the experimental setup, the methodology to derive quantitative values for the water distribution from the neutron images and first results from a test cell. An outlook for further developments of the method will be given.

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