|Neutron image of water formed inside fuel cell during operation. Source: NIST|
A new and improved imaging instrument at the Commerce Department&s National Institute of Standards and Technology (NIST) allows researchers to visualize water production and removal in fuel cells under a range of simulated operating conditions, from arctic cold to desert heat.
The newly commissioned Neutron Imaging Facility offers visualization powers 10 times better than those achieved previously. It can produce still images akin to CAT scans and record movie at a rate of up to 30 frames per second, or 30 times faster than a first-generation instrument.
The new system can reveal water quantities smaller than 1 microgram (millionth of a gram, and show details as small as 0.02 millimeter in images. Even better spatial resolution is expected.
This as-it-happens, inside view is essential because fuel-cell performance depends on a delicate balance. Too little—or too much—water can shut it down.—Muhammad Arif, NIST team leader
The new facility is located at the NIST Center for Neutron Research (NCNR), where NIST researchers first adapted the imaging technique so that it could be used to peer inside fuel cells. Initial proof-of-concept experiments were carried out in 1997.
The new research station is operated as a national user facility, open to scientists from industry, universities, and government agencies. It is jointly funded by NIST, the Department of Energy and General Motors. Results of non-destructive neutron-imaging studies will guide work to optimize flows and concentrations of water in the serpentine channels of fuel cells.
The system uses cone-shaped beams of neutrons to penetrate the fuel-cell structure. Unlike X-rays, neutrons can pass nearly unimpeded through the solid encasements, but they interact strongly with hydrogen. As a result, neutron beams are highly sensitive probes of water, since each molecule contains two hydrogen atoms.
The imaging facility also incorporates safety features and a comprehensive infrastructure to support advanced fuel-cell testing. NIST researchers plan to make additional enhancements, especially in neutron detector technology. This would further improve resolution and reduce the time required to capture an image.
In addition, initial efforts aimed at high-speed, three-dimensional imaging capabilities show promise. The approach, now under development, borrows from astronomical and medical imaging methods.
NIST PEM Fuel Cell movie