Transport Phenomena
Visualization Techniques (Neutron Radiography)
Quantifying mass transport in electrochemical energy systems requires advanced techniques to capture microscopic detail. Neutron imaging is similar but complimentary to x-ray imaging, and far superior at penetrating through materials associated with fuel cell or battery designs, allowing for non-destructive observation of internal phenomena. The advantage of neutrons compared to x-rays is their ability to image light elements (hydrogen, water, carbon, etc.) while penetrating heavy elements (lead, titanium, etc.). For example water accumulation in hydrogen fuel cells can be captured visually since neutrons will pass through metallic or carbon bi-polar plates but not through water. This is analogous to x-rays which pass through water but not through materials such as bone which show up in images. Because neutrons interact with the nucleus rather than with the electron shell, they can also distinguish between different isotopes of the same element. This makes neutron radiography an important tool in various research applications and in the field of electrochemical energy systems.
Below is an example of the difference in detail of an SLR camera captured by x-ray vs. neutron images (x-ray on left, neutron on right):
3D Neutron Tomography of Fuel Cells
Neutron images are 2D data sets called radiographs, these may be assembled into 3D models via a method called tomography. Tomography allows for full reconstruction of a sample which gives researchers rich detailed information as to liquid water distribution or material structure. For fuel cells this is a valuable tool for analysis of water or ices formation that may effect system performance.
Below is an image of a fuel cell designed for tomography. The cell is made of nickel coated aluminum to allow for clear neutron penetration, it is circular to fit inside an environmental chamber that can be used to control temperature. To the right is an example of tomography data. The cell has been scanned over 180 degrees to capture image data (similar to an MRI) and then this data is "sliced" at points of interest. This image highlights liquid water that was imaged inside the fuel cell, such information is valuable to cell designers.
