|Title||Accurate measurement of the through-plane water content of proton-exchange membranes using neutron radiography|
|Publication Type||Journal Article|
|Year of Publication||2012|
|Authors||Hussey, Daniel S., Dusan Spernjak, Adam Z. Weber, Rangachary Mukundan, Joseph Fairweather, Eric L. Brosha, John Davey, Jacob S. Spendelow, David L. Jacobson, and Rodney L. Borup|
|Journal||Journal of Applied Physics|
|Keywords||electrolyte fuel-cells, in-situ, liquid water, microchannel plate detectors, model, nafion, polymer electrolytes, schroeders-paradox, transportation, x-ray-scattering|
The water sorption of proton-exchange membranes (PEMs) was measured in situ using high-resolution neutron imaging in small-scale fuel cell test sections. A detailed characterization of the measurement uncertainties and corrections associated with the technique is presented. An image-processing procedure resolved a previously reported discrepancy between the measured and predicted membrane water content. With high-resolution neutron-imaging detectors, the water distributions across N1140 and N117 Nafion membranes are resolved in vapor-sorption experiments and during fuel cell and hydrogen-pump operation. The measured in situ water content of a restricted membrane at 80 degrees C is shown to agree with ex situ gravimetric measurements of free-swelling membranes over a water activity range of 0.5 to 1.0 including at liquid equilibration. Schroeder's paradox was verified by in situ water-content measurements which go from a high value at supersaturated or liquid conditions to a lower one with fully saturated vapor. At open circuit and during fuel cell operation, the measured water content indicates that the membrane is operating between the vapor-and liquid-equilibrated states.
|Short Title||J. Appl. Phys.|