Water Distribution Analysis in the Outer Perimeter Region of Technical PEFC Based on Neutron Radiography

Abstract

This work focuses on water transport behavior in PEFC, particularly in the area situated between flowfield and sealing gasket. An in situ investigation of fundamental water and gas transport effects in this edge region was performed by means of neutron radiography. Five different 50 cm2 test cell setups were operated, basically differing in the applied sealing solution, whereby it was accounted for the requirements posed by metallic bipolar plates. Main influencing factors on the water transport were identified, namely channel geometry, gas inlet humidification, temperature and gas pressure under static and dynamic conditions. It was found that the design of the edge region can have a significant influence on water transport properties and water accumulation in the cell. Depending on its gas accessibility, the edge region can act as a reservoir for water accumulation. Time constants for water transport can be shifted to the range of hours, which is crucial for an effective water removal as it is essential for cold starts. In addition, relatively wide edge channels, as required for sub-gasket based cell setups, can enable strong bypass flows around the flowfield and thus lower the effective stoichiometry, which can have a significant impact on the water content in the flowfield.