Rod L Borup

Imaging of Water Profiles in PEM Fuel Cells Using Neutron Radiography: Effect of Operating Conditions and GDL Composition

The performance of polymer electrolyte membrane (PEM) fuel cells as a function of cathode inlet relative humidity (RH) and gas diffusion layer (GDL) properties has been characterized. The performance of 50 cm2 fuel cells at high current densities was a strong function of the polytetrafluoroethylene (PTFE) content in the cathode GDL microporous layer (MPL). The voltage at a current density of 1.4 A cm-2 decreased at all inlet RHs as the PTFE content in the cathode MPL increased from 5 % by weight to 23 % by weight. This was associated with a corresponding increase in the mass transport resistance as measured by AC impedance. The low frequency resistance also increased with increasing cathode inlet RH. These results were validated by high-resolution neutron radiography on specially designed 2.25 cm2 cells that showed increased water content in the GDLs at high inlet RHs and high microporous layer PTFE content. High-resolution neutron imaging also revealed higher water concentrations at the outlets, cathode GDL, anode flow channel, and MEA/GDL above the land when compared to the inlets, anode GDL, cathode flow channel, and MEA/GDL above the channel respectively.