Confined water distribution in the ionomer within the catalyst layers of polymer electrolyte fuel cells; A Small-angle neutron scattering study

Iwase, Hiroki*; Arima, Hiroshi*; Harada, Masashi*; Kumada, Takayuki   

The humidity dependence of the structure of catalyst-coated membranes in polymer electrolyte fuel cells (PEFCs) was investigated using small-angle neutron scattering (SANS). The results showed that the water volume in the ionomer linearly increases with humidity from an intermediate humidity (50% RH), reaching values similar to those observed in the polymer electrolyte membrane (PEM) at 80% RH. Time-resolved SANS reveals that the catalyst layer binds water more strongly than the PEM. Water distribution in the ionomers within the catalyst layers of an operating PEFC (80 degree, 80% RH) increased with the increase in the current density, affecting its PEFC performance. The behavior of the water distribution in the catalyst layers was closer to that of the water distribution in the gas diffusion layers than that in the PEM.