Differences in drying/wetting water transfer resistance through a platinum catalyst layer of a PEMFC electrode membrane

In order to understand the water transport phenomenon in a membrane electrode assembly (MEA), the water transfer resistance through a platinum catalyst layers (CL) is required. In this study, the overall water transfer resistance through the CL is taken as the sum of the resistance to charge/discharge water from the surface of ionomer in the CL and the resistance for water to pass through the ionomer in the CL. The value of this quantity for a CL that is 4 [im thick and is coated on a 178 [im thick Nation 117, was estimated. The MEA was dried/wetted by supplying gas with controlled humidity to the surface of the MEA. The water concentration contained in the PEM was measured by nuclear magnetic resonance (NMR) using a small detection coil. The rates of drying/wetting of the MEA were calculated from time-dependent changes of the water concentration measured in the PEM. The overall water transfer resistance through a CL was estimated by comparing experiment and analytical results based on the analytical model. As a result, the overall water transfer resistances through the 4 [im thick CL during drying and wetting were 0-3 x 104 and 10 ± 6 x 104 s/m, respectively.