This work presents an experimental method that is one of the few to allow both imbibition and drainage capillary measurement at pressures above breakthrough. It was used on Toray and SGL Carbon gas diffusion materials at room temperature. These materials exhibited both hydrophobic and hydrophilic properties. Breakthrough pressures for Toray and SGL Carbon were 3.6 and 1.5 kPa, respectively. Little hysteresis was observed in these room-temperature experiments, which is an interesting contrast with the results from the only other group, Schwartz's group at University of Washington, to measure these properties. A double exponential equation was used to fit the data for each carbon paper.

In a hydrogen PEM fuel cell (PEMFC), liquid water is generated as a by-product (O2 + 4 H+ + 4 e- ↔ 2H2O) at the cathode during operation. The presence of liquid water results in a two-phase (gas/liquid) condition in the porous media, such as, the gas diffusion and catalyst layers. In a direct methanol PEM fuel cell (DMFC), in addition to the two-phase condition in the cathode similar to that of a hydrogen PEMFC, another two-phase condition also exists in the anode when gaseous carbon dioxide is generated as a by-product (CH3OH + H2O ↔ CO2 + 6 H+ + 6 e-) during operation. These two-phase conditions affect the transport rates of the reactants (oxygen and methanol/water) to the reactive sites in the electrodes. Knowledge of two-phase transport properties of the porous media used in PEMFCs and DMFCs is required to develop materials that will result in optimal fuel cell performance. This paper discusses the techniques that we have developed for measuring two-phase transport properties of porous media used in PEMFCs and DMFCs and the results obtained for some commercially available materials.

Capillary pressure curve is used to account for the mass transport limitation in the porous gas diffusion layer (GDL) in modeling two-phase phenomena in conventional distributors. Various assumptions and approximations on capillary pressure curve have been made to develop models. To date the capillary pressure curve in gas diffusion medium in PEM fuel cell does not seem to have been obtained. In this study, volume displacement technique and neutron imaging technique that can obtain capillary pressure curve in gas diffusion material is described. An experimental data of capillary pressure curve of porous material used in PEM fuel cell will help two-phase models of PEM fuel cell to be more accurate in their predictions of fuel cell behaviors.

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