Measurements of Two-Phase Flow Properties of the Porous Media Used in PEM Fuel Cells

Abstract

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.