Measurement of MacMullin Numbers for PEMFC Gas-Diffusion Media

A technique for measuring the MacMullin number is described and the values are reported for different carbon-cloth and carbon-paper gas-diffusion media (GDM). This number provides the missing data to test the applicability of the commonly used Bruggeman equation for these porous structures. Analysis of the MacMullin number and porosity data show that only carbon-cloth GDM follow the Bruggeman equation and that carbon-paper GDM has a different relationship with porosity. These differences are discussed in terms of path length created by the orientation of fibers of each GDM.