Several techniques were used to characterize carbon cloth and carbon paper gas diffusion media (GDM). A technique for measuring the MacMullin number is described. This number provides the missing data to test the applicability of the commonly used Bruggeman equation. Analysis of the data show that only carbon cloth GDM follow the Bruggeman equation and that carbon paper GDM have a different relationship with porosity. Data obtained by using intrusion porosimetry (IP) and the method of standard porosimetry (MSP) for the hydrophilic and hydrophobic pore size distributions (PSD) is presented. The use of multiple working fluids to access hydrophilic and hydrophobic pores is discussed as well as limitations associated with structural changes of the GDM during the tests. Scanning electron microscopic (SEM) images are also presented to illustrate differences in structures. Finally, characteristics of the GDM are incorporated into a mass transport model in order to describe water phase distribution.
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