It is known that the mass transfer characteristics of the gas diffusion layer (GDL) are closely related to the performance of a proton-exchange membrane fuel cell. In this study, an experimental method was established for measuring the gas diffusion coefficient in porous media by using an oxygen concentration sensor based on a galvanic battery operating at normal temperature. The oxygen diffusion coefficient in air measured by this method corresponded with data in the literature within ±6% deviation. The oxygen diffusion coefficients of two kinds of porous media generally used for the GDL were measured by the experimental method for dry and wet samples. The results indicate that the gas diffusion coefficient in porous media not only depends on porosity but is also affected by other factors, for example, tortuosity. It was also found that the diffusion coefficient in different directions, for example, through-plane and in-plane, in porous media can be very different. The oxygen diffusion coefficient in the porous media containing liquid water varied nonlinearly with the saturation level and was strongly affected by other factors as well.

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