The through-plane permeability of the gas diffusion media (GDM) is investigated experimentally with regard to the microporous layer (MPL) composition and the gas diffusion layer (GDL) composition and structure. The MPL composition is held constant at 80% carbon powder and 20% polytetrafluorethylene (PTFE) (by weight) for various carbon loadings. The decrease or increase in GDM permeability was found to be dependent on the structure of the GDL used in conjunction with the type of carbon powder. It was found that low-surface-area carbon powder (Vulcan XC-72R) forms thin, dense MPLs with small cracks when compared to high-surface-area powder (Ketjenblack EC-300J), which creates thick, rough MPLs with large cracks with increased carbon loadings. For most cases, the permeability decreases with increasing carbon loading; however, the non-woven, straight fibre carbon papers using Ketjenblack EC-300J show the lowest permeability at the lowest carbon loading. Furthermore, the percentage reduction from the GDL substrate permeability appears to be predictable for similar structures with increasing carbon loading. The increase in PTFE loading from 10% to 30% in the GDL was shown to have a significant impact on the percentage reduction from the original GDL permeability of $9% to 15% for the GDM composed of Vulcan XC-72R as carbon powder; however, such effects are insignificant when using Ketjenblack EC-300J carbon powder.

The through-plane gas permeability and morphology of PEFC gas diffusion media (GDM) is investigated for different microporous layer (MPL) ink homogenisation techniques (bath sonication and magnetic stirring) for low- (Vulcan XC-72R) and high (Ketjenblack EC-300J)-surface-area carbon powders. The MPL composition is held constant at 80 wt.% carbon powder and 20 wt.% PTFE for a carbon loading of 1.0 mg cm−2. The MPL ink homogenisation time is held constant at two hours for both techniques and increased by one hour for bath sonication to compare with previous investigations. The results show that the through-plane gas permeability of the GDM is approximately doubled using magnetic stirring when compared with bath sonication for MPLs composed of Vulcan XC-72R, with a negligible change in surface morphology between the structures produced from either homogenisation technique. The variation in through-plane gas permeability is almost negligible for MPLs composed of Ketjenblack EC-300J compared with Vulcan XC-72R; however, MPL surface morphology changes considerably with bath sonication, producing smoother, less cracked surfaces compared to the large cracks produced via magnetic stirring for a large-surface-area carbon powder. An MPL ink sonication time of three hours results in a percentage reduction in through-plane gas permeability from the GDL substrate permeability by ~72% for Ketjenblack EC-300J compared to ~47% for two hours.