On the gas permeability of the microporous layer used in polymer electrolyte fuel cells

In an attempt to obtain accurate values of the gas permeability of the microporous layer (MPL), substrates with negligible MPL penetration and of known gas permeability, i.e. membrane filters, have been employed. The values of the MPL permeability obtained using the membrane filters were compared with those obtained conventionally using the carbon substrates. Due to MPL penetration, the MPL permeability obtained using the carbon substrate were found to decrease with carbon loading. On the other, due to negligible penetration, the MPL permeability obtained using the membrane filters were found to be almost invariant with the carbon loadings. Furthermore, the MPL permeability was found to be sensitive to the substrate used: more cracks (and subsequently substantially higher permeability) were shown by the MPLs coating the carbon substrates. This implies that the MPLs coating the carbon substrates and the MPLs coating the membrane filters are structure-wise different. It subsequently means that the MPL permeability obtained using the membrane filters cannot be used to estimate the MPL penetration into the carbon substrates.