Porous fuel cell separator including a vapor permeable layer

A porous fuel cell separator (30) comprises a water vapor permeable layer (36) on at least one portion of the porous plate such as on the ribs (32), on the channel walls or within the porous separator (not shown). The vapor permeable layer (36) preferably compising poly-dimethyl-siloxane (PDMS) is configured to permit water vapor (52) to pass whilst preventing liquid such as coolant from passing therethrough.The water vapor serves (52) for humidifying the reactant gas stream (50) prior to arriving at the MEA (22).