While direct and indirect photolysis systems produce pure hydrogen, dark — fermentation and photo-fermentation processes, produce a mixed-biogas — containing primarily hydrogen and carbon dioxide (CO2), but which may also contain lesser amounts of methane (CH4), carbon monoxide (CO) and/or hydrogen sulphide (HjS) or ammonia (NH3). Moreover, the hydrogen content in the gas phase is in general lower than 50%. PEMFCs require hydrogen at a high purity (>99%) and cannot tolerate CO at concentrations higher than 10 ppm. In order to remove diluting (CO2, CH4) and/or contaminating (CO) gases, purification of the biogas is essential. Up to now, membrane technologies based on palladium have been proposed as hydrogen purifier in industrial scale applications (Shu et al, 1991).