An innovative small-scale cogeneration system based on membrane reformer and PEM fuel cells is under development within the FIuidCELL project. An experimental campaign has been carried out to characterize the PEM fuel cell and to define the operative conditions when integrated within the system. The hydrogen feeding the PEM is produced by a membrane reactor which in principle can separate pure hydrogen; however, in general, hydrogen purity is around 99.9%-99.99%. The focus of this work is the assessment of the PEM performance under different hydrogen purities featuring actual membrane selectivity and gases build-up by anode off-gas recirculation. Their effects on the cells voltage and local current distribution are measured at different conditions (pressure, humidity, stoichiometry, with and without air bleeding, in flow-through and dead-end operation). In flow-through mode, the cell voltage is relatively insensitive to the presence of inert gases (e.g. -20 mV with inerts/H-2 from 0 to 20.10(-2) at 0.3 A/cm(2)), and resistant also to CO (e.g. -35 mV with inerts/H-2 = 20.10(-2) and CO/H-2 from 0 to 20.10(-6) at 0.3 A/cm(2)), thanks to the Ru presence in the anode catalyst. Looking at the current density distribution on the cell surface, the most critical areas are the cathode inlet, likely due to insufficient air humidification, and the anode outlet, because of low hydrogen concentration and CO poisoning of the catalyst. Dead-end operation is also investigated using humid or impure hydrogen. In this case relatively small amount of impurities in the hydrogen feed rapidly reduces the cell voltage, requiring frequent purges (e.g. every 30 s with inerts/H-2 = 0.5.10(-2) at 0.3 A/ cm(2)). These experiments set the basis for the management of the PEMFC stack integrated into the m-CHP system based on the FluidCELL concept. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.