A bipolar unit comprising a pair of metal plates, at least one of which is corrugated, fixed by continuous and hydraulically impervious connections, and provided on the external surfaces thereof with porous electric current collectors suitable for the distribution of the gaseous reactants, the collector facing the plate corrugations is interpenetrated therein, thereby achieving a continuous contact and two bipolar units of the invention and one interposed MEA element being assembled to form an elementary fuel cell with an improved electric current distribution and the channels formed between the mutually contacting surfaces of the plate pair by the corrugations of at least one of the plates of each bipolar unit, are crossed by a coolant allowing to optimally adjust the cell operative temperature.