The basic module has a large functional surface area compared with its relatively small global surface area.It is composed mainly of a multitude of micro-volumes (10, 110) installed in a closed space between a lower border (1), upper border (2) and side border (3). Each micro-volume wall is covered with a layer forming the membrane/electrodes basic element. Circulation of a first reactant to pass inside each micro-volume (10, 110) is enabled, whereas circulation of a second reactant to pass inside each micro-volume (10, 110) is enabled. The space between the micro-volumes (10, 110) may possibly be filled in with a porous material to stiffen the assembly.Applications for small sized fuel cells.