TECHNOLOGY FOCUS - MECHANICAL ENGINEERING - Preferred Module: The sealing element (25) comprises 3 sealing beads stuck together i.e. (25a) which fills the groove on plate (7a) facing the cathode (3) and seals the interface, (25b) which performs a similar function on the anode (2') and (25c) which fills the complementary grooves (22a, 22b) and encompasses the gap (27) between the cooling surfaces. Grooves (26a) and (22a) are connected by holes (29a) though plate (7a), and grooves (26b) and (22b) are connected by holes through plate (7b), these holes being filled with sealing material which bonds the 3 beads together to form an integral element (25) penetrating both pole plates. Alternatively, the injection moulded element (25) encompasses the faces of the pole plates and thus binds the bead (25c) with the beads (25a) and (25b), or the bead (25c) is bound to (25a) and (25b) both by means of the filled holes (29a, 29b) and by means of the sealing material round the pole plates. The cooling surfaces of both pole plates are provided with coolant distribution channels (19a, 19b). The surfaces of the pole plates facing the electrodes may be provided with reaction medium structures (13, 12) enclosed by sealing beads (25a, 25b), or these surfaces may have no such structures, in which case they are combined with electrodes (3, 2') having such structures (13, 12') on the sides facing the pole plates. One of the cooling surfaces of the pole plates has a recess (30) for the compressible element (28), the depth of (30) being such that (28) projects far enough above the recess to compensate for the cooling-induced shrinkage of the sealing material in the grooves (22a, 22b).    TECHNOLOGY FOCUS - POLYMERS - Preferred Materials: Sealing element (25) consists of thermoplastic elastomer, thermoplastic polyurethane or liquid silicone rubber. The conductive, compressible element (28) consists of flexible graphite foil or a non-woven fabric, felt, paper or woven fabric made of carbon or graphite fibres.