TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Components: The groove network comprises closed groove segments (28,30,32,34). Each segment comprises groove segment(s) in one of separate mechanism facing and closed by another separate mechanism to form closed groove segments. At least some of said closed groove segments comprise a first groove segment in one of said separate mechanism facing a second groove segment in another of said separate mechanism. The electrochemical cell assembly comprises individual electrochemical cells. Each electrochemical cell comprises separate mechanism including a connection aperture. The connection apertures form a connection duct of the groove network extending through each electrochemical cell. The connection ducts of individual electrochemical cells are interconnected and are connected to filling port(s), thus the groove network extends through electrochemical cells to enable a seal for all of the electrochemical cells to be formed simultaneously The seal has been formed by injection of a liquid elastomeric seal material and subsequent curing of the elastomeric seal material. The assembly includes proton exchange membrane electrochemical cells. The proton exchange member electrochemical cells comprise an anode flow field plate (22), a cathode flow field plate (24), a membrane electrode assembly (26). The membrane electrode assembly includes a proton exchange membrane and located between the anode and cathode flow field plates, a first gas diffusion layer between the anode flow field plate and the membrane electrode assembly and a second gas diffusion layer between the membrane electrode assembly and the cathode flow field plate. The anode and cathode flow field plates define apertures for forming with apertures of other electrochemical cells, ducts for fuel, an oxidant and a coolant. Each anode flow field plate and each cathode flow field plate include recesses to accommodate the first and second gas diffusion layers. The portions of the anode and the cathode flow field plates of each electrochemical cell not separated by the membrane electrode assembly are separated by an insulator, thus compression of the first and second gas diffusion layers is determined by the dimensions of the recesses. The facing surfaces of each pair of anode and cathode flow field plates have flat opposed faces. The gas diffusion layer and membrane extend to edges of the flow field plates. The surfaces of the anode and cathode flow field plates include grooves for the elastomeric seal material that fills the grooves and penetrates the gas diffusion layers to form a seal with the membrane. Each proton exchange membrane includes a peripheral flange. The seal material is bonded to the peripheral flanges. Each flat, opposed face of the anode and cathode flow field plates includes flow field channels for gases. The assembly includes a membrane electrode unit intended for assembly with similar membrane electrode units into a larger electrochemical cell stack. The electrochemical cell assembly includes end surfaces adapted for mating with end surfaces of similar membrane electrode units. The end surface(s) is provided with a seal for forming a seal with the end surface of another similar membrane electrode unit. Each of the anode and cathode flow field plates includes a first fuel aperture, a first coolant aperture and a first oxidant aperture at its first end; and a second fuel aperture, a second coolant aperture and a second oxidant aperture at its other end. Each of the anode and cathode flow field plates includes a first connection aperture at one end and a second connection aperture at other end for supply of material to form seal. The anode flow field plate includes on a rear face away from the membrane electrode assembly, a groove network portion including groove segments that extend around the fuel and oxidant apertures and that extend only partially around the coolant apertures, thus to enable coolant to flow between the coolant apertures across its rear face. A second groove network portion is provided on the front face of the anode flow field plate and includes groove segments extending around at least the oxidant and coolant apertures. The anode flow field plate includes a channel network on its front face to distribute fuel gas over the first gas diffusion layer. The cathode flow field plate includes a third groove network portion on the rear face away from the membrane electrode assembly, and a fourth groove network portion. The third groove includes groove segments that extend around the oxidant and fuel apertures and that extend only partially around the coolant apertures, to enable coolant flow across the rear face between the coolant apertures. The fourth groove network portion on the front face of the cathode flow field plate includes groove segments extending around at least the fuel and coolant apertures. The cathode flow field plate includes a channel network on the front face to distribute oxidant gas over the second gas diffusion layer. Each of the connection apertures is positioned to intersect groove segments around the coolant and fuel apertures. The groove segments are dimensioned and are of a shape and size to provide similar filling times with longer groove segments being provided with larger cross sections to prevent occurrence of air pockets. The assembly includes vents extending between the groove network and exterior(s) of the electrochemical cell assembly and internal chambers within the electrochemical cell assembly. The vents are dimensioned to permit air to escape and are small enough to cause pressure to build up in the elastomeric material to ensure complete filling of the entire groove network. Each mechanism includes at least two connection apertures and vents located equal distance between the connection apertures for venting air during filling of the groove networks.