A fuel cell stack (10) comprises a plurality of fuel cells each with a chamber (K) for liquid electrolyte with at least one inlet (32) and at least one outlet (34), and at least one header (30) to supply electrolyte to all the cells in parallel. The fuel cell stack (10) comprises multiple elements (62, 63, 64, 70) stacked together, wherein at least some of the elements (62, 63, 64) comprise a plate having a surface that is intended to abut a surface of an adjacent element (70). The plate (62, 63, 64) defines a first surface portion that is to be sealed to the adjacent element, the first surface portion defining a groove with a sealing element of resilient polymeric material (72, 73, 74) moulded into the groove and projecting out of the groove. The plate also defines a second surface portion that is exposed, such that when stacked and compressed together the resilient polymeric material (72, 73, 74) is compressed entirely into the surface groove and seals onto the surface of the adjacent element (70) whereas the second surface portion is in direct contact with the surface of the adjacent element (70). When the stack (10) is compressed, the length of the stack is well-defined. The sealing takes place only where sealing is required, and is more reliable.