NOVELTY - An electrochemical stack cell comprises cells, each having a pair of frames (2, 3), which have continuous margins around central voids (12) providing half cell cavities, apertures (17) in the continuous margins providing ducts for flow of electrolyte, electrolyte distribution rebates (24), and passages (18, 23) in the continuous margins for electrolyte flow from one of the duct apertures, into and out of the half cell at the distribution rebates and to another of the duct apertures, where flow passages are formed in the faces of the margins and are closed by abutting opposite frame faces.    USE - The electrochemical stack cell, particularly regenerative reduction/oxidation (redox) fuel cell stack is useful in the generation of electricity.    ADVANTAGE - The flow passages are defined in one rigid frame face, closed by another. Thus, the passages are dimensionally stable, electrically isolated from the plate electrodes and not bounded by the membrane. This arrangement gives more predictable properties to the finished stack e.g. in terms of the loss due to ohmic connection of one electrode to the next by the electrolyte columns in the passages connecting each electrode to its neighbor via the electrolyte flow passages. The O-rings provide a high degree of sealing integrity. The cell thickness, in terms of the separation from the membranes to the electrode plates is independent of the thickness of the frames. The frames can be molded in simple insert-less moulds, and the only additional parts required are the electrodes, membranes, and seals, compared with the prior art, where numerous location washers were required.    DETAILED DESCRIPTION - An electrochemical stack cell comprises cells arranged side-by-side in a stack, each cell having:    (1) a membrane (4);    (2) a first half cell cavity on one side of the membrane and a second half cell cavity on the other side of the membrane;    (3) a respective electrode plate at the side of each half cell opposite from the membrane, each electrode plate providing contact between adjacent cells for intermediate ones of the cells; and    (4) a pair of frames, one for one half cell and the other for the other, the frames captivating the membrane between themselves, locating the electrode plates, and having continuous margins around central voids providing the half cell cavities, apertures in the continuous margins providing ducts for flow of electrolyte through the stack for distribution to the cells, electrolyte distribution rebates at opposite inside edges of the margins, and passages in the continuous margins for electrolyte flow from one of the duct apertures, into and out of the half cell at the distribution rebates and to another of the duct apertures, where each plate electrode is captivated between a frame from one cell and a frame from an adjacent cell with greater than or equal to2 portions of the margins of these frames extending outside respective edges of the plate electrode, the adjacent cell frames having faces, which abut at the portions, the flow passages are formed in the faces of the margins and are closed by abutting opposite frame faces, and through-frame openings are provided in the frames for extending the passages from the abutting faces of the frames to the other, membrane side of the frames into distribution rebates.    DESCRIPTION OF DRAWING(S) - The figure is an exploded view of two frames, an electrode, and a membrane of the cell stack.    Frames (2, 3)    Membrane (4)    Central voids (12)    Apertures (17)    Passages (18, 23)    Electrolyte distribution rebates (24)