NOVELTY - An electrochemical cell stack comprises anode, cathode, and membrane separator frame. The membrane separator frame has a central portion defining a membrane-receiving aperture. Each of anode, cathode, separator frame and end wall has a portion defining an anolyte flow inlet channel, a catholyte flow inlet channel, a spent anolyte channel, and a spent catholyte channel.    USE - For use in electrolytic production of hydrogen and oxygen (claimed).    ADVANTAGE - The inventive electrochemical cell stack eliminates the need for end-boxed and compressible elastomeric materials. It has higher operating temperatures. The drastic reduction in the volume of evolved gas lowers the electrical resistance of the mixture of electrolyte and gas bubbles within the cell compartment to produce higher energy efficiency. The rate of flow of electrolyte required through the cell is much less, thus decreasing the size of the electrolyte channels required, the capacity of the pump, and the erosion and wear on all components of the cell caused by high linear velocity of flowing electrolyte. Less heat is lost from the stack due to the smaller amount of water that is evaporated. The cell stack carries electrolysis at temperature above 100degreesC for greater energy efficiency.    DETAILED DESCRIPTION - An electrochemical cell stack comprises stack walls and electrolytic cells within the stack walls. Each cell comprises an anode (38,48), a cathode (40,46), a membrane (20), a membrane separator frame (14) formed of a nonconductive material and having first and second sides, and impermeable cell end wall. The frame has a frame first planar peripheral surface on the first side, and a frame second planar peripheral surface on the second side. The impermeable cell end wall (12) is formed of a nonconductive material between anode and cathode and the anodes and cathodes of adjacent cells of the stack (10). The frame has a central portion defining a membrane-receiving aperture (18). The membrane is within the aperture to provide an anolyte circulation chamber (22) and a catholyte circulation chamber (23), distinct one from the other, within the frame. Each of the anode, the cathode, the separator frame and the end wall has a portion defining an anolyte flow inlet channel, a catholyte flow inlet channel, a spent anolyte channel and a spent catholyte channel; and where the anolyte flow inlet channel and the spent anolyte channel are in communication with the anolyte circulation chamber, the catholyte flow inlet channel (32) and the spent catholyte channel (34) are in communication with the catholyte circulation chamber within the frame.    DESCRIPTION OF DRAWING(S) - The drawing shows a diagrammatic, exploded perspective view of a monopolar, filter press, four-cell stack, in open form.    Stack (10)    Cell end wall (12)    Membrane separator frame (14)    Membrane-receiving aperture (18)    Membrane (20)    Anolyte circulation chamber (22)    Catholyte circulation chamber (23)    Catholyte flow inlet channel (32)    Spent catholyte channel (34)    Anode (38, 48)    Cathode (40, 46)