NOVELTY - A pressure producing part comprises electrode leads (I,II) associated with an electrochemically-reacting cell device and electrically connected between the anode and cathode of the device. The device is formed with a movable pressure accepting part containing a portion which accepts pressure changes and which increases in size when actuated and decreases in size when de-actuated.    USE - As pressure producing portion.    ADVANTAGE - The pressure producing portion applies sufficient fluid force and motion through fluid conduits to a piston. Oxidation of hydrogen and reduction of oxygen to water is performed rapidly by short circuiting and is facilitated using the electrodes. The rate of process is controlled by an external electrical circuit.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) A method for operating the electrochemical cell device which involves applying a voltage across the anode and cathode to generate gas and recombining the gas to liquid, by reversing a voltage across the anode and cathode; and    (2) A fuel cell structure (310) comprising catalyst impregnated carbon cloth electrodes (312,314) respectively forming an anode and a cathode. An ionically conducting membrane separates the anode and cathode and forms a membrane electrode assembly. An electrode lead (I) is connected to the anode and an electrode lead (II) is connected to the cathode. A support structure having flexible surfaces and inner surfaces forming a chamber where the membrane electrode assembly is located, is provided. A sealing element seals the membrane electrode assembly and allows the electrodes (312,314) to extend between outside of the support structure and the membrane electrode assembly. The flexible surfaces are expanded and contracted by applying bias.    DESCRIPTION OF DRAWING(S) - The figure shows a rigid walled device used to drive an external device, e.g. a piston.    Housing (299)    Fuel cell (310)    Electrodes (312,314)    Piston (320)