NOVELTY - A chamber is separated by a polymer membrane (1) into two flow-through compartments where each compartment has a current collecting electrode (2, 3) of a predetermined kind. The membrane is made of a synthetic metal polymer, in which one compartment has a solution of reducing and another compartment has a solution of oxidizing agent, respectively. The membrane is made of polyaniline, polypyrrole or polythiophene or their derivatives so that the polymer is in electroconductive state.    USE - Redox membrane-based flow fuel cell for use as electrochemical energy source for generating electric energy.    ADVANTAGE - The redox membrane-based flow fuel cell is featured with low cost, modularity, flexible operation, possibility to use sea water with dissolved sodium chloride and to discharge solutions completely for maintenance without damaging the electrochemical cells. The transmembrane voltage of practically important magnitude can be generated to use it in an electrochemical system with low electric resistance as an efficient electric power source. The redox fuel cell electric voltage is generated directly on a membrane and platinum (Pt) electrodes are not necessary. Instead of oxygen or air it is possible to use different oxidants in flowing aqueous solutions without their preliminary conversion to oxygen. Reducing agents on another side of the membrane also can be delivered as an aqueous solution, thus providing the ability to mechanically replenish both the oxidant and the fuel source and to meet power and energy requirements. The membrane is stable enough, so that it is possible to use an oxidant and reducing agent in amounts equivalent to much more than usual amount in a closed battery. Utilization of the reactants can be further increased if the solutions are flowing in a battery from one membrane-based flow fuel cell to another. Initial oxidant and reducing agents can be stored in a stable and save solid form, thus making the system attractable based both on a total system weight and volume. Synthetic metals can be reduced by very many different reducing chemicals, thus eliminating the need to use hydrocarbons as a fuel. The reversible redox reactants can be used, so that the electrochemical system becomes rechargeable. An external source of electrochemical energy for example, from power stations during night time, can be used to recover the initial reactants, and then the chemicals can be reused in a daytime when the energy demand is higher. The fuel cell system is very volume and energy efficient. The ancillary equipment to operate the device is a simple pump with two channels to supply solutions of reducing and oxidizing agent. Energy necessary is much less, which leads to high energy conversion efficiency. The total energy delivered by a flow fuel cell system is limited only by the amount of redox agent and oxidant available.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic diagram of the redox membrane-based flow fuel cell.    Polymer membrane (1)    Current-collecting electrodes (2, 3)    Inlets and outlets (4-7)