A redox membrane based flow fuel cell includes a reducing agent solution compartment with an inlet and outlet to supply reducing agent solution and an oxidation agent solution compartment with an inlet and outlet to supply oxidation agent solution. A barrier separating the compartments consists of a water-insoluble synthetic metal polymer membrane lacking any separate electrode on surfaces of the membrane and being exposed directly to the solutions. A current collection electrode is in each of the compartments and is disposed to convert ion- to electron-based currents. The current collection electrodes can be reference electrodes.