NOVELTY - Redox fuel cell comprises: an anode and a cathode (3) separated by an ion selective polymer electrolyte membrane (2); means for supplying a fuel to the anode region of the cell; means for supplying an oxidant to the cathode region of the cell; means for providing an electrical circuit between the anode and the cathode; and a non-volatile catholyte solution flowing fluid communication with the cathode.    USE - (I) is useful in microcells for electronic and portable electronic components and in larger fuel cells for the automotive industry and for stationary and other portable applications such as automotive and portable electronics technology.    ADVANTAGE - (I): has improved catholyte solution and increased cell potential, by maintaining the potential due to a pH drop between the anode and catholyte solution; improves the cell performance by decreasing the membrane resistance; avoids the use of expensive cathodic materials; produces a higher sustainable current; avoids the contamination of the membrane; and utilizes the environmentally friendly materials.    DETAILED DESCRIPTION - Redox fuel cell comprises: an anode and a cathode (3) separated by an ion selective polymer electrolyte membrane (2); means for supplying a fuel to the anode region of the cell; means for supplying an oxidant to the cathode region of the cell; means for providing an electrical circuit between the anode and the cathode; and a non-volatile catholyte solution flowing fluid communication with the cathode, where: the catholyte solution comprises a polyoxometallate redox couple being at least partially reduced at the cathode in operation of the cell, and at least partially re-generated by reaction with the oxidant after such reduction at the cathode; the catholyte solution comprises at least one counterion for the polyoxometallate redox couple; and the counterion comprises one or more divalent ions. An INDEPENDENT CLAIM is included for the catholyte solution for use in (I) comprising the polyoxometallate and the counterion comprising one or more divalent ions.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic diagram of the cathode compartment of a fuel cell.    Polymer electrolyte membrane (2)    Cathode (3)    Cathode gas reaction chamber (5)    Catholyte reservoir (7)    Cathode inlet channel. (8)