NOVELTY - A redox fuel cell comprises: an anode and a cathode separated by an ion selective polymer electrolyte membrane; 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 respective anodes and cathodes of the cell; a catholyte solution comprising at least one catholyte component; and a regeneration zone comprising a catholyte channel and a porous member having an active surface.    USE - The redox fuel cell is used in a combined heat and power system, a vehicle, an electronic component, and a catholyte regeneration system; for the combined generation of heat and power; for providing motive power to a vehicle; and for generating power in an electronic component (claimed).    ADVANTAGE - The redox fuel cell is highly improved and can be effectively used for efficient oxidation of redox couples.    DETAILED DESCRIPTION - A redox fuel cell comprises: an anode and a cathode separated by an ion selective polymer electrolyte membrane; 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 respective anodes and cathodes of the cell; a catholyte solution comprising at least one catholyte component, the catholyte solution comprising a redox mediator couple; and a regeneration zone comprising a catholyte channel and a porous member having an active surface, the catholyte channel being arranged to direct a flow of catholyte solution adjacent to or towards the active surface, the means for supplying an oxidant to the cell being adapted to supply the oxidant to the porous member. INDEPENDENT CLAIMS are:    (1) a process for operating a redox fuel cell comprising: providing an anode and a cathode separated by an ion selective polymer electrolyte membrane; providing a catholyte solution comprising at least one catholyte component, the catholyte solution comprising a redox mediator couple; providing a regeneration zone comprising a catholyte channel and a porous member having an active surface; directing a flow of catholyte solution adjacent to or towards the active surface by means of the catholyte channel; supplying an oxidant to the porous member of the regeneration zone; supplying a fuel to the anode region of the cell; and providing an electrical circuit between respective anodes and cathodes of the cell;    (2) a combined heat and power system comprising at least one fuel cell;    (3) a vehicle comprising at least one fuel cell;    (4) an electronic component comprising at least one fuel cell; and    (5) a catholyte regeneration system comprising: a chamber; a first inlet port for receiving into the chamber reduced redox mediator couple from the cathode region of the cell; a first outlet port for supplying oxidized redox mediator couple to the cathode region of the cell; a second inlet port for receiving a supply of oxidant; and a second outlet port for venting gas, water vapor and/or heat from the chamber, a catholyte channel in fluid communication with the first inlet port, a porous member having an active surface, the catholyte channel being arranged to direct a flow of catholyte adjacent to or towards the active surface, where: (a) the porous member comprises pores having an average diameter of 5-100 microns; (b) at least a portion of the active surface is formed of or coated with hydrophilic material; and/or (c) at least a portion of the porous member, excluding the active surface, is formed of a hydrophobic material.