A redox fuel cell comprising 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 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.