NOVELTY - A fuel cell system comprises mixed-reactant fuel cell stack (108); mass/enthalpy exchange module (104) located downstream of fuel cell stack and upstream of fuel injection point, and having inlet(s) (105) for receiving mixed reactant flow exiting fuel cell stack and inlet(s) (113) for receiving flow of oxidant i.e. air or oxygen; a mechanism for delivering a flow of oxidant to the mass/ enthalpy exchange module; a reservoir for liquid fuel i.e. methanol or methanol/water solution; and a mechanism for introducing the liquid fuel into the mixed-reactant flow at the fuel introduction point.    USE - The fuel cell system is used for generating electrochemical power.    ADVANTAGE - The fuel cell system achieves a simplified balance of plant due to a methanol/water recovery system based on mass/enthalpy exchange between the reactant flow exiting the fuel cell stack and flow entering the fuel cell stack. The mass/enthalpy exchange module recycles un-reacted fuel, water, and heat from the stack exhaust to incoming fresh oxidant.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (1) a method of recycling mixed-reactant fuel comprising passing an oxidant flow stream through a mass/enthalpy exchange module; passing a mixed-reactant fuel cell stack exhaust flow stream through the mass/enthalpy exchange module; transferring un-reacted fuel, water, and heat in the fuel cell stack exhaust flow stream to the oxidant flow steam; and producing recycled mixed-reactant fuel; and    (2) a method of generating electrochemical power comprising adding liquid fuel to recycled mixed-reactant fuel to produce reconstituted mixed-reactant fuel; passing the reconstituted mixed-reactant fuel through a mixed-reactant fuel cell stack; and generating electrochemical energy.    DESCRIPTION OF DRAWING(S) - The figure is a schematic diagram of a recycling mixed-reactant fuel cell system with vapor recovery.    Mass/enthalpy exchange module (104)    Inlet for mixed reactant flow (105)    Mixed-reactant fuel cell stack (108)    Inlet for oxidant flow (113)    Oxidant source (124)