NOVELTY - Fuel cell bioreactor (10) comprises a vessel having metal-oxidizing microorganisms and catholyte; a cathode electrode (18) immersed in catholyte; and an anode electrode assembly (15) including a membrane anode assembly (20) which includes a proton conducting membrane attached to anode electrode (26). A reaction at cathode electrode is reduction of first component of redox couple in higher oxidation state to second component in lower oxidation state. The second component is oxidized back to first component by metal-oxidizing microorganisms in aerobic oxidation reaction with oxygen.    USE - For generating electricity.    ADVANTAGE - A small amount of energy is consumed due to the absence of liquid pumps. A high cathode potential may be used because of the direct contact of cathode with ferric ions, produced by the microorganisms, and also due to the high liquid recirculation rate. The design bioreactor allows for very easy, non-intrusive servicing of the anode electrode assemblies and the cathodes. This is due to the fact that both the anode and the cathode may be freely inserted in the bioreactor and can be easily withdrawn for servicing. The microorganisms may spontaneously grow and become immobilized on the surface of the cathode which will act to additionally increase the cathodic potential by directly supplying the cathode with ferric ions. The economy and environmental effect of fuel cell operation are improved due to increase in current efficiency; elimination of the use of platinum at the cathode; lower cost of current fuel cells; removal of CO2 from atmosphere; and production of potentially highly useful biomass in the form of single cell protein.    DETAILED DESCRIPTION - A fuel cell bioreactor comprises a vessel containing metal-oxidizing microorganisms and a catholyte containing a redox couple with a first component of the redox couple in a higher oxidation state than a second component of the redox couple; a cathode electrode immersed in catholyte; an anode electrode assembly including a membrane anode assembly which includes a proton conducting membrane attached to an anode electrode; and a first fluid feed mechanism for feeding a fluid containing oxygen (O2) and carbon dioxide into the catholyte. The anode electrode assembly includes a current collector physically contacting the anode electrode, where the current collector and the anode electrode are configured to form anode compartment (16) in-between; and an insulating housing (12) into which the current collector and the anode electrode are inserted to seal the anode electrode and the current collector from the catholyte such that the anode electrode assembly is configured so that the anode compartment is separated from the catholyte by the proton conducting membrane. A second fluid feed mechanism is provided for feeding a fuel containing a hydrogen constituent into an anode compartment. A reaction at the cathode electrode is reduction of the first component of the redox couple in a higher oxidation state to the second component in a lower oxidation state. A reaction at the anode electrode is electrochemical oxidation of the fuel to produce electrons (e-) and protons (H+), where protons (H+) cross the proton conducting membrane from the anode compartment into the catholyte. The second component of the redox couple in the lower oxidation state is oxidized back to the first component in the higher oxidation state by metal-oxidizing microorganisms in an aerobic oxidation reaction in the presence of oxygen, where electrical power is obtained by making electrical connection between a load and the anode and cathode electrodes. A liquid circulation mechanism is configured to circulate the catholyte such that the second component of redox couple in the lower oxidation state produced at the cathode and protons (H+) are transported away from the cathode electrode. An INDEPENDENT CLAIM is included for a method for generating electricity.    DESCRIPTION OF DRAWING(S) - The figure shows a diagrammatic representation of a fuel cell bioreactor.    Fuel cell bioreactor (10)    Housing (12)    Anode electrode assembly (15)    Anode compartment (16)    Cathode electrode (18)    Membrane anode assembly (20)    Anode electrode (26)