TECHNOLOGY FOCUS - BIOTECHNOLOGY - Preferred Component: The metal-oxidizing microorganisms are Acidithiobacillus genus (such as A. ferrooxidanss); Leptospirillum genus (such as L. ferrooxidans, L. ferriphilum or L. ferrodiazotrophum); Ferroplasma genus, Acidimicrobium, Alicyclobacillus, and/or Sulfobacillus. The metal-oxidizing microorganisms include microbial mixtures of autotrophic organisms such Leptospirillum with mixotrophic microorganisms such as Ferroplasma.    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Component: The redox couple is ferrous ion/ferric ion (Fe2+/Fe3+), cuprous ion/cupric ion (Cu+/Cu2+) or molybdenum (Mo5+/Mo6+). The reaction at the cathode electrode is reduction of Fe3+ in a reaction given by 4Fe3+ + 4e- = 4Fe2+, and Fe2+ are oxidized by metal-oxidizing (preferably iron-oxidizing) microorganisms to Fe3+ in an aerobic oxidation reaction given by 4Fe2+ + 4H+ + O2 = 4Fe3+ +2H2O. The proton conducting membrane, which can be a proton exchange membrane, is non-permeable to ions having a higher-valence than protons (H+). The proton conducting membrane is made of inert fibrous material having pores with size selected to inhibit catholyte flow through and in the membrane. The anode includes a hydrophobic constituent. The catholyte includes dissolved nutrients for facilitating growth of the metal-oxidizing microorganisms. The dissolved nutrients include ammonium, potassium, magnesium, calcium, sulfate, nitrate, phosphate and/or chloride ion. The fuel having a hydrogen constituent is hydrogen gas (H2). The electrochemical oxidation reaction is oxidation of H2 at the anode electrode in a reaction given by 2H2 = 4H+ + 4e-, so that an overall biofuel cell reaction is given by 2H2 + O2 = 2H20. The anode electrode is made from a non-platinum catalyst represented by a transition metal compound consisting of tungsten carbide, iron phosphide, or cobalt phosphide. The cathode electrode includes a layer of a porous material having structure and composition consisting of woven carbon-based fibrous material made of graphite or activated carbon, non-woven fibrous material made of carbon, graphite or activated carbon fibers, sponge-type materials made of graphite, activated carbon or glassy carbon, composite carbon-based material made by attaching powder or fibers, made of carbon, activated carbon, graphite, and/or graphitized activated carbon on a conductive support, containing two sub-two layers with a first sub-layer containing a hydrophobic material and a second upper layer being hydrophilic, a composite material formed on an external surface of the proton-exchange membrane and mounted in the vessel facing the liquid in the vessel, or carbon black. The cathode electrode includes additives consisting of activated carbon powder or carbon black. The fluid containing O2 fed into the bioreactor includes carbon dioxide (CO2) for production of biomass. The chemically inert material is silicon dioxide powder or gel, aluminum oxide (alumina), jarosite or calcium sulfate.    TECHNOLOGY FOCUS - METALLURGY - Preferred Component: The anode electrode can be other metals of the platinum group. The porous material can be stainless steel. The conductive support is a stainless-steel mesh. The additives also consist of lead, gold, platinum or palladium.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Material: The fuel having hydrogen constituent is hydrogen gas, methanol, ethanol, ammonia or hydrazine. The anode electrode is platinized carbon.    TECHNOLOGY FOCUS - POLYMERS - Preferred Material: The hydrophobic material is Teflon(RTM: PTFE).