TECHNOLOGY FOCUS - BIOLOGY - Preferred Components: (B) is a hydrogenase from: a bacterium of the genus such as Ralstonia (preferred), Alcaligenes, Aquifex, Azotobacter, Bradyrhizobium, Burkholderia, Chromobactrium, Dechloromonas, Hydrogeneovibrio, Magnetococcus, Magnetosprillum, Microbulhifer, Paracoccus, Pseudomonas, Rhizobium, Rhodobacter, Rubrivivax, Streptomyces, Wautersia or Hydrogenomonas; and Ralstonia eutropha or Ralstonia metallidurans. The Ralstonia eutropha comprising the protein HoxK containing fully defined 360 amino acid sequence of SEQ ID NO:2 and HoxG containing fully defined 618 amino acid sequence of SEQ ID NO:4. (B) is: a fragment of variant of the hydrogenase from Ralstonia eutropha; a membrane bound or a membrane-associated hydrogenase; and a carbon monoxide tolerant.    TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Method: At least a part of the surface of the anode comprises carbon. In the method (B) is in direct electronic contact with the anode. (I) is operated in the substantial absence of an electron mediator. The potential of the anode is maintained at -400mV or greater (preferably 0 to +300mV). (I) comprises a cathode having a cathode catalyst adsorbed, where the catalyst comprises an oxidase enzyme. A membrane does not separate the anode and cathode. In (II), at least a part of the surface of the electrode comprises carbon. EXAMPLE - Electrode coated with the membrane bound hydrogenase from Ralstonia eutropha was prepared by dropping 1microns of Ralstonia eutropha (1micrograms) hydrogenase onto a pyrolytic graphite edge surface which had been previously polished with an aqueous slurry of 1microns alumina. The reaction was performed on a thermostatted electrochemical cell maintained at 45degreesC. The cell solution was a mixed aqueous buffer. The cell comprised gas inlet and outlet fittings and a septum for injecting liquid into the cell solution. The working electrode was clamped tightly onto an electrode rotator unit and was rotated at 2500 rpm. The cell was operated by supplying hydrogen at 103 Pa and at potential of -558mV was applied. The potential was stepped to +142mv. The current recorded, the initial peak settling to a value of 1.8-2 microamperes.