In experiments, biofuel cells have harnessed membranes of living bacteria to separate anode from cathode--enabling them to share an electrolyte chamber like a lead-acid battery. Now, researchers at the Pacific Northwest National Laboratory have purified the essential protein performing a fuel-cell membrane's electronic function, clearing the way to commercialize biofuel cells sans bacteria. The team purified the bacterium down to the essential protein in the cell wall--eliminating the need to keep the bacterium alive. The only missing element was a fuel source, which biomass could supply, lab scientists reasoned. Now they propose biofuel cell arrays to harvest biomass in tiny reactors. The reaction creates a mobile electron carrier that shuttles electrons to the protein-coated electrodes, generating electricity as it neutralizes the biomass. The proposed biofuel cells would use a cheap porous hematite electrode in which the bacteria's purified protein could be bound. The coated electrodes would catalyze the reaction, enabling electricity to flow from the anode to the cathode using nothing more than the biological agents in the biomass as fuel.