Portland, Ore. Biofuel cells can harness the membranes of living bacteria to separate the anode from the cathode, enabling them to share the same electrolyte chamber, like a lead-acid battery. To date, however, such cells have only been experimental, since the bacteria have to be kept alive inside the fuel cell. Now researchers at the Pacific Northwest National Laboratory (PNNL) have purified the essential protein that performs the electronic function of a fuel-cell chamber membrane, clearing the way to commercializing biofuel cells sans bacteria.
"We believe this is the first time that anyone has been able to isolate a bacteria protein and use it to transfer electrons to a mineral without the rest of the cell," said Thomas Squier, senior author and lab fellow at PNNL. "We hypothesize that you could coat the electrodes of biofuel cells with our proteins and generate electricity from a biomass."
Biofuel cells are on PNNL's list of next-generation energy-producing technologies to meet President Bush's Energy Initiative goal of reducing U.S. dependence on foreign oil 75 percent by 2025. But it was during work on a bioremediation project (where bacteria were being cultured to coat toxic spills of heavy metals to prevent the metals' seeping into groundwater) that one group discovered a class of bacteria whose metabolism required the organism to transport electrons across its cell membrane, potentially enabling biofuel cells using living bacteria.
"We are working with a class of organism that is unique in its ability to shuttle quadrillions of electrons outside of itself to minerals as a part of its basic metabolism," said Squier.
At first the biofuel cell experiments followed the lines of similar work elsewhere, but then Squier's team got a whiff of the living biofuel cell work. Working with the Shewanella oneidensis bacterium, the team perfected a method of purifying the organism down to the essential protein in the cell wall that transports electrons, thereby eliminating the need to keep the bacterium alive.
"Our hope is that with our purified proteins, we might be able to make more stable biofuel cells structurally, so they can last longer," said Squier.
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.