ALBUQUERQUE, N.M. — The bio-microfuel cell being developed by researchers at Sandia National Laboratories works similarly to a battery. The main difference is that a battery is a “closed” system; its lifetime is fixed by the amount of reactants packaged inside it. The fuel cell is an “open” system, which means that its fuel is supplied on a semi-continuous basis and can be renewed by changing or refilling the fuel tank. By tapping into a plant or animal, the bio-microfuel cell seeks to incorporate a “fuel tank” that refills itself.
The heart of the fuel cell is made up of the anode/proton exchange membrane/cathode stack. Fuel oxidation and oxygen reduction take place at the anode and cathode respectively with the aid of catalysts incorporated into the electrodes to facilitate the reactions.
The proton exchange membrane separates the oxidation and reduction reactions and allows using the electrons released at the anode during the oxidation reaction in an external circuit, while the protons are transported through the membrane to complete the circuit inside the fuel cell. Electrons are received back again from the external circuit at the cathode, where they react with the protons and oxygen atoms to produce water.
In the case of the bio-microfuel cell, the fuel is glucose. When a glucose molecule comes in contact with the catalyst, it splits into two by-product molecules, releasing two protons and two electrons. Sandia researchers are looking at using two different types of catalysts for oxidizing glucose — one made of the enzyme glucose oxidase and one made of a precious metal, such as platinum or an alloy of it.
The researchers would also like to develop catalysts that would allow harvesting more protons and electrons from the by-products produced in the first oxidation reaction. In principle, one should be able to harvest 24 electrons from glucose by using the appropriate catalysts.