Hydrogen peroxide could power fuel cell

In the fuel cells, hydrogen peroxide serves two roles: it is a "catholyte," meaning it is both the electrolyte - a liquid that conducts electricity and allows the reaction to occur - and the cathode, or the portion of the battery that attracts electrons. The aluminum serves as the cell's fuel and its anode: as it oxidizes, it gives up electrons. Waste products include water and recyclable chemical compounds. Serendipity has helped the Purdue researchers overcome a major obstacle in the fuel cell work. Earlier attempts by the US Navy to develop the cells were abandoned because the reaction with aluminum quickly formed a thick sludge that hindered the flow of electricity. Because the Purdue engineers didn't have pure aluminum for their work, however, they used an aluminum alloy. To their surprise, and delight, they found that the alloy did not form the sludge.

Aluminum was chosen originally because it is an abundant natural resource and is readily available from recycled sources, says Rusek, who estimates that the cells are at least 20 times higher in energy density than a standard lead-acid car battery. "That means a 20kg lead-acid battery would put out the same amount of energy as a 1kg hydrogen peroxide fuel cell," he says, noting that other metals, such as lithium alloys, might also work.

Rocket fuel
Hydrogen peroxide differs from water only in that it contains two oxygen atoms. It is relatively easy to manufacture - in principle it could be made from water - and it is far less dangerous or expensive than conventional oxidisers such as liquid oxygen. "It is actively being studied together with new types of non-toxic propellants made from alcohol that offer promise as alternatives to the conventional petroleum-based rocket fuels," Rusek says. Engineers hope to have hydrogen peroxide-based rockets in operation within a decade.

Unlike the hydrogen peroxide that is found in chemists, which is about 97% water, the rocket-propulsion variety has just the opposite concentration - 3% water and 97% hydrogen peroxide - and has had critical contaminants removed. This purified, concentrated form of H2O2 is then broken down with chemical catalysts, yielding oxygen that combusts with alcohol-based fuels, such as methanol or ethanol, which can be derived from corn. Such a propulsion system would provide an alternative to today's non-renewable hydrocarbon fuels that are processed from crude oil.