WEST LAFAYETTE, Ind. – Researchers are developing a new type of environmentally friendly fuel cell that runs on aluminum and renewable resources and generates about 20 times more electricity per pound than car batteries.
The cell produces electricity through chemical reactions between hydrogen peroxide and aluminum. If perfected, such an electricity source could one day replace conventional batteries in many applications, including portable electronic equipment.
"It has a huge amount of energy potential," says John Rusek, an assistant professor of aeronautics and astronautics at Purdue University, who is working with students to develop the cell. A poster paper about the research was presented in November, during the Second International Hydrogen Peroxide Propulsion Conference at Purdue.
Hydrogen peroxide, or H2O2, also offers promise in developing low-cost, nontoxic rocket fuels. The chemical 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 "oxidizers," such as liquid oxygen, which are needed to burn rocket fuels.
"It is actively being studied together with new types of nontoxic 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. But at least one visionary couldn't wait that long. Richard Brown, a British engineer, became the fastest man on two wheels in September, when his Gillette Mach 3 Challenger rocket-powered motorcycle hit 365 miles per hour at the Bonneville Salt Flats.
"All I can say is the G force is absolutely obscene," Brown, 34, told researchers during the hydrogen peroxide conference. The 26-foot-long vehicle was powered by rockets that used hydrogen peroxide as an oxidizer.
Unlike the hydrogen peroxide that is found in drugstores, which is about 97 percent water, the rocket-propulsion variety has just the opposite concentration – 3 percent water and 97 percent hydrogen peroxide – and it has had critical contaminants removed, says Stephen Heister, a professor of aeronautics and astronautics at Purdue.
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 nonrenewable hydrocarbon fuels that are processed from crude oil, Heister says.
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 it is 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 U.S. Navy to develop the cells were abandoned because the reaction with aluminum quickly formed a thick sludge that hindered the flow of electricity. However, because the Purdue engineers didn't have pure aluminum for their work, they used an aluminum alloy. To their surprise, they found that the alloy did not form the sludge, Rusek says.
One problem with the experimental cells is that, unlike batteries, they do not immediately provide a steady supply of electricity; it takes about two hours for the cells to reach their peak electrical output before producing a steady current flow, says engineering student Kok Hong Lim, a junior from Singapore who is majoring in aeronautics and astronautics.
Future work will include research aimed at correcting that problem, he says.
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 20-kilogram lead-acid battery would put out the same amount of energy as a one-kilogram hydrogen peroxide fuel cell," he says, noting that other metals, such as lithium alloys, might also work in hydrogen peroxide fuel cells.
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