Researchers at Purdue University have developed a new aluminum-rich alloy that produces hydrogen by splitting water, and they contend it can be an alternative fuel for transportation and power generation. “We now have an economically viable process for producing hydrogen ondemand for vehicles, electrical generating stations and other applications,” states Jerry Woodall, the distinguished professor of electrical and computer engineering who invented the process.

The new alloy contains 95% aluminum and 5% of a galliumindium- tin alloy. Because the percentage of gallium is significantly less than previous forms of the alloy, hydrogen can be produced less expensively, Woodall states.

When immersed in water, the new alloy splits water molecules into hydrogen and oxygen, which immediately reacts with the aluminum to produce aluminum oxide, or alumina (which can be recycled back into aluminum.) Recycling aluminum from aluminum oxide is less expensive than mining and refining bauxite, so the new new technology is claimed by Woodall to be more competitive with other forms of energy production.

“After recycling both the aluminum oxide back to aluminum and the inert gallium-indium- tin alloy only 60 times, the cost of producing energy both as hydrogen and heat using the technology would be reduced to 10 cents per kilowatt hour, making it competitive with other energy technologies,” Woodall states.

Controlling the microscopic structure of the solid aluminum and the gallium-indium-tin alloy mixture is critical to developing the alloy for large-scale technologies, Woodall explains, “because the mixture tends to resist forming entirely as a homogeneous solid due to the different crystal structures of the elements in the alloy and the low melting point of the gallium-indium-tin alloy.”

The new alloy has two phases, according to the heating method applied to it. “I can form a one-phase melt of liquid aluminum and the gallium-indium-tin alloy by heating it. But, when I cool it down, most of the gallium-indium-tin alloy is not homogeneously incorporated into the solid aluminum, but remains a separate phase of liquid,” Woodall explains. “The constituents separate into two phases just like ice and liquid water.” This two-phase composition is critical because it allows the aluminum alloy to react with water and produce hydrogen.

The Purdue researchers discovered that slow-cooling and fast-cooling the 95/5 aluminum alloy produced drastically different versions. The fast-cooled alloy contains aluminum and the gallium-indium-tin alloy, apparently as a single phase. In order for it to produce hydrogen, it had to be in contact with a puddle of the liquid gallium-indium-tin alloy. “That was a very exciting finding because it showed that the alloy would react with water at room temperature to produce hydrogen until all of the aluminum was used up,” Woodall states.

Next, the engineers discovered that slow-cooling formed a two-phase solid alloy, meaning solid pieces of the 95/5 aluminum alloy react with water to produce hydrogen, eliminating the need for the liquid gallium-indium-tin alloy.

“This technology has exciting potential, and I hope that it receives a fair and detailed evaluation and consideration from the scientific, government, and business communities,” according Jay Gore, the Vincent P. Reilly Professor of Mechanical Engineering and interim director of the Purdue Energy Center, which is partially funding the research.

Slow-cooling has made it possible to create forms of the alloy containing higher concentrations of aluminum. At Purdue, researchers are developing a method to create briquettes that could react with water to produce hydrogen on-demand. Such a technology would eliminate the need to store and transport hydrogen, Woodall said.

The gallium-indium-tin alloy component is inert, which means it can be recovered and reused at almost 100% efficiency. The Hall-Hroult process is used to recycle the aluminum oxide back into aluminum.

The aluminum splits water by reacting with the oxygen, freeing hydrogen in the process. The gallium-indium-tin alloy inhibits aluminum oxidation at the surface by forming a skin.

For the technology to be used in major applications, a large-scale recycling program would be required to turn the alumina back into aluminum and to recover the gallium-indium- tin alloy. Other infrastructure components, such as those related to manufacturing and the supply chain, also would have to be developed, Woodall explains.