A new study by researchers at UC Santa Cruz has found an efficient and cost-effective way to use aluminum’s reactivity to generate clean hydrogen.
The study shows that an easily produced composite of gallium and aluminum creates aluminum nanoparticles that react rapidly with water at room temperature to produce large amounts of hydrogen. The gallium was easily recovered for reuse after the reaction, which yields 90% of the hydrogen that could theoretically be produced from reaction of all the aluminum in the composite.
Aluminum is a highly reactive metal that can strip oxygen from water molecules to generate hydrogen gas. Its widespread use in products that get wet poses no danger because aluminum instantly reacts with air to acquire a coating of aluminum oxide, which blocks further reactions.
Gallium, a liquid at just above room temperature, removes the passive aluminum oxide coating, allowing direct contact of aluminum with water. The new study includes several novel findings that could lead to practical applications. A U.S. patent application is pending on this technology.
“We don’t need any energy input, and it bubbles hydrogen like crazy. I’ve never seen anything like it,” said UCSC Chemistry Professor Scott Oliver.
Previous studies had mostly used aluminum-rich mixtures of aluminum and gallium, but the research team found an unexpectedly high hydrogen production with a gallium-rich composite. Using scanning electron microscopy and x-ray diffraction, the researchers showed the formation of aluminum nanoparticles in a 3:1 gallium-aluminum composite, which they found to be the optimal ratio for hydrogen production.
“The gallium separates the nanoparticles and keeps them from aggregating into larger particles,” Singaram, professor of chemistry and biochemistry said. Making the composite required nothing more than simple manual mixing.
“Our method uses a small amount of aluminum, which ensures it all dissolves into the majority gallium as discrete nanoparticles,” Oliver said. “This generates a much larger amount of hydrogen, almost complete compared to the theoretical value based on the amount of aluminum. It also makes gallium recovery easier for reuse.”
The composite can be made with readily available sources of aluminum, including used foil or cans, and the composite can be stored for long periods by covering it with cyclohexane to protect it from moisture.
In spite of gallium being not abundant and being relatively expensive, it can be recovered and reused multiple times without losing effectiveness, Singaram said. It remains to be seen, however, if this process can be scaled up to be practical for commercial hydrogen production.
