Purdue Researchers Refine Aluminum-Gallium Alloy for On-Board Hydrogen Production; May Meet DOE 2010 Target of 6% Hydrogen Mass Density
|Aluminum-Gallium (Al-Ga) phase diagram. The “Ga-rich liquid” refers to Prof. Woodall’s 1982 patent. (Below) Click to enlarge.|
Researchers at Purdue University have further developed their technology, announced earlier this year, for cost-effective hydrogen production via the splitting of water with an aluminum-gallium alloy.
Aluminum reacts vigorously with water to produce hydrogen, alumina (aluminum oxide, Al2O3) and heat in the reaction:
2Al + 3H2O → 3H2 + Al2O3 + heat
This basic property has lured numerous researchers interested in generating hydrogen from the aluminum-water reaction for modern transportation systems for at least 35 years.
A 1972 paper by I.E. Smith from Cranfield Institute of Technology summarized past efforts and proposed a mechanism for “Hydrogen generation by means of the aluminum/water reaction”.
However, air-exposed aluminum forms a passivating skin of alumina that protects it from further rapid oxidation. A viable aluminum-water hydrogen system must overcome the protective layer to allow the reaction to continue, while still meeting the other constraints for on-board hydrogen storage or generation. A number of efforts over the past decades have explored the potential of developing an amalgamated aluminum surface that can sustain the reaction with water.
The basic approach taken by Purdue professor Jerry Woodall, the inventor of this aluminum-gallium process, is to disrupt the passivating oxide skin with the gallium component of the alloy.
The gallium component is inert, which means it can be recovered and reused.
This is especially important because of the currently much higher cost of gallium compared with aluminum. Because gallium can be recovered, this makes the process economically viable and more attractive for large-scale use. Also, since the gallium can be of low purity, the cost of impure gallium is ultimately expected to be many times lower than the high-purity gallium used in the electronics industry.
The aluminum oxide product of the reaction can be recycled back into aluminum. The recycled aluminum would be less expensive than mining the metal, making the technology more competitive with other forms of energy production, Woodall said.
The Purdue researchers are developing a method to create particles of the alloy that could be placed in a tank to react with water and produce hydrogen on demand. Since the technology was first announced in May, researchers have developed an improved form of the alloy that contains a higher concentration of aluminum.
In recent research, the engineers rapidly cooled the molten alloy to make particles that were 28% aluminum by weight and 72% gallium by weight. The result was a metal stable solid alloy—able to be handled like a solid, rather than a liquid—that also readily reacted with water to form hydrogen, alumina and heat, Woodall said.
Following up on that work, the researchers discovered that slowly cooling the molten alloy produced particles that contain 80% aluminum and 20% gallium.
Particles made with this 80-20 alloy have good stability in dry air and react rapidly with water to form hydrogen. This alloy is under intense investigation, and, in our opinion, it can be developed into a commercially viable material for splitting water.—Jerry Woodall
Assuming 50% of the water produced as waste is recovered and cycled back into the reaction, the new 80-20 alloy has a hydrogen mass density greater than 6%, which meets the DOE’s 2010 goal.
Recent findings are detailed in the first research paper about the work, which will be presented on 7 Sep during the 2nd Energy Nanotechnology International Conference in Santa Clara, Calif. The paper was written by Woodall, Charles Allen and Jeffrey Ziebarth, both doctoral students in Purdue’s School of Electrical and Computer Engineering.
Aluminum is refined from the raw mineral bauxite, which also contains gallium. Producing aluminum from bauxite results in waste gallium.
The researchers note in the paper that for the technology to be used to operate cars and trucks, a large-scale recycling program would be required to turn the alumina back into aluminum and to recover the gallium.
The Purdue researchers had thought that making the process competitive with conventional energy sources would require that the alumina be recycled back into aluminum using a dedicated infrastructure, such as a nuclear power plant or wind generators. However, the researchers now conclude that recycling the alumina would cost far less than they originally estimated, using standard processing already available.
Since standard industrial technology could be used to recycle our nearly pure alumina back to aluminum at 20 cents per pound, this technology would be competitive with gasoline. Using aluminum, it would cost $70 at wholesale prices to take a 350-mile trip with a mid-size car equipped with a standard internal combustion engine. That compares with $66 for gasoline at $3.30 per gallon. If we used a 50 percent efficient fuel cell, taking the same trip using aluminum would cost $28.—Jerry Woodall
The Purdue Research Foundation holds title to the primary patent, which has been filed with the US Patent and Trademark Office and is pending. An Indiana startup company, AlGalCo LLC., has received a license for the exclusive right to commercialize the process.
In 1967, while working as a researcher at IBM, Woodall discovered that liquid alloys of aluminum and gallium spontaneously produce hydrogen if mixed with water. The research, which focused on developing new semiconductors for computers and electronics, led to advances in optical-fiber communications and light-emitting diodes, making them practical for everything from DVD players to television remote controls and new types of lighting displays. That work also led to development of advanced transistors for cell phones and components in solar cells powering space modules like those used on the Mars rover, earning Woodall the 2001 National Medal of Technology from President George W. Bush.
Also while at IBM, Woodall and research engineer Jerome Cuomo were issued a US patent in 1982 for a solid state, renewable energy supply. The patent described their discovery that when aluminum is dissolved in liquid gallium just above room temperature, the liquid alloy readily reacts with water to form hydrogen, alumina and heat.
Future research will include work to further perfect the solid alloy and develop systems for the controlled delivery of hydrogen.
The 2nd Energy Nanotechnology International Conference is sponsored by the American Society of Mechanical Engineers and ASME Nanotechnology Institute.
Jerry M. Woodall, Jeffrey Ziebarth, Charles R. Allen; ”The Science and Technology of Aluminum-Gallium Alloys as a Material for Energy Storage, Transport and Splitting Water“ (ENIC2007-45014, Proceedings of 2nd Energy Nanotechnology International Conference)
I.E. Smith, “Hydrogen generation by means of the aluminum/water reaction”; Journal of Hydronautics, 1972, 0022-1716 vol.6 no.2 (106-109)