Scientists at the U.S. Department of Energy’s Ames Laboratory, in collaboration with several partners, have discovered a less-expensive, more energy-efficient way to produce ‘Alane’, the shorthand version of the chemical aluminum trihydride. Alane is a hydrogen source that has been widely considered to be a technological dead-end for use in automotive vehicles.
Here was the problem – Alane had earned its dead-end reputation for use in cars because making it from the elements, aluminum and hydrogen, at equilibrium requires the hydrogen gas at about 150,000 PSI pressure for processing. Getting to 150,000 PSI is an energy intensive and containment problem.
The Ames researchers found that atomic-level defects, when present on the surface of aluminum together with hydrogen and titanium, created the conditions necessary for a chemical reaction producing alane to occur, and without the need for hydrogen at tremendously high pressure. While not ready for mainstream synthesis, this work serves as proof of concept of a more efficient and less costly way of producing alane.
Vitalij Pecharsky, Ames Laboratory Scientist and Iowa State University’s Anson Marston Distinguished Professor of Materials Science explains the situation, “Alane is great because it meets all of the criteria put forth by the Department of Energy for hydrogen fuel cell vehicles for energy capacity, weight, system temperature, and cost. Aluminum is cheap, hydrogen is abundant. There’s just one problem: you can’t make it easily. For the longest time it’s been considered impossible to use for vehicle applications because of the extreme difficulties in producing it.”
Researchers paired the predictive advantages of computational analysis with physical experimentation to tackle the applied materials challenge. Along with titanium catalyst dopants and hydrogen, theorists looked at vacancy defects, or missing aluminum, on the surface of aluminum powders and established that this combination working in concert is critical to the low-energy formation of alane. Because such defects can be produced by ball milling to break up mechanically the atomic structure of the metal, experimentalists ball-milled aluminum powders in combination with hydrogen and titanium, and they confirmed the prediction by producing AlH3, or alane. The process used significantly less pressure, only about 5,000 PSI (or 30 times less pressure), to create alane than that needed for equilibrium methods.
Duane Johnson, Ames Laboratory Chief Research Officer and F. Wendell Miller Professor of Energy Science at Iowa State University’s department of Materials Science and Engineering said, “Through the mechanochemistry you create as many vacancies as you can in a powder, which increases the surface area, and the process yields 10 percent alane. Alane is light, when it gives up hydrogen and transforms to aluminum it becomes recyclable like aluminum cans, it’s under no pressure, and therefore is safe for vehicle applications. While 10 percent is not yet a commercially viable yield, the science here puts it within reach upon further research and development.”
The research was conducted by Ames Laboratory, Iowa State University, University of Illinois Urbana-Champaign, University of Wisconsin-Madison, and the University of Pittsburgh. The research is discussed in a paper published in ChemSusChem, “Towards Direct Synthesis of Alane: A Predicted Defect Mediated Pathway Confirmed Experimentally,” by Lin-Lin Wang, Aditi Herwadkar, Jason M. Reich, Duane D. Johnson, Stephen D. House, Pamela Peña-Martin, Angus A. Rockett, Ian M. Robertson, Shalabh Gupta, and Vitalij K. Pecharsky.
A 145,000 PSI pressure reduction will surely make a difference on how other researchers look at Alane. 5000 PSI is still about double say, heavy equipment, construction or farm equipment hydraulic pressures. There aren’t a lot of off the shelf materials to work with, the but oil and gas industry has technology at these pressures. On the other hand hydrogen, being the smallest atom, soaks into about everything, so the containment- storage issue remains here until the hydrogen is parked in the vacancies. Its looking like a potential solution now with problems common to most all hydrogen technology, and that is a breakthrough.