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| Ideal overall reaction scheme for AB (H3NBH3) regeneration from PB (“BNH”) with hydrazine (N2H4). Sutton et al. 1428 Click to enlarge. |
Los Alamos National Laboratory (LANL) and the University of Alabama (UA) researchers working within the US Department of Energy’s (DOE) Chemical Hydrogen Storage Center of Excellence have demonstrated a new single-stage method for recharging the hydrogen storage compound ammonia borane (H3N-BH3, AB).
The success of this particular advance builds on earlier work by members of this team (earlier post, Davis et al. 2009). The new development, described in a paper published in the journal Science, could make hydrogen a more attractive fuel for vehicles and other transportation modes.
The earlier work, described in a paper in Angewandte Chemie, discovered that a specific form of dehydrogenated fuel, called polyborazylene (PB), could be recycled with relative ease using modest energy input. Input from colleagues at Dow Chemical (also a Center Partner), indicated that an alternative approach to the work in the Angew. Chem. paper would be required if the ammonia borane recycle were to be feasible on a large scale.
The team developed a simple scheme that regenerates ammonia borane from a hydrogen-depleted form (called polyborazylene) back into usable fuel via reactions taking place in a single container.
We demonstrate that the spent fuel type derived from the removal of greater than two equivalents of H2 per molecule of AB (i.e., polyborazylene, PB) can be converted back to AB nearly quantitatively by 24-hour treatment with hydrazine (N2H4) in liquid ammonia (NH3) at 40 °C in a sealed pressure vessel.
—Sutton et al.
This one-pot method represents a significant step toward the practical use of hydrogen in vehicles by potentially reducing the expense and complexity of the recycle stage. The researchers envision vehicles with interchangeable hydrogen storage tanks containing ammonia borane that are used, and sent back to a factory for recharge.
Work at LANL and elsewhere has focused on chemical hydrides for storing hydrogen, with ammonia borane being of prime interest. Ammonia borane is attractive because its hydrogen storage capacity approaches 20% by weight—enough that it should, with appropriate engineering, permit hydrogen-fueled vehicles to go farther than 300 miles on a single tank, a benchmark set by the DOE.
Hydrogen release from ammonia borane has been well demonstrated, and its chief drawback to use has been the lack of energy-efficient methods to reintroduce hydrogen into the spent fuel once consumed. In other words, until now, after hydrogen release, the ammonia borane couldn’t be recycled efficiently enough.
The Chemical Hydrogen Storage Center of Excellence was one of three Center efforts funded by DOE. The other two focused on hydrogen sorption technologies and storage in metal hydrides. The Center of Excellence was a collaboration between Los Alamos, Pacific Northwest National Laboratory, and academic and industrial partners.
The Chemical Hydrogen Storage Center of Excellence, funded with $30 million, is a collaboration among multiple university and industrial partners across the country, including The University of Alabama, and with the Los Alamos National Laboratory in New Mexico and Pacific Northwest National Laboratory in Washington. Research for the project at UA, which was named a partner in the entity in 2004, is funded by some $2.2 million.
Resources
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Andrew D. Sutton, Anthony K. Burrell, David A. Dixon, Edward B. Garner III, John C. Gordon, Tessui Nakagawa, Kevin C. Ott, J. Pierce Robinson, and Monica Vasiliu (2011) Regeneration of Ammonia Borane Spent Fuel by Direct Reaction with Hydrazine and Liquid Ammonia. Science Vol. 331 no. 6023 pp. 1426-1429 doi: 10.1126/science.1199003
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Benjamin L. Davis, David A. Dixon, Edward B. Garner, John C. Gordon, Myrna H. Matus, Brian Scott and Frances H. Stephens (2009) Efficient Regeneration of Partially Spent Ammonia Borane Fuel. Angewandte Chemie Intl. Ed. 37, doi: 10.1002/anie.200900680