An artist’s conception of the one-pot method for transforming ammonium borane into hydrogen fuel and an illustration of how the technology, which doesn’t produce greenhouse gasses, is good for the planet. Credit: Los Alamos National Laboratory |
Researchers have revealed a new single-stage method for recharging the
hydrogen storage compound ammonia borane. The breakthrough makes hydrogen a
more attractive fuel for vehicles and other transportation modes.
In an article appearing in Science, Los Alamos National Laboratory
(LANL) and Univ.
of Alabama researchers
working within the U.S. Department of Energy’s Chemical Hydrogen Storage Center
of Excellence describe a significant advance in hydrogen storage science.
Hydrogen is in many ways an ideal fuel. It possesses a high energy content
per unit mass when compared to petroleum, and it can be used to run a fuel
cell, which in turn can be used to power a very clean engine. On the down side,
H2 has a low energy content per unit volume versus petroleum. The
crux of the hydrogen issue has been how to get enough of the element on board a
vehicle to power it a reasonable distance.
Work at LANL and elsewhere has focused on chemical hydrides for storing
hydrogen, with one material in particular, ammonia borane, taking center stage.
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 U.S. Department of Energy.
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 burned. In other words, until
now, after hydrogen release, the ammonia borane couldn’t be recycled
efficiently enough.
The Science paper describes a simple scheme that regenerates ammonia
borane from a hydrogen depleted spent fuel form (called polyborazylene) back
into usable fuel via reactions taking place in a single container. 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. Regeneration takes place in a sealed pressure vessel
using hydrazine and liquid ammonia at 40 degrees Celsius and necessarily takes
place off-board a vehicle. The researchers envision vehicles with interchangeable
hydrogen storage tanks containing ammonia borane that are used, and sent back
to a factory for recharge.
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.
LANL researcher Dr. John Gordon, a corresponding author for the paper,
credits collaboration encouraged by the Center model with the breakthrough.
“Crucial predictive calculations carried out by Univ.
of Alabama Professor Dave Dixon’s
group guided the experimental work of the Los Alamos
team, which included researchers from both the Chemistry Division and the
Materials Physics and Applications Division at LANL,” Gordon said.
