For the first time,
engineers at the University of New South Wales (UNSW) have demonstrated that
hydrogen can be released and reabsorbed from a promising storage material,
overcoming a major hurdle to its use as an alternative fuel source.

Researchers from the
Materials Energy Research Laboratory in nanoscale (MERLin) at UNSW have synthesized
nanoparticles of a commonly overlooked chemical compound called sodium
borohydride and encased these inside nickel shells.

Their “core-shell”
nanostructure has demonstrated remarkable hydrogen storage properties,
including the release of energy at much lower temperatures than previously
observed.

“No one has ever tried
to synthesize these particles at the nanoscale because they thought it was too
difficult, and couldn’t be done. We’re the first to do so, and demonstrate that
energy in the form of hydrogen can be stored with sodium borohydride at
practical temperatures and pressures,” says Kondo-Francois Aguey-Zinsou
from the School of Chemical Engineering at UNSW.

Considered a major a
fuel of the future, hydrogen could be used to power buildings, portable
electronics, and vehicles—but this application hinges on practical storage
technology.

Lightweight compounds
known as borohydrides (including lithium and sodium compounds) are known to be
effective storage materials, but it was believed that once the energy was
released it could not be reabsorbed—a critical limitation. This perceived “irreversibility” means there has been little focus on sodium borohydride.

However, the result, published in ACS Nano, demonstrates
for the first time that reversibility is indeed possible using a borohydride
material by itself and could herald significant advances in the design of novel
hydrogen storage materials.

“By controlling the
size and architecture of these structures we can tune their properties and make
them reversible—this means they can release and reabsorb hydrogen,”
says Aguey-Zinsou, lead author on the paper. “We now have a way to tap
into all these borohydride materials, which are particularly exciting for
application on vehicles because of their high hydrogen storage capacity.”

The researchers
observed remarkable improvements in the thermodynamic and kinetic properties of
their material. This means the chemical reactions needed to absorb and release
hydrogen occurred faster than previously studied materials, and at significantly
reduced temperatures—making possible application far more practical.

In its bulk form,
sodium borohydride requires temperatures above 550 C just to release hydrogen.
Even on the nanoscale the improvements were minimal. However, with their
core-shell nanostructure, the researchers saw initial energy release happening
at just 50 C, and significant release at 350 C.

“The new materials
that could be generated by this exciting strategy could provide practical
solutions to meet many of the energy targets set by the U.S. Department of
Energy,” says Aguey-Zinsou. “The key thing here is that we’ve opened the
doorway.”

Source: University of New South Wales