Borohydride enables hydrogen ‘reversibility’ for the first time

Engineers at the University of New South Wales (UNSW) have demonstrated that hydrogen can be released and reabsorbed from sodium borohydride.

To achieve this, researchers from the Materials Energy Research Laboratory in nanoscale (MERLin) at UNSW synthesised nanoparticles of sodium borohydride and encased these inside nickel shells.

According to a statement, their ‘core-shell’ nanostructure has demonstrated hydrogen storage properties, including the release of energy at much lower temperatures than previously observed.

‘No one has ever tried to synthesise 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 to demonstrate that energy in the form of hydrogen can be stored with sodium borohydride at practical temperatures and pressures,’ said Dr Kondo-Francois Aguey-Zinsou from the School of Chemical Engineering at UNSW.

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

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. This perceived ‘irreversibility’ means there has been little focus on sodium borohydride.

However, the result, published last week in the journal ACS Nano, demonstrates for the first time that reversibility is 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,’ said 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 reportedly observed remarkable improvements in the thermodynamic and kinetic properties of their material, thus 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 higher than 550ºC 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 US Department of Energy,’ said Aguey-Zinsou.