Scientists at the University of New South Wales (UNSW), Australia, are developing a novel way to store hydrogen that could help turn it into a viable portable fuel source. The research centers on using synthesized nanoparticles of the compound sodium borohydride (NaBH4 for those who love chemistry), which when encased inside nickel shells exhibits surprising and practical storage properties including the ability to reabsorb hydrogen and release it at much lower temperatures than previously observed, making it an attractive proposition for transport applications.
Hydrogen is a clean burning fuel that can be extracted from sources including natural gas, biomass, coal and water. One of the major problems in making it a viable alternative fuel is storage – the atoms are so tiny that they can easily escape from many kinds of containers. Also, hydrogen is more volatile than petrol. It can burn like blazes and can react badly to other substances. As no one wants to have a car that can burst into flames when you switch on the engine, this problem has drawn the attention of scientists around the world.
When researchers from the UNSW Materials Energy Research Laboratory synthesized nanoparticles of the sodium borohydride and encased these inside nickel shells, the findings took them by surprise. 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. As a result, there has been little focus on sodium borohydride.
The new findings indicate that by controlling the size and architecture of these structures, their properties can be made reversible. In other words, NaBH4 absorbs the hydrogen like a sponge and then releases it, making it useful for application in vehicles. In its bulk form, sodium borohydride requires temperatures above 550°C just to release hydrogen. It’s pretty much the same even on the nano-scale, but this core-shell nanostructure saw energy release happening at just 50°C, and significant release at 350°C.
Dr Kondo-Francois Aguey-Zinsou from the School of Chemical Engineering at UNSW says this is a real breakthrough and his team hopes to have it commercialized in three to five years’ time. “No one has ever tried to synthesize these particles at the nanoscale because they thought it was too difficult, and couldn’t be done," he said. "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.’’
The findings are published in the Journal ACS Nano.