European researchers have observed new phase transitions and complex behaviour in potential hydrogen storage materials. 

Despite the emergence of promising materials for hydrogen storage, no single one has all the properties required for safe and effective storage, according to Bjørn Hauback from the Institute for Energy Technology, Kjeller, Norway and colleagues. But their research, focusing on light-weight boron-based compounds, may change that. 

 

Understanding hydrogen uptake and release is vital to developing new storage materials © ORNL

 

To store hydrogen in liquid form, a temperature of 20 K is needed, so more attention has been devoted to storing hydrogen in solid form. More energy can be stored in the solids than in liquids of the same mass, but the poor energy density for solids compared to hydrocarbons means that larger storage tanks are needed, making transportation awkward. To solve this problem, attention has turned to the light-weight compounds magnesium and calcium borohydride (Mg(BH₄)₂ and Ca(BH₄)₂). Both have high hydrogen content, but little is known about their hydrogen uptake and release. To rectify this, Bjørn Hauback and his team studied these processes with in situ diffraction experiments. 

The studies revealed unexpectedly complex decomposition pathways. Several phase transitions occur, some of which had not been observed previously. The experiments help in understanding the phases occurring throughout the desorption process. 

'Such knowledge is crucial for further development of these compounds or similar materials for hydrogen storage,' said Hauback. As solids are the only materials that satisfy international targets for storage capacity, a lack of a breakthrough in this research could spell the end for the hydrogen economy. 

Standing in the way of this vision are many challenges. The perfect storage material needs to satisfy many requirements and Hauback predicted that nanoscience and nanotechnology will play an important role.

Elinor Richards