New liquid can simplify hydrogen handling

New liquid can simplify hydrogen handling

Making a hydrogen-rich liquid that stays stable at normal temperatures could make hydrogen storage and transport much easier. In fact, there have been efforts to improve hydrogen storage by changing the chemical makeup of current storage materials or by adding substances that help hydrogen release more easily.

One promising area is deep eutectic solvents (DESs), which are mixtures that melt at lower temperatures than their ingredients. This is important for hydrogen storage because DESs can turn solid hydrogen-rich materials into easy-to-handle liquids at much lower temperatures. Until now, though, none of these DESs had used hydride components, which are especially rich in hydrogen and could open up new ways to store more hydrogen in liquid form.

Scientists from the groups of Professors Andreas Züttel at EPFL and Satoshi Horike at Kyoto University have developed the first example of a hydride-based DES: a transparent, stable hydrogen-rich liquid that stays liquid at room temperature. The new DES can contain up to 6.9% hydrogen by weight, exceeding several technical targets for hydrogen storage including those set for 2025 by the US Department of Energy.

To make the new DES, the researchers physically mixed ammonia borane and tetrabutylammonium borohydride in different amounts to determine which combination(s) would stay liquid at room temperature. The right ratio (between 50% and 80% ammonia borane) produced a stable liquid that stayed amorphous, meaning it didn’t form crystals again even at cold temperatures.

Using spectroscopy, the researchers confirmed that the molecules formed strong hydrogen bonds, breaking up their usual solid structure and keeping the mixture liquid down to minus 50°C. Tests showed the new liquid could release hydrogen when heated to just 60°C, much lower than most hydrogen-rich solids. This means hydrogen can be accessed more easily and efficiently, making storage and use much more practical for real-world applications.