The race is on to produce the first commercially available hydrogen car. With the depletion of fossil fuels an alternative is needed, and hydrogen, provided it can be produced without using fossil fuels, is a promising option. But there are challenges in both producing and storing hydrogen that must be overcome before commercial hydrogen cars become reality. 

The problem

One of the key requirements of materials for hydrogen storage is good cycling performance. Ti-V-Cr-Mo alloys have been proposed as a possible hydrogen storage system as they have the highest reversible storage capacity of materials of their type, but the capacity decreases with cycling. The exact location of hydrogen during cycling is key to understanding the loss in capacity. This is very difficult to achieve by X-ray diffraction as hydrogen is very light.

The solution

Neutrons scatter very strongly from hydrogen atoms but the Ti-Cr-V-Mo alloy developed by Toyota is almost totally invisible to neutrons. This meant neutron diffraction experiments could directly see the location of the hydrogen atoms within the solid. Dynamic experiments under high pressure to fill the alloy with hydrogen, and then remove the hydrogen by vacuum were carried out on the GEM neutron diffractometer and have unambiguously identified the cause of this loss of capacity.