EMPA: Optical hydrogen fuel gauge for metal hydride tanks

Licensing opportunity

Researchers at the Swiss Federal Laboratories for Materials Testing and Research have developed a hydrogen fuel gauge for metal hydride tanks, based on an optical fibre.

Hydrogen storage in metal hydride is a safe and reliable alternative to hydrogen stored in high-pressure vessels. A promising application of such storage devices is long-term energy storage, for example, stationary hydrogen storage for self-sufficient housing using hydrogen as a seasonal energy store, or for boats and submarines.

Such tanks will need to be equipped with a hydrogen fuel gauge, as an indicator of the actual amount of hydrogen stored in the metal hydride tank. Although there is a physical relation between the equilibrium pressure and the amount of hydrogen in a metal hydride, the pressure cannot be directly used to indicate the amount of hydrogen.

Thus, other methods to measure the amount of hydrogen in a tank are needed. At present this is done by making recordings of released and absorbed hydrogen by measuring the in- and outgoing hydrogen flux. However, leaks, the uncertainty of the flux measurement, and possible data storage losses may lead to the total amount of hydrogen stored being significantly different from the recorded figure.

As a result, researchers have developed the use of optical fibres to measure the change of optical properties of the surrounding hydrogen storage material through the optical near field effect.

To quantify the hydrogen content of the storage material, a long optical fibre is embedded in the hydrogen storage tank. The storage material sticks to the fibre and a change of the optical properties of the material causes a changed light attenuation, which is then correlated to the hydrogen content. The changes are averaged over the full length of the fibre, revealing the total hydrogen content of the tank

The gauge allows electronic charging level management for solid-state hydrogen storage in mobile and stationary applications, in particular for long-term storage.