Technology
What is it?
Metals, such as magnesium, chemically bond with hydrogen gas to be transported as a metal hydride. When the hydrogen is required, heat is applied to release it from the metal. Intermetallic hydrides are a variation in which transition metals are present instead of main group metals.
Why is it important?
Metal hydrides offer storage at moderate pressure, retrieval at safe temperatures, and a higher hydrogen storage density than pressurised or liquefied hydrogen.
Characteristics
Characteristics – high temperature hydrides
- Volumetric hydrogen density: High (> 100 L/Kg)
- Gravimetric hydrogen density: Moderate to high (7 to 10 wt%)
- Hydrogenation and extraction conditions: ~100 to 500°C, or above to achieve hydrogen reversibility
- Storage conditions: Reversibility in some cases occurs only under high temperature and pressure conditions, e.g. Mg/MgH2 is 20 bar and 300°C but AlH3 is >100 C and > 1000 bar H2 pressure
- Hydrogenation/dehydrogenation energy efficiency: 80%
Characteristics – low temperature hydrides
- Volumetric hydrogen density: High (> 100 L/Kg)
- Gravimetric hydrogen density: Low (< 2wt%)
- Hydrogenation and extraction conditions: -10 to 50°C
- Storage conditions: Reversible at room temperature and reasonable hydrogen pressure conditions (e.g. TiFe and LaNi5 can absorb hydrogen at 30 bar and 25°C)
- Hydrogenation/dehydrogenation energy efficiency: 90%
Benefits
- Hydrogen release is endothermic and self-regulated, reducing risk of accidental explosion
- Lower pressures than pressurised gas and more moderate temperatures than liquefied hydrogen, leading to increased safety
- Higher hydrogen-storage density than pressurised or liquefied hydrogen156
- Low temperature hydrides have near-ambient operating pressure and temperature
- For room temperature hydrides, extremely long cycle life, up to 20,000 cycles in some cases
- Negligible self-discharge
- 90% round trip efficiency for room temperature hydrides
- Can be readily scaled to very large capacities for grid storage
- Suitable for hydrogen transport to fuelling stations
Limitations
- For high temperature hydrides, hydrogenation and hydrogen release occur at elevated temperatures, ranging from ~100-500°C. Light metal simple hydrides require high temperatures for rapid hydrogen release
- Note: Hydrides of very high hydrogen storage capacity (e.g. aluminium hydride, AlH3) are low TRL as they are not reversible for hydrogen storage. Room temperature hydrides of lower hydrogen capacity (< 2 wt% H2) are high TRL
RD&D priorities
- For high temperature hydrides, improve hydrogen sorption kinetics for fast and effective dissociation of hydrogen molecules3
- Improve energy density, cycle life and operating temperature
- Improve gravimetric hydrogen density
Known active organisations
- The Australian National University
- CSIRO
- Curtin University
- Deakin University
- Griffith University
- The University of New South Wales
- The University of Queensland
- The University of Technology Sydney