Australian Mines Limited advised positive progress from its Research and Development program targeting onboard Solid-State Hydrogen Storage solutions for light-duty vehicles. Development of practical, safe, cost-effective and efficient storage of a large amount of hydrogen in a small volume remains one of the fundamental challenges of the hydrogen economy. Currently, the two most common techniques used to store hydrogen are to compress it to a high pressure or to liquify it (liquefaction).

These storage methods require tanks and/or cooling equipment, which are bulky and heavy and are not expected to achieve the desired gravimetric and volumetric densities required to fulfill the United States Department of Energy targets for onboard Hydrogen Storage for Light-Duty Vehicles2. Solid-state hydrogen storage is considered to have the potential to meet the DOE targets. One of the most stringent DOE criteria for a hydrogen storage system is a target gravimetric capacity of 5.5 wt% of hydrogen by 2025.

In addition to the requirement of high gravimetric capacities, a desired system should exhibit a high volumetric capacity, a high rate of (de)hydrogenation at near-ambient temperatures, high reversibility (operational cycle life), high stability, and cost effectiveness. Metal Hydrides and Australian Mines R&D Program: High-capacity metal hydrides are expected to be very important for storage applications in the future hydrogen economy due to their exceptional attributes. The high gravimetric capacity of metal hydrides for hydrogen storage is one of the main advantages they have over the conventional mature compressed gas and liquid hydrogen storage methods.

MgH2, for example, has a gravimetric capacity of up to 7.6 wt% hydrogen. However, in practice it has not been possible to utilise the high gravimetric capacity of MgH2 for practical hydrogen storage technologies due to two major problems: the kinetics of hydrogen absorption and desorption in MgH2 is extremely slow occurring over the timescale of hours; and thermal stability of MgH2 is too high, requiring high temperatures to release hydrogen. To overcome these issues various researchers have focused on modifying Metal Hydride systems to improve hydrogen absorption and desorption properties, reaction rate kinetics and operating temperature.

While some success has been achieved with alloying and nano-crystallisation of MgH2 systems, results have been highly process dependant and have used processes that are difficult to apply to industrial scale manufacturing. It is Australian Mines' collaborative research and development (R&D) partnership with Amrita Centre for Research and Development, which is focused on both modifying Metal Hydride systems and the manufacturing process that has led to the development of the metal hydride MH-Oct22. The absorption and desorption capacities of MH-Oct22 at 350C were tested over four runs.

Figures 1a and 1b below show the second run which gave the best results. From the figures it can be observed that MH-Oct22 absorbs 5 wt% of hydrogen in 9.8 minutes and releases that same 5 wt % of hydrogen within 3.7 minutes. There are competing metal hydride hydrogen storage technologies.

One example is a thin film magnesium hydride storage technology being promoted by the company Plasma Kinetics3. Plasma Kinetics forms a thin film magnesium hydride into a disk resembling a CD that requires the use of a laser to extract the hydrogen. In contrast, Australian Mines' strategy is to prepare MH-Oct22 according to a newly developed process, which has been found to impart enhanced hydrogen storage properties.

It is envisaged that if an industrial scale technology is developed with this approach, it may allow the absorption and desorption using a gas phase chemical reactor. Although the results are promising, further development is required to achieve the 2025 DOE target for onboard Hydrogen Storage for Light-Duty Vehicles. Although MH-Oct22 exhibited hydrogen absorption and desorption at higher temperatures and pressures than the DOE operating temperature and pressure targets of 60C and 5-12 bar respectively, the company has several strategies that may improve reaction kinetics and operating temperatures and pressures.

Over the coming quarters the Company will continue to test these strategies to seek to develop new metal hydrides to improve on the performance of MH-Oct22. The Company will also commence a program of intellectual property protection.