Hydrogen Storage Using Metal Hydrides

The urgency and imminent need for energy storage in the energy transition is the main driver for metal hydride-based hydrogen storage, solid-state hydrogen storage technologies that have higher volumetric densities than gaseous or liquid-state hydrogen storage. Magnesium and sodium aluminum hydrides are examples of metal hydrides that can store large amounts of hydrogen. This stored hydrogen is subsequently discharged either by heating these compounds directly, passing them through a catalyst, or combining them with water (hydrolysis). Metal hydrides are tunable, enabling them to be customized for different applications. Additionally, they are heat activated, which facilitates the use of waste heat emitted by thermal compressors. Furthermore, when hydrogen is stored in its solid state through metal hydrides, it does not need to be compressed or liquified.    

However, metal hydrides tend to be bulky, which limits their applicability. They also undergo mechanical wear due to the significant changes in volume they incur during the charging and discharging process. A complete metal hydride-based storage system additionally requires a heat transfer system and material modification for storing sufficient hydrogen, increasing the cost of the hydrogen storage system substantially compared to alternative storage technologies.

Potential for Metal Hydrides

Metal hydrides are applicable across stationary storage and mobility. They provide a viable solution to enable off-grid installations for power generation and energy storage (including mining operations in Australia). Smart grid projects also involve metal hydride-based storage, including the HyLab experiment, where an integrated energy system of a proton exchange membrane fuel-cell and a metal hydride tank are used for improving overall energy management. In terms of mobile applications, submarines present a prime end use where fuel cells work in conjunction with metal hydrides for propulsion. Railroads are another mobile application in which energy density is paramount. Energy in these applications is supplied to traction engines over long periods when the lines are not electrified.

GKN Powder Metallurgy and McPhy are commercially involved in deploying metal hydrides for hydrogen storage. GKN’s HY2 tanks are filled with compressed metal powder that, when brought in contact with hydrogen, bonds in a stable and dense way. These systems can store hydrogen for months and satisfy heat and electricity demand. France-based McPhy previously collaborated with Italy’s Enel to provide a magnesium hydride-based solid hydrogen storage system. The system was deployed with the objective of providing seasonal storage for renewable electricity generation. 

Outlook for Metal Hydrides

Extending changing energy policies and incentives to advanced but less market-mature technologies will provide the impetus needed for metal hydride hydrogen storage. As the demand for hydrogen storage technologies grows, given their versatility, metal hydrides will benefit from economies of scale that lead to cost reductions. Finally, the production of metal hydride storage, in contrast to alternate hydrogen storage technologies, can be significantly increased, making it a prime technology for meeting the rising demand for hydrogen storage.