This article was built out of an Innovation Concierge request on solid-state hydrogen storage.

Problem Statement: A Darcy member from the power & utility industry asked us for an overview of solid state hydrogen storage.

The initial request desired information about:

• Different technological approaches in this space
• Technological/informational resources
• Major developmental players
• Cost bogies
• Scale/commercial status
• Application possibilities

The Innovation Concierge

There are four main hydrogen storage techniques: compressed storage, liquefaction, physical adsorption, and chemical absorption. Most current commercially available storage methods are based on compressed storage techniques. These, however, pose certain major limitations including serious and costly safety concerns when considering infrastructure buildout, large occupied space requirements, low storage capacities, necessary high pressure conditions, and, likely most daunting, high costs. Other commercialized methods include liquefaction, the storage of hydrogen as a liquid. Due to the phase properties of hydrogen (figure below), storing hydrogen as a liquid requires incredibly low temperatures, storage in high pressure tanks, a large volume/space requirement, has a high flammability range, and a fast boil-off rate without perfect tank infrastructure.

Due to the aforementioned issues with conventional physical (compressed and liquid) storage techniques, many are turning to opportunities in the fast developing world of solid state storage technologies, and not just for transportation applications. Solid state storage boasts much higher volumetric density, lower space requirements, and, for some systems, functionality under ambient conditions.

In previous Darcy coverage we created a framework that covers the entire Hydrogen value chain, from production, transportation and storage, to use. If you are interested in interacting with that framework please click the figure below. We will be expanding our coverage into other storage methods over the upcoming months, so keep checking back to keep up with new content.

The Hydrogen Storage Engineering Center of Excellence (HSECoE), as a part of the Hydrogen Materials Advanced Research Consortium (HYMARC), is a group conducting engineering research, development, and demonstration activities to address novel storage technologies’ engineering challenges. Recently, they developed models for several systems and published system projection graphs comparing them against 2020 DOE targets. HYMARC is a great group to follow to track progress as many of these technologies are accelerated into commercialization. They are a part of the U.S. Energy Department’s Energy Materials Network, which is a group focused on facilitating “stakeholder access to the national laboratories’ capabilities, tools, and expertise to accelerate the materials development cycle.”

The main targets of each technology’s success can be gauged off of desired applications, storage capacity levels, durability/operability, charging-discharging rate, dormancy, safety, hydrogen uptake per absolute weight, volume, and cost.

REVERSIBLE METAL HYDRIDE-BASED SYSTEMS

Many companies are developing technologies utilizing metal-hydrides (MH_x) due to their wide range of applications including electrochemical cycling, thermal storage, neutron moderation, heat pumps, and purification/separation. This method has advantages of high storage density, great stability, small space occupancy, and functions under ambient conditions. The main disadvantage is the high temperature/energy requirement for desorption due to strong bonding forces and slow kinetics. Much research and novel material development is going on right now and being scaled up to optimize desorption potential.

CHEMICAL STORAGE SYSTEMS

This category of hydrogen storage systems refers to covalently bound hydrogen (solid or liquid). Advantages and Disadvantages are similar to that of metal hydrides. Rehydrogentation processes need to be optimized through more materials research. Due to the incredibly high hydrogen capacity, ammonia borane and amide and amine compounds are still of interest, though the dehydrogenation reaction pathway is not straightforward.

HYDROGEN SORBENT SYSTEMS

Physisorption technology boasts advantages in price due to their ability to store hydrogen at room temperature and pressure. These materials are typically porous (for increased surface area), have light weight, high storage density (though not as high as metal hydrides and some chemical storage systems-disadvantage), superior reversibility and cycle stability compared to other solid state systems, and fast charging-discharging speed. Sorbents currently being utilized in this area include a range from coordination polymers to activated carbons and include zeolites, metal-organic frameworks (MOFs), covalent organic frameworks (COFs), and carbon materials (fullerenes, nanotubes, graphene), among others. Gravimetric adsorption is directly linked to surface area, so various geometries and production methods are incredibly important in optimizing the volumetric density and efficiency of ad/de-sorption. The main goals of current research and improvement in these systems are increasing the dihydrogen binding energies and improving the hydrogen volumetric capacity by optimizing pore size, pore volume, and surface area. Material densification is also being studied.

Depending on desired application, all of these solid state systems can have their advantages, and technology developers/researchers in the field are making incredibly fast progress in materials research and scaling.

TECHNICAL COMPARISON OF STORAGE METHODS

We have prepared this table based off of currently available literature in this area to compare the current methods in physical and chemical storage. Since this is an incredibly fast moving area within the academic research community, values may change, and we will update the information as new developments are made. Also important to note, these values within each category vary based on the material of choice. A great resource to gauge the functionality, compared to DOE goals, of individual materials can be found here.

COMPANIES OF INTEREST

The following list is anything but a complete catalogue of current companies working in this space, but some of those that Darcy found intriguing, either within the more immediately critical use-case of H₂ storage within the transportation space, or in residential, commercial, or other stationary applications. Keep a lookout for future Darcy coverage comparing innovators working in this space, and if you want a fast track of any of those listed below or others with basic storefronts on the platform, prior to our deep dives with each innovator, click on the lightning bolt next to their page, and we will fill out a storefront based on in depth desk research, and, of course, continue to pursue a conversation with the innovator.

• GKN Hydrogen
• McPhy
• GRZ Technologies
• H2Go Power
• Plasma Kinetics
• Lavo

Are you interested in seeing more Darcy coverage of solid-state hydrogen storage? If so, please comment below or send an email to lindseym@darcyparters.com.