Hydrogen presents significant challenges when it comes to storage, given its molecular size and highly corrosive nature. A number of potential approaches are coming into view.
Leakage has certainly been a bête noire in the natural gas sector, and something that happens far more frequently than was assumed, as reports of recent years seem to confirm. It’s especially critical that such blunders don’t occur with hydrogen, whose propensity to combust is far more difficult to manage than with natural gas. True, hydrogen gas is extremely light, and prone to dispersing rapidly, producing dilute gas mixtures far less flammable than pure H2. But this might not be so reassuring in enclosed spaces.
It is also a more potent greenhouse gas than previously assumed, although these effects come about indirectly, when it interacts with other atmospheric gases to form methane and ozone. So the development of advanced storage technologies appears vital for the hydrogen economy to thrive.
Approaches to hydrogen storage tend to fall into one of two categories: those relying upon extremes of temperature or pressure storage (“physical-based” methods, as some put it), or those employing novel materials to store hydrogen either on the surface of a solid (by adsorption), or within the fabric of the solid (by absorption).
The latter, materials-based approaches are key to realizing hopes that hydrogen can be stored in a transportable format, without the complexity, cost and safety concerns of high-pressure gas or cryogenic storage.
The low density of hydrogen dictates that gas storage requires 300 to 700 times atmospheric pressure, while cryogenic storage requires temperatures of around –253°C. This obviously entails enormous energy demands. And since hydrogen molecules are so small, the possibility of leakage is difficult to fully eliminate.
MOFs take the pressure off…
Metal-organic frameworks offer one possibility for storing hydrogen within the fabric of a novel material, and this is the focus of an approach presented by start-up firm H2MOF, which – in the firm’s own description – uses nano-engineered materials to attract hydrogen molecules towards the nanoscale cavities of the material.
Heavyweight credentials support the firm’s R&D efforts, including Professor Sir Fraser Stoddart, a winner of the Nobel Prize in Chemistry for work developing molecular machines, and Omar Yaghi, a developer of the first MOFs. And the firm’s CEO, Samer Taha heads private equity firm Revonence Technologies, which
in turn has financed H2MOF, and the firm has a securely financed path up to commercialization, according to recent reports, removing the need to publicly clamour for attention and fnance.
H2MOF’s hydrogen fuel comes in the format of a grey powder, with advantages including significant storage density at pressure levels as low as 20 bar, which in turn means much higher safety levels, and seemingly high energy storage density at ambient temperature. The firm also cites fast hydrogen charge and discharge rates.
Organic chemistry
On the novel materials front, other possibilities include storing hydrogen in a liquid organic carrier, an approach under development with German firm Hydrogenious LOHC Technologies, which allows hydrogen to be stored in liquid form within an organic compound. In this case the hydrogen molecules are chemically bound to the LOHC via a catalytic reaction in a continuous process.
As hydrogen is required, it can be extracted from the material by dehydrogenation, which involves heating the material. However, heating is only required during this extraction, and not for storage.
The method can also claim safety and efficiency advances over high-pressure or cryogenic hydrogen storage, making it suitable for transportation and fuel-cell applications.
UK firm H2GO Power has focused on maximising the efficiency of hydrogen storage and release, using a sold-state form of storage. The firm’s website discusses the use of the approach with powering drones, providing a 3x increase in flight time compared to Li-ion batteries.
Graphene enters the fray
One would expect graphene to hold promise for hydrogen storage, although there have been obstacles to its use. In October, Graphmatech, a Swedish startup, launched a polymer-graphene composite, branded as AROS Polyamide-Graphene. It addresses many of the same core issues that restrict the use of physical storage methods for hydrogen.
The company has secured a grant of 10 million SEK (around £0.7 million) from the Swedish Energy Agency, which will support the development and scaling of the approach. AROS Polyamide-Graphene is said to combine the lightweight, flexible properties of polyamides (plastics) with the strength and impermeability of graphene. The result is a polymer said to be very well suited to hydrogen containment, particularly in type IV composite pressure vessels (CPVs), which are widely used for hydrogen storage and transport.
Graphmatech says the material overcomes a long-standing problem in the use of graphene for industrial applications: agglomeration. Graphene, while known for its strength, conductivity, and impermeability, tends to clump together when processed in large quantities, reducing its effectiveness. Graphmatech says it has developed a method to prevent this clumping, ensuring that the graphene is evenly distributed throughout the polymer matrix.
This in turn is germane to the material’s ability to prevent hydrogen from permeating through container walls. The combination of polyamide and graphene is said to improve the overall strength and durability of any container, enabling thinner, lighter designs that don’t compromise on safety.
The field certainly seems crowded, if anything, when it comes to predicting how exactly hydrogen will be stored in applications like future transport systems.
