Future technologies of the hydrogen economy
As the energy transition unfolds, it has become abundantly clear that the UK needs to develop suitable hydrogen storage solutions. Thanks to its clean burning capabilities and versatility as an energy carrier, hydrogen is an attractive solution for decarbonising hard-to-abate sectors, including heavy industry, chemical manufacturing, and long-haul transport.
While physical hydrogen storage methods such as compression and liquefaction are currently the most commercially viable options, there are a number of alternative storage technologies in development. Material-based and adsorption-based methods offer innovative approaches that may feature in the future hydrogen economy.
Material Based Hydrogen Storage
Material based hydrogen storage involves chemically bonding hydrogen with different materials to form stable compounds, allowing it to be stored in a denser and less reactive form. These methods fall into two primary categories: metal hydrides and chemical hydrogen carriers.
Metal Hydrides
Metal hydrides absorb hydrogen gas to form stable, solid compounds. When heated, the hydrogen is released and can be utilised.
Key Advantages:
- High volumetric hydrogen density: Metal hydrides can store more hydrogen per unit volume than compressed gas storage.
- Enhanced safety: Storing hydrogen in solid form reduces perceived risks associated with high-pressure systems and chemical reactivity.
Challenges:
- High release temperatures: Metal hydrides require extremely high temperatures to desorb hydrogen which is an energy intense process, and therefore costly.
- Weight limitations: Some hydrides are very heavy, which reduces reduces energy efficiency for transport applications.
- Cost: Some metals used in hydrides, such as titanium or vanadium, are expensive and not widely available.
Ongoing research is focused on developing lightweight, low-temperature hydrides that would improve their practicality for a wider range of uses.
Chemical Hydrogen Carriers
Chemical hydrogen carriers, store hydrogen in liquid form through chemical bonding. Common examples are compounds such as ammonia (NH₃) and liquid organic hydrogen carriers (LOHCs).
Key Advantages:
- Ambient storage conditions: These carriers eliminate the need for extreme pressures or cryogenic temperatures.
- Transport flexibility: Existing liquid fuel infrastructure can often be repurposed for their distribution.
- Energy dense: These compounds carry a significant amount of hydrogen. Ammonia (105kg per cubic metre) and LHOCs (54Kg per cubic meter) can compete with liquid hydrogen (73kg per cubic metre)
Challenges:
- Energy-intensive hydrogen release: Breaking the chemical bonds to release hydrogen is an energy intense process, so is not economically efficient at large scales.
- Safety concerns: Some chemical carriers are toxic and require
sspecialised handling.
Adsorption Based Hydrogen Storage
Adsorption-based storage involves capturing hydrogen molecules on the surface of porous materials, such as activated carbon, zeolites, and metal-organic frameworks (MOFs). This method relies on weak physical interactions rather than chemical bonds, offering a lightweight and scalable approach to hydrogen storage. This technology however is still in its developmental phase.
Carbon Based Materials
Activated carbons and graphene-based materials can adsorb hydrogen under high pressures and low temperatures.
Key Advantages:
- Scalability: These materials are relatively easy to manufacture and adapt for various applications.
- Lightweight design: Ideal for applications where weight is a concern, such as aerospace and automotive sectors.
Challenges:
- Low storage capacity: Hydrogen adsorption efficiency remains limited under ambient conditions.
- Temperature and pressure requirements: Effective storage typically requires low temperatures and/or high pressures.
Metal-Organic Frameworks (MOFs)
MOFs are crystalline structures made from metal ions and organic linkers, forming highly porous networks that can trap hydrogen molecules.
Key Advantages:
- Customisable structure: Theoretically, MOFs can be optimised for hydrogen storage by adjusting pore sizes and surface properties.
- High storage potential: MOFs offer impressive storage capacities at lower pressures compared to traditional physical storage.
Challenges:
- Cost and scalability: Producing MOFs on a commercial scale remains extremely expensive.
- Operational stability: Maintaining their performance over time requires further research and? development.
A notable innovation in this space comes from H2MOF, a California-based company developing advanced MOFs using nanotechnology. By increasing the surface area of these materials, they aim to achieve higher hydrogen storage densities at lower pressures (around 20 bar) and ambient temperatures, which would make the process safer and more cost-effective.
The Road Ahead: Hydrogen Storage for a Net-Zero Future
While material and adsorption based hydrogen storage methods present exciting opportunities for specific use cases, geological hydrogen storage remains the most efficient solution for large-scale, long-duration energy storage. Repurposing fossil fuel assets like depleted gas fields and salt caverns, proven storage solutions since the 1970s, provides a scalable and sustainable pathway for hydrogen storage in the green energy economy.
As the hydrogen economy evolves, it is likely that a combination of storage technologies will emerge, each tailored to specific applications. Continued investment in research and development will be essential to unlocking the full potential of these technologies.
Material and adsorption based hydrogen storage methods may one day become key players in the energy landscape, helping deliver the versatile hydrogen economy needed to meet the world’s decarbonisation goals.
