Hydrogen Storage Demystified: Gaseous, Liquid and Solid-State Solutions
Hydrogen has emerged as a cornerstone in the clean energy transition. It burns cleanly (only producing water vapour), can be made from renewable sources, and offers flexibility, as it can power vehicles, heat buildings, or store energy from intermittent sources like wind and solar.
Yet one of the biggest challenges remains: how do we store hydrogen safely, efficiently, and affordably?
There are four primary methods for storing hydrogen: as a compressed gas, as a cryogenic liquid, bound within a solid material (solid-state), or in liquid organic hydrogen carriers (LOHC), which are similar in concept to metal hydrides.
Let’s explore how they work, when they make sense, what’s new in research, and how the future might look.
1. Compressed Gaseous Hydrogen
How It Works
Compressed hydrogen is stored by squeezing the gas into strong pressure vessels – often at pressures of 350-700 bar (that’s about 350-700 times atmospheric pressure). Tanks are usually made of strong composite materials (such as carbon fibre over a liner) so they can safely hold the pressure without becoming too heavy.
Advantages
Simplicity and fast refuelling: It’s relatively easy to compress and fill tanks, and refuelling is quicker than cooling hydrogen to liquid or reworking solid materials.
Existing deployment: Many hydrogen fuel cell vehicles, buses, and industrial systems already use high-pressure gaseous hydrogen storage, making this the most mature method in real-world use.
Disadvantages
Energy cost: Compressing hydrogen to 700 bar uses up around 10-15% of the hydrogen’s own energy content.
Lower volumetric energy density: Even at high pressure, the energy per m3 is limited. Hydrogen is a light molecule, so even when compressed, it occupies more space than many fuels.
Tank weight and size: High-strength materials are required, which adds to the cost; additionally, tanks must be robust and engineered to meet safety standards.
Safety Considerations
Storing gas under high pressure poses obvious risks of leaks or structural failure.
To manage risks, systems typically include pressure relief valves, robust containment, leak detection, and good ventilation. Because hydrogen is lighter than air, it tends to disperse upward in the event of a leak, reducing the risk if buildings are well-designed and ignition sources are controlled.
2. Liquid Hydrogen Storage
How It Works
Liquefied hydrogen is cooled to approximately –252.8 °C, turning it into a liquid. This requires cryogenic technology: very well-insulated tanks (like massive vacuum-jacketed vessels) that limit heat entering the system so the hydrogen doesn’t boil away.
Advantages
Higher volumetric density compared to gas. Liquid hydrogen packs more mass of H₂ into a given volume than even high-pressure gaseous hydrogen.
Better suited for large-scale transport and long-range applications: Because more hydrogen can be stored per unit volume, liquid hydrogen is promising for heavy transport (ships, aircraft, and long-haul trucks), as well as for transporting hydrogen over long distances. It’s also essential in aerospace (such as rockets), where weight and volume are highly constrained.
Disadvantages
Energy-intensive liquefaction: Cooling hydrogen to a liquid requires a significant amount of energy, approximately 30-40% of the energy content of the hydrogen itself.
Boil-off losses: Even in perfectly insulated tanks, hydrogen gradually warms because some molecules change their nuclear spin state, a process that releases heat, causing hydrogen to revert to a gas and be vented or lost over the long term.
Cryogenic hazards: Extremely low temperatures pose a risk of cold burns and material embrittlement, necessitating more complex safety systems.
Safety Considerations
Handling liquid hydrogen requires mitigation of risks: materials must tolerate extreme cold without becoming brittle; personnel need protective gear; pressure relief systems are vital, because hydrogen expands enormously when warmed (moving from liquid to gas can increase volume nearly 800-fold).
Any boil-off must be managed (vented or reliquefied). Also, leakages of cold vapour can create invisible flammable clouds (though hydrogen’s properties again help, since hydrogen gas is very light and disperses upward).
Solid-state hydrogen storage refers to the binding of hydrogen within a solid material, either through absorption (forming a hydride with a metal or alloy) or adsorption (holding hydrogen on the surface of porous materials).
You “charge” the solid with hydrogen (often under some pressure or at elevated temperature), and then later “discharge” by heating or lowering pressure so hydrogen comes back out.
Examples include metal hydrides (e.g. AB5-type alloys, intermetallic alloys), porous materials (metal-organic frameworks, activated carbons), and chemical hydrides.
Advantages
Very high volumetric density: Some hydrides can store at densities comparable to or exceeding liquid hydrogen (kg of H₂ per litre of storage material), meaning a compact volume.
Lower pressure operation: Many hydrides require only moderate pressure to load hydrogen, and release may happen at moderate temperatures (depending on material). That reduces the stress and risk that come with high-pressure gas tanks.
Potential safety improvements: Because much of the hydrogen is “locked” in the solid form rather than being a free gas, the explosive risk is inherently lower. Also, storage can be more stable in many ambient conditions.
Thermodynamic regulation: Another advantage is that the process is governed by thermodynamics—using heating or cooling media rather than electricity when such media are available.
Disadvantages
Gravimetric penalty: The material storing the hydrogen (metals, alloys, adsorbents) adds a lot of weight. The overall system weight (material, container, and ancillary equipment) can reduce the effective hydrogen per kilogram.
Temperature/heat management needed: Heating is often required to release hydrogen, and cooling may be needed when absorbing hydrogen (since absorption can generate heat). Without proper heat exchange, performance suffers.
Slow kinetics: Absorbing/releasing hydrogen may be slow, especially for bulk materials. Nanostructuring, catalysts, and special material designs are being explored to speed this up.
Cost and durability: Many promising materials are expensive or use rare metals. Also, after many cycles (charging/discharging), materials may degrade (cracking, loss of ability to absorb hydrogen, contamination).
4. Comparing the Methods
The three storage technologies differ not only in how they hold hydrogen but also in their operating conditions, energy density, cost and safety profile.
Compressed gas systems store hydrogen at very high pressures—typically 350 to 700 bar—while maintaining ambient temperatures. Even at these pressures, the volumetric energy density is modest, roughly 5.6 megajoules per litre, so the tanks must be reasonably large and built from strong carbon-fibre composites with polymer liners.
The overall gravimetric capacity of such a system is around five per cent hydrogen by weight once the heavy tank is included. The energy needed to reach these pressures consumes about 10–15 per cent of the hydrogen’s own energy.
On the positive side, losses during storage are negligible and refuelling is quick, making this the most widely used method for fuel-cell cars, buses, and industrial cylinders.
Liquid hydrogen is stored at cryogenic temperatures, near –253 °C, and at only slight pressure. Cooling hydrogen to this point raises its density to roughly 8 megajoules per litre—about eight times that of room-temperature gas—while still being only a quarter of petrol’s density.
Liquefaction, however, is energy-hungry, typically absorbing 30–40 per cent of the hydrogen’s energy, and some inevitable boil-off occurs over time. Tanks require multilayer vacuum insulation and active venting to cope with expansion as liquid warms.
Despite these hurdles, liquid hydrogen is ideal when space and range are critical, such as in rocketry, long-haul trucking, and emerging hydrogen-powered aviation.
Solid-state storage relies on materials such as metal hydrides or advanced porous frameworks to absorb hydrogen at relatively low pressures, often well under 50 bar, and moderate temperatures that depend on the material.
Some of these solids can hold hydrogen with volumetric densities on par with liquid hydrogen—around 60 to 70 kilograms per cubic metre—but the host material adds weight, so total system hydrogen content is usually under five per cent by weight.
Energy efficiency depends on the amount of heating or cooling required to charge and discharge the material; some systems can utilise waste heat to offset this. Because the hydrogen is locked mainly within a solid, the explosion risk is lower; however, the materials themselves may be reactive and require sealed, well-engineered containers.
These contrasts illustrate why no single method is suitable for every need. Compressed gas dominates passenger transport thanks to fast refuelling and mature technology.
Liquid hydrogen offers the highest density for bulk transport and aerospace, but at the price of high energy input and complex safety systems. Solid-state storage promises exceptional safety and compactness for stationary applications and future vehicles once materials become lighter, cheaper and faster to cycle.
5. Efficiency, Costs and Environmental Trade-offs
It isn’t enough to look at storage alone. The real wisdom lies in weighing the amount of energy or cost lost in storing hydrogen, the duration it can be stored, and the sustainability of the materials and processes used.
Energy Losses: Compressing gas or liquefying hydrogen consumes energy. In many estimates, compressing to 700 bar costs ~10-15% of the hydrogen’s energy. Liquefaction can account for 30-40% of the total project cost, depending on the scale and technology employed. Solid materials avoid extreme compression or cooling, but require heat to release hydrogen; that heat must be available, and its source considered (waste heat helps).
Longevity and Losses Over Time: Liquid hydrogen suffers continuous boil-off; gaseous storage has almost no loss over time if sealed properly; solid storage may degrade chemically or physically over many cycles, resulting in a loss of capacity.
Cost of Materials and Infrastructure: High-pressure tanks, cryogenic insulation, hydride alloys, and catalysts, among other components, all contribute to the price. Scaling up helps reduce per-unit cost. Additionally, the use of rare or exotic materials can drive costs up while also facilitating sustainability.
Environmental and Safety Aspects: Materials for solid storage may involve mining metals; cryogenic cooling requires energy (which may come from non-renewables unless sourced carefully). Safety systems must be robust, regardless of the method.
6. When to Use Which?
Here are some general guidelines for selecting a storage method:
Vehicles / Mobile Use (cars, buses, trucks): Compressed gas is the current frontrunner, especially where refuelling infrastructure (stations with high-pressure compressors) is available. Liquid hydrogen could be used for long-haul, heavy transport once energy loss and safety issues are well-managed. Solid-state storage remains a viable future possibility if materials continue to improve, reducing weight and cost.
Stationary or Backup Power: Solid-state storage is particularly beneficial in this context because weight is less of a concern; safety and volume density are the more critical considerations. Additionally, being able to store hydrogen for extended periods without boil-off or pressure losses is also beneficial.
Large-scale Transportation / Aerospace: Liquid hydrogen is essential in rocketry today. For shipping or aviation, liquid or hybrid methods (liquid, cryogenic-compressed, or advanced hydrides) are being explored.
Renewables Integration: For capturing and storing intermittent energy sources (such as solar and wind), hydrogen can serve as a long-duration storage solution. Solid-state hydrides, underground storage of hydrogen gas, or carriers such as ammonia or liquid organic hydrogen carriers (LOHCs) may play a role in this context.
7. Recent & Emerging Innovations
Science and engineering continue to push boundaries:
High-Entropy Hydrides: Alloys combining multiple metals, designed to have favourable binding energies for hydrogen, enabling reversible absorption/desorption at near-ambient temperatures and moderate pressures [1].
Nanoconfinement: Embedding hydride particles in scaffolds (porous carbon, graphene, etc.) to reduce particle size, improve heat transfer, and facilitate faster hydrogen release [2].
“Zero Boil-Off” or Ultra-Low Boil-Off Tanks: Better insulations, active cooling systems, clever tank design to reduce energy lost through cryogenic boil-off in liquid hydrogen storage.
Hybrid Storage Concepts: Combining features of gas, liquid, and solid storage. For example, cryo-compressed hydrogen (moderately cold and under pressure) promises higher density with less extreme cooling; coupling storage with waste heat for release; and using metal hydride compressors to reduce reliance on mechanical compression [4].
Better Materials: Ongoing work into more affordable, abundant, robust hydride materials (magnesium-based, avoiding rare or expensive metals), and durable porous materials for adsorption, which offer good capacity without needing extreme pressures/temperatures.
Hydrogenera’s Metal Hydride-Based Hydrogen Storage Solutions
Hydrogenera offers a promising solid-state solution that leans heavily into metal hydrides. Our metal hydride containers store hydrogen by absorbing it into the crystal structure of metal alloys, enabling storage at low pressure and near room temperature.
Whether for remote stations, backup power, marine vessels, or grid support, Hydrogenera’s storage technology illustrates how solid-state storage can be safe, efficient, and deployable today.
References
High-Entropy Hydrides for Fast and Reversible Hydrogen Storage at Room Temperature: Binding-Energy Engineering via First-Principles Calculations and Experiments, Abbas Mohammadi et al., arXiv, 2023. Available at: https://arxiv.org/abs/2301.02811
MgH₂ nanoparticles confined in reduced graphene oxide pillared with organosilica: a novel type of hydrogen storage material, Feng Yan et al., arXiv, 2023. Available at: https://arxiv.org/abs/2308.10137
Metal Hydrides: Technoeconomic Insights into Metal Hydrides for some applications, X. Wang et al., 2025 (PMC). Available at:https://pubmed.ncbi.nlm.nih.gov/40179034/