Material Insights · Understanding the Material World

Hydrogen storage: Science and technology

Squeeze it, chill it, bury it or bind it: four routes

What this tab covers The physics and chemistry: how the energy is stored, which materials it needs (scarcity, toxicity, recyclability) and what makes it age.

Hydrogen can be held physically (squeezed or chilled), underground in rock, or bound chemically to a metal or an organic liquid. Each route trades density against the energy spent getting hydrogen in and out.

Mechanism

Mixed

Compressed storage keeps hydrogen gas in steel or carbon-fibre tanks at 350 to 700 bar (1 bar is roughly atmospheric pressure). Liquid storage cools it to about minus 253 C. Salt caverns are large voids washed out of underground salt beds, 500 to 1,500 m deep, holding gas at up to about 200 bar. Depleted gas fields and aquifers store it in the pores of rock. Metal hydrides absorb hydrogen into a metal lattice, and liquid organic hydrogen carriers (LOHCs) such as benzyltoluene bond it chemically, releasing it again with heat at about 300 C.237

Salt cavern depth and pressure 500-1,500 m; up to about 200 bar7 Hydrogen per salt cavern 9 to 6,000 t7 LOHC (benzyltoluene) volumetric density about 54 kg H2 per m3 of carrier3 700 bar vehicle tank system, volumetric 0.86 kWh/L, about 26 kg H2 per m3 (calculated; 2023 status)2

Material scarcity and toxicity

Mixed

Hydrogen itself is non-toxic but highly flammable and leaks easily through small gaps. High-pressure tanks rely on carbon fibre, which is energy-intensive to make but not a critical mineral. Some room-temperature metal hydrides use alloys containing rare earths or titanium, which ties them to concentrated supply chains. Salt caverns need suitable salt geology, which is unevenly spread: of about 50 TWh of European salt cavern potential from repurposed gas sites, Germany holds about 39.5 TWh. Its maker describes the LOHC carrier as hardly flammable, with a flash point of 112.5 C and a hazard profile comparable to diesel rather than ammonia (company claim).35

European repurposable salt cavern H2 potential about 50 TWh, of which Germany 39.5 TWh (2021 estimate)5 LOHC-BT flash point 112.5 C3

Degradation and ageing

Mixed

Caverns and tanks do not fade like batteries, but they wear. Salt caverns can be very long-lived: a UK cavern built in 1972 is still in use. Hydrogen may react or mix in the store, so gas drawn from caverns may need drying and purification, and in porous fields microbes and minerals can consume or contaminate it, which is why depleted fields remain at pilot stage. Tanks suffer pressure-cycling fatigue and hydrogen embrittlement of metals. The LOHC maker says its carrier can be reused hundreds of times (company claim, no test data given).367

Oldest UK hydrogen salt cavern in service built 19727 LOHC carrier reuse hundreds of cycles (no exact count given)3

Hydrogen storage variants compared1356710

VariantTypical scaleEnergy to store or releaseMaturity
Compressed gas (350-700 bar)kg to tonnesabout 4% of hydrogen energy in theory for 700 bar; 5-20% at real stationsCommercial
Liquid hydrogen (minus 253 C)tonnes to thousands of tonnesabout 30-40% of hydrogen energy for liquefaction todayCommercial, niche
Salt caverns9-6,000 t per cavernmodest compression to about 200 barProven for static storage; fast cycling being demonstrated
Depleted gas fields and aquifersabout 215 TWh potential in Europe (with aquifers)compression plus cleaningPilots only
Metal hydridessmall (home) to medium (100 kWh to 100 MWh)heat needed to releaseNiche
LOHC (benzyltoluene)tonnes to thousands of tonnes per yearabout 11 kWh of heat per kg to release (about 33% of hydrogen energy, calculated)First commercial plants

Sources

  1. DOE Hydrogen Program Record 9013: Energy requirements for hydrogen gas compression and liquefaction US Department of Energy, 2009
  2. DOE Hydrogen Program Record 24006: Onboard Type IV compressed hydrogen storage system cost and performance status US Department of Energy, 2025
  3. LOHC brochure Hydrogenious LOHC Technologies, 2025
  4. H2 storage needs to exceed existing gas storage: GIE (reporting Gas Infrastructure Europe study) Argus Media, 2021
  5. Underground hydrogen storage: application of resource management (UNECE Resource Management Week) IEA Hydrogen Technology Collaboration Programme, 2021
  6. Hydrogen underground storage in salt caverns ENGIE Innovation, 2021
  7. Metal hydrides for hydrogen storage: identification and evaluation of stationary and transportation applications (Drawer, Lange, Kaltschmitt), Journal of Energy Storage 77, 109988 Elsevier (repository copy, Tecnalia), 2024