| Compressed hydrogen (350–700 bar) |
∼100, (15–40 kgH2 m−3) |
4–6 |
Mature technology, fast refuelling, simple system design |
High compression energy (7–15% of H2 energy), heavy tanks, safety concerns due to high pressure |
Fuel-cell vehicles, hydrogen refuelling stations, and short-term storage |
0.15–0.40 |
9 |
| Liquid hydrogen (LH2) |
∼100% H2; (70.8 kgH2 m−3) |
7–15 |
Highest purity, very high volumetric density |
Liquefaction energy (∼30–40% of H2 LHV), boil-off losses, cryogenic infrastructure |
Aerospace, long-distance transport, and large-scale storage |
1.5–4.3 |
8–9 |
| Metal hydrides (e.g., LaNi5, MgH2) |
1–7.6; (50–150 kgH2 m−3) |
1–4 |
High volumetric density, excellent safety, and reversible storage |
Heavy materials, slow kinetics, thermal management required, expensive alloys |
Stationary storage, backup power, portable systems |
0.5–2.5 |
5–8 |
| Adsorbent materials (MOFs, activated carbon, CNTs) |
∼4–8; (cryogenic); <2% at ambient conditions |
1–3 |
Fast adsorption/desorption, lightweight, reversible |
Low ambient-temperature capacity often requires cryogenic operation, high material cost |
Portable storage, research applications |
2.0–4.0 |
3–6 |
| Liquid organic hydrogen carriers (LOHCs) |
5–7%; (50–60 kgH2 m−3) |
4.5–6 |
Ambient storage and transport, existing liquid-fuel infrastructure, high safety |
Dehydrogenation requires catalysts and heat; hydrogen purification may be needed, with an energy penalty |
Large-scale transport, seasonal storage, and distributed hydrogen supply |
1.5–3.0 |
5–7 |
| Dibenzyltoluene (DBT/H18-DBT) |
6.2%; (57 kgH2 m−3) |
— |
|
— |
Low vapor pressure allows simple condensation; trace VOCs are easily removed via carbon filters |
— |
— |
| Benzyltoluene (BT/H12-BT) |
6.2%; (54 kgH2 m−3) |
|
|
|
Similar to DBT, low volatility makes separation easier, but high thermal stability limits the formation of side-product gases |
|
|
| Toluene/Methylcyclohexane (MCH) |
6.2%; (47 kgH2 m−3) |
|
|
|
High vapor pressure requires deep cooling and intense pressure swing adsorption (PSA) to meet fuel cell limits |
|
|
|
N-Ethylcarbazole (NEC/12H-NEC) |
5.8%; (54 kgH2 m−3) |
|
|
|
Very low volatility; highly pure H2, but requires scrubbing for trace nitrogen/amine degradation products |
|
|
| Naphthalene/Decalin |
7.3%; (65 kgH2 m−3) |
|
|
|
High capacity, but thermal cracking during release can produce trace amounts of methane, requiring additional purification |
|
|
| Benzene/Cyclohexane |
7.2%; (56 kgH2 m−3) |
|
|
|
High capacity, but benzene's extreme toxicity and high volatility require extensive, expensive purification efforts |
|
|
| Ammonia (NH3) |
17.6; (∼108 kgH2 m−3) |
13–15 |
High hydrogen density, mature transport infrastructure, and low liquefaction pressure |
Toxicity, cracking required before use, possible NOx formation |
International hydrogen transport, fertilizer and energy sectors |
3.0–4.0 |
8–9 |
| Synthetic fuels (e.g., methanol) |
Methanol: 12.5; (∼100 kgH2 m−3) |
10–11 |
Liquid at ambient conditions, existing infrastructure, and relatively easy handling |
CO2 emissions if fossil-derived, reforming required, CO purification needed |
Fuel distribution, marine transport, chemical feedstock |
2.0–2.5 |
7–9 |
