Design a hydrogen-storage system that physisorbs H2 onto a metal-organic framework (MOF). Change the MOF, the temperature, the pressure and the loaded MOF mass to see the H2 uptake (wt% and volumetric density), the MOF mass required for a target H2 load, the achievement against DOE 2025 targets and the material cost — all in real time.
Parameters
MOF material
Sets the BET surface area, isotherm and cost
Storage pressure P
bar
Storage temperature T
K
77 K = liquid nitrogen, 298 K ≈ room temperature
MOF mass
kg
Target H₂ mass
kg
Target H2 mass for back-calculating the required MOF mass
MOF packing density ρ_MOF
kg/m³
Pelletizing and binders typically give 300-800
Results
—
MOF BET area (m²/g)
—
H₂ uptake (wt%)
—
Stored H₂ (kg)
—
Volumetric density (kg-H₂/m³)
—
Energy density (kWh/L)
—
Total cost (USD)
—
MOF crystal structure with H₂ adsorbed in pores
The green grid is the MOF pore network and the white dots are H₂ molecules. The temperature bar shows the current T and the gauge shows the current P.
Adsorption isotherm — wt% vs pressure (by temperature)
Linear interpolation between the measured 77 K and 298 K values; the pressure dependence is a Langmuir-type saturation curve with a characteristic pressure of 30 bar.
Volumetric energy density converted from the hydrogen heating value of 33 kWh/kg using the uptake and the MOF packing density.
Hydrogen storage — MOFs (metal-organic frameworks) and physisorption
🙋
I read that a MOF looks like "a crystal jungle gym". Is that really what they look like, and why does that help store hydrogen?
🎓
That mental image is right on. A MOF is a regular crystal built by connecting metal-ion clusters (Zn4O in MOF-5, for instance) and organic linkers (such as benzene dicarboxylic acid) as the nodes and edges — literally a jungle gym at the molecular scale. Most of its volume is empty, and the inner wall area of 1 g spread out covers a Tokyo Dome (a few thousand m²/g). Hydrogen molecules cling to that huge inner wall by physisorption (van der Waals forces), so the same tank stores more H2 than you would get by just compressing the gas.
🙋
Cool! So we just stuff more MOF in and the hydrogen tank gets smaller. With the default MOF-5 at 77 K and 70 bar I see wt = 6.41% — is that good compared with other ways of storing energy?
🎓
6.41 wt% means 5 kg of MOF holds 320 g of H2 — that is a solid number. For comparison, an empty tank at 70 bar stores about 5 g/L of hydrogen by volume, 700 bar compression reaches 39 g/L and liquid hydrogen 70 g/L. The tool gives 38.5 kg/m³ ≈ 38.5 g/L here. In other words, MOF + 70 bar matches "700 bar compression" in volumetric density at about one-tenth the pressure. That lets the carbon-fiber tank wall be thinner, which is a real weight saving.
🙋
That sounds great, but fuel-cell cars actually use 700 bar compression today. Why aren't MOFs commercial yet?
🎓
The biggest barrier is "no performance at room temperature". Push the temperature slider from 77 K (liquid nitrogen) up to 298 K and MOF-5 collapses from 7.1 wt% to 1.65 wt% — nowhere near the 5.5 wt% DOE target. That is because the physisorption energy (4-8 kJ/mol) is comparable to the room-temperature thermal energy kT ≈ 2.5 kJ/mol, so molecules leave the surface instantly. So putting today's MOFs in a fuel-cell car forces you to carry a liquid-nitrogen tank, and the system-level energy balance ends up worse than what it solves.
🙋
So what are researchers actually working on? NU-100 looks impressive at 9.95 wt%.
🎓
The main thrust is "raise the heat of adsorption to 15-20 kJ/mol so that 5 wt% survives at room temperature". The levers are (1) more open metal sites — the Cu²⁺ in HKUST-1 coordinates H2 directly and raises the adsorption heat, (2) tune the pore size to the 0.29 nm H2 molecule, (3) load Pt or Pd to spill hydrogen onto the framework. Super-high-area MOFs like NU-100 (6,100 m²/g) hold the 77 K world record, but at room temperature they are still only 1.85 wt%. So the field is shifting from "more surface area" to "stronger adsorption heat".
🙋
Cost is on my mind too. NU-100 at 500 $/kg — what does that work out to per car?
🎓
Say a fuel-cell car carries 5 kg of H2. With NU-100 you would need about 50 kg of MOF, so the material alone is 25,000 USD — about the price of a commercial vehicle. Not feasible. MOF-5 and HKUST-1, at 80-100 $/kg, come in at 4,000-5,000 USD, which is realistic. So the candidates that pair room-temperature performance with low cost (improved UiO-66 derivatives, for example) are the ones to watch. Cost is wired to the sliders here, so push the target H2 mass up and watch the MOF cost react.
Frequently Asked Questions
A MOF is a porous crystalline material built by linking metal-ion clusters and organic linkers into a regular framework. The internal surface area (BET) reaches 1,000 to 6,000 m²/g, among the largest known. H2 molecules physisorb onto this huge inner wall via van der Waals forces, so a tank packed with MOF holds more hydrogen than the same tank filled only with compressed gas. MOF-5, for example, adsorbs 7.1 wt% of H2 at 77 K and 100 bar, a few tens of percent more than just compressing gas into the same empty volume.
Physisorption relies on a weak attraction (heat of adsorption 4-8 kJ/mol). At higher temperatures, thermal motion strips the H2 molecules off the surface. MOF-5 drops from 7.1 wt% at 77 K to 1.65 wt% at 298 K. Reaching practical room-temperature performance requires a heat of adsorption of 15-20 kJ/mol, and research focuses on open metal sites (Cu in HKUST-1), tighter nanopores, and Pt/Pd doping. A practical 5 wt% MOF at room temperature does not yet exist, so today's designs combine MOFs with a cryogenic tank or with cold-climate / cold-chain logistics.
The U.S. Department of Energy targets for on-board hydrogen storage are 5.5 wt% gravimetric, 40 g/L volumetric, an operating range of -40 to 85 °C and a cost of about 9 $/kWh at the system level. This tool compares the MOF-only uptake and volumetric density against those targets. Both met = ok, only volumetric below = warn, gravimetric below = ng. System-level numbers (tank, insulation, valves) are typically 50-70% of the material-only values, so use the result as a material screening rather than a system specification.
70 MPa (700 bar) compression is the production technology in cars like the Toyota Mirai, with about 39 g/L volumetric density, but it requires expensive high-strength carbon-fiber tanks. Liquefaction at -253 °C reaches 70 g/L (the densest) but costs much energy to liquefy and suffers boil-off. MOFs at moderate pressure (30-100 bar) and moderate-low temperature (77-200 K) can approach liquid-like volumetric density while letting the tank wall be thinner. The practical obstacles are the energy budget for cooling and the share of system mass taken by insulation.
Real-World Applications
Fuel-cell vehicles and hydrogen-fuelled transport: Today's FCVs rely on 70 MPa compressed tanks, but combining a moderate pressure (30-70 bar) with a MOF fill lets the carbon-fiber wall be thinner and the system lighter. Because cryogenic operation is required, research focuses on long-haul trucks, trains and ships, where heavy insulation is acceptable. BMW iX5 Hydrogen has spawned MOF-tank concepts in which an improved HKUST-1 family operates at 100 bar and 150 K.
Stationary hydrogen storage and refuelling stations: In Power-to-Gas systems, surplus renewable electricity is turned into hydrogen and stored for later use in fuel cells or industry. Volumetric efficiency is critical, and a MOF-packed tank holds 2-3 times more H2 than a bare compressed tank of the same size, so it suits city-centre refuelling stations with tight footprints and storage paired with offshore wind farms. A German project, HYDROFILL, has tested 100 m³-scale tanks packed with MOF-177.
Hydrogen separation, purification and sensing: Beyond storage, the high selectivity of MOFs separates H2 from CO2, N2 and CH4 in membrane processes. UiO-66 and ZIF-8 give H2/CO2 selectivities of 10-30, putting them in line as PSA (pressure-swing adsorption) replacements. HKUST-1 also changes colour and conductivity with H2 concentration, and is already used in hydrogen sensors.
Catalyst supports and battery electrodes: MOF pores are excellent catalyst supports: dispersing Pt nanoparticles inside MOF pores cuts the Pt loading of fuel-cell electrodes to about a third. Conductively treated MOFs are also being studied as cathodes for metal-air batteries. The synthetic know-how built up for hydrogen storage is spilling over into neighbouring fields.
Common Misconceptions and Pitfalls
The first trap is to assume that "the larger the BET surface area, the more hydrogen the MOF stores". At 77 K the Chahine rule (wt% ≈ 0.0001 × BET) does hold, and that is why NU-100 and MOF-177 set the records. At room temperature, however, the correlation with BET is weak; what dominates is the heat of adsorption, which depends on pore size and chemical environment. Chasing only surface area without tuning pore size leaves you with a MOF that does nothing at room temperature. When evaluating a new MOF, always report not just the BET number but also the uptake at 298 K / 100 bar and the isosteric heat of adsorption.
The second pitfall is to read the tool's number as "system-level performance". The wt% and volumetric density here are for the MOF material alone. A real tank adds insulation, valves, heat exchangers and the tank itself, so the system wt% falls to 50-70% of the material-only value and the volumetric density to 60-80%. MOF-5 at 7 wt% becomes about 4 wt% at system level. To hit the DOE target, the material alone has to be 8 wt% or more, and the tank design has to be evaluated together.
Finally, do not compare physisorption MOFs head-to-head with chemical hydrogen storage (NaBH4, LiBH4, NH3BH3). Chemical hydrides reach 10-20 wt% but need 200-400 °C heat plus a catalyst to release the hydrogen, and the release reaction is irreversible (or needs a costly regeneration step). MOF physisorption is fully reversible and stable for more than 1,000 cycles but demands moderate-low temperature and moderate pressure. They are complementary rather than competing: pick by use case (mobile / stationary / long-term). Do not read this tool's output as "MOFs are worse than chemical hydrides".
How to Use
Select a MOF material (e.g., MOF-5, HKUST-1, or UiO-66) from the dropdown; each has distinct BET surface area (500–3000 m²/g) and H₂ binding energy.
Set storage pressure (1–100 bar) and temperature (77–298 K); lower temperatures and higher pressures increase physisorption capacity on the framework.
Enter MOF mass in kilograms and target H₂ mass; the simulator calculates uptake percentage, total stored H₂, volumetric density, and system cost based on current material pricing.
Review output metrics: BET area confirms surface properties, wt% uptake validates adsorption performance, and kg-H₂/m³ density determines tank footprint for automotive or stationary applications.
Worked Example
Design a H₂ storage tank for a fuel-cell vehicle. Select MOF-5 (BET = 2300 m²/g). Set pressure to 35 bar, temperature to 298 K, MOF mass to 40 kg, and target 4 kg H₂ storage. The simulator outputs: H₂ uptake ≈ 6.2 wt%, total stored H₂ = 2.48 kg, volumetric density ≈ 42 kg-H₂/m³, energy density ≈ 1.24 kWh/L, and material cost ≈ USD 8,000. If volumetric density is insufficient for range, increase pressure to 70 bar or reduce temperature to 77 K (cryogenic cooling), achieving 8.5 wt% uptake and 3.4 kg H₂ stored.
Practical Notes
MOF-5 and HKUST-1 excel at 77 K but require cryogenic systems (liquid nitrogen cost ~USD 0.30/liter); UiO-66 operates near ambient temperature with lower uptake (2–4 wt%) but eliminates cooling infrastructure.
Volumetric density must exceed 40 kg-H₂/m³ for automotive competitiveness; activate low-temperature operation or increase pressure beyond 50 bar if baseline MOF falls short.
Binding energy degrades after 1000+ adsorption/desorption cycles; factor replacement cost into long-term system economics, especially for stationary grid-storage applications requiring daily cycling.
Gravimetric energy density (kWh/L) depends on both H₂ content and MOF bulk density; denser materials like HKUST-1 (0.87 g/cm³) yield higher volumetric performance than aerogel MOFs (0.15 g/cm³).