Widespread use of hydrogen as an energy carrier is a key priority for the EU, in order to achieve its climate and energy transition targets. Hydrogen can be produced from renewable sources and stored as gas (compressed, cH2 or cryo-compressed, CcH2), liquid (LH2 at ~20K), chemically bound to liquid organic carriers, or solids or physically adsorbed onto porous materials. Chemical routes are associated with increased binding energies and require elaborate heat management schemes, while poor cyclability, slow kinetics and high desorption temperatures are important limitations from the application viewpoint. Physical processes like compression and liquefaction, although more advantageous, are energy intensive due to the required multi-stage compression (up e.g. to 700 bar) or cooling (down to ~20K). Moreover, these processes require the use of expensive composite or heavily thermally insulated bulky containers but they are also connected with critical safety considerations as they may involve very high pressures (cH2) or continuous H2 boil-off (LH2). The use of nanoporous (pore dimensions < 100 nm) materials for H2 storage is based on physical adsorption, involving weak physical gas-solid interactions. Gas adsorption is a spontaneous, exothermic, dynamic gas-solid equilibrium process favored at low temperatures and medium pressures (e.g. 77K, 100 bar). Although the search for effective H2 adsorbents has been ongoing for at least two decades, there are still significant challenges in developing and deploying nanoporous materials suitable for H2 storage.
Among the broad range of hydrogen adsorbents that have been investigated to date, metal-organic frameworks (MOFs) that are light-weight, highly ordered, porous crystals formed by combining inorganic building units (metal ions or clusters) and organic linkers, are considered to have notable advantages over other porous solids.
Despite intense research efforts worldwide, the development of actual MOF-based H2 storage systems and processes is an underdeveloped area of research, as there is a clear technological gap on how to identify suitable low-cost MOFs with the optimum combination of volumetric and gravimetric capacity but also negligible environmental footprint, and incorporate them into storage tanks. MOST-H2 directly addresses this challenge by mainly aiming at:
- Designing and developing new MOFs with usable H2 storage capacities of at least 10 wt% and 50 g/L below 100 bar.
- Developing a demonstration cryo-adsorption H2 storage system delivering up to 500 g of H2.
In this context, advanced synthetic strategies and sophisticated computational techniques, including machine learning, are being combined to deliver new, sustainable-by-design MOF adsorbents with suitable properties that can lead to more efficient, intrinsically safer and cost-effective storage solutions, compared to conventional hydrogen storage technologies. An important part of the project is also being devoted to designing, modeling and finally developing a cryo-adsorption storage tank, which will be properly tested in a TRL 5 environment. The project developments are also being coupled with full life cycle analysis and techno-economic assessment of the MOST-H2 technology to assess its potential with a view to selected end uses (rail and road applications).
