w 26 | F Fooccuuss cnrs I international maaggaazziinnee manageable pressure levels, around a few dozen bars,” reports Gérald Pourcelly of the IEM1 in Montpellier. GOING SOLID The researchers first focused their efforts on porous carbon-based materials like activated charcoals, carbon nanotubes, graphene, and MOFs (metal-organic frameworks). “These solids offer a large surface area, on which the hydrogen molecules stick like water vapor condensing on a window,” explains Michel Latroche, director of the ICMPE.2 “Heating the material then makes it relatively easy to release the hydrogen and use it in a fuel cell.” The only, yet substantial problem is the requirement for very low temperatures, around –190°C. Researchers have 19 20 already managed to raise this temperature, but their results are still confined to the laboratory. META L STO RAGE Another kind of solid could hold greater promise for storage: metals, on which hydrogen is absorbed, forming compounds called hydrides. First discovered in the 1970s, these materials’ impressive storage capacities earned them the nickname of “hydrogen sponges.” Magnesium hydride is particularly promising, being abundant, inexpensive, and non-toxic, while carrying an exceptional hydrogen storage capacity (7.6 g per 100 g of hydride). © e . ler oy/CNRS Photothèque 21 © p hotos : 19-21-22 : c . fr ésil on/CNRS Photothèque 19 Melting of various elements (rare earths, magnesium, nickel, etc.) to produce a solid alloy used to store hydrogen. 20 “Pd@Carbon”, a hybrid material containing palladium nanoparticles (the dark spots), is studied as a potential hydrogen storage solution. 21 This tank, developed for storing hydrogen in solid form, can hold 7000 liters of the gas. 22 McPhy Energy’s disk contains 600 liters of hydrogen. MOF. Metal-organic framework, the term for solids made up of carbon and metals that can trap hydrogen in their nanometric pores. 20 nm 22
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