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Metal hydride hydrogen storage. Metal hydrides, such as MgH 2, NaAlH 4, LiAlH 4, LiH, LaNi 5 H 6, TiFeH 2, ammonia borane, and palladium hydride represent sources of stored hydrogen. Again the persistent problems are the % weight of H 2 that they carry and the reversibility of the storage process. [16]
Electrode active areas of metal hydride fuel cells have been scaled up from 60 cm 2 to 250 cm 2, enabling systems to be scaled up to 500 Watts. [11] The scaling up of electrode active areas also provided capabilities to develop higher power fuel cell stacks, each with 1500 Watts of power. [6]
A hydride compressor is a hydrogen compressor based on metal hydrides with absorption of hydrogen at low pressure, releasing heat, and desorption of hydrogen at high pressure, absorbing heat, by raising the temperature with an external heat source like a heated waterbed or electric coil. [1] [2] [3] [4]
Classical transition metal hydride feature a single bond between the hydrogen centre and the transition metal. Some transition metal hydrides are acidic, e.g., HCo(CO) 4 and H 2 Fe(CO) 4. The anions potassium nonahydridorhenate [ReH 9] 2− and [FeH 6] 4− are examples from the growing collection of known molecular homoleptic metal hydrides. [16]
The hydrogen atoms occupy interstitial sites in palladium hydride. The H–H bond in H 2 is cleaved. The ratio in which H is absorbed on Pd is defined by = [] [].When Pd is brought into a H 2 environment with a pressure of 1 atm, the resulting concentration of H reaches x ≈ 0.7.
Some metal hydrides form when a metal complex is treated with hydrogen in the presence of a base. The reaction involves no changes in the oxidation state of the metal and can be viewed as splitting H 2 into hydride (which binds to the metal) and proton (which binds to the base). ML n x+ + base + H 2 ⇌ HML n (x-1)+ + Hbase +
Volumetric and gravimetric hydrogen storage densities of different hydrogen storage methods. Metal hydrides are represented with squares and complex hydrides with triangles (including LiAlH 4). Reported values for hydrides are excluding tank weight. DOE FreedomCAR targets are including tank weight.
A more energy efficient route to form lithium hydride powder is by ball milling lithium metal under high hydrogen pressure. A problem with this method is the cold welding of lithium metal due to the high ductility. By adding small amounts of lithium hydride powder the cold welding can be avoided. [7]