Metal Hydrides

Abstract

Metal hydrides are promising candidates for many stationary and mobile hydrogen storage applications. Presently, the most common use of metal hydrides is as anode material in commercial nickel-metal hydrides (Ni-MH) rechargeable batteries which have replaced conventional nickel-cadmium batteries in many applications. A wide variety of Ni-MH batteries are now on the market with cell sizes ranging from 30 mAh to 250 Ah [1,2]. Some other applications are: hydrogen compression [3], aircraft fire-detectors [4], isotope separation [5], and hydrogen getters for microelectronic packages. Hydride formation is also used in the HDDR process (hydrogenation-disproportionation-desorption-recombination) for the synthesis of magnetic materials such as Nd 2 Fe 14 B [6]. A striking application is as a component of cryocoolers for the ESA Planck mission [7]. Another exciting new application is the use of metal hydrides for switchable mirrors [8]. As we can see, metal hydrides have a wide range of applications. However, most research and development is targeted towards two applications: batteries and hydrogen storage. The former is now widely exploited but the latter is still facing many technical problems. The main advantages of storing hydrogen in a metal hydride are the high hydrogen volumetric densities (sometimes higher than in liquid hydrogen) and the possibility to absorb and desorb hydrogen with a small change in hydrogen pressure [9].The physics of hydrogen in elemental metals was reviewed at the end of the 1970s in thebooksHydrogeninMetals,volumesIandII [10,11].The1970s alsosawtheemergence of the important field of intermetallic compounds as hydride materials. An in-depth review of this field can be found in Hydrogen in Intermetallic Compounds volumes I, and II [12,13]. A review of the propertiesand applications of hydrogen in metals can befound in the third volume of Hydrogen in Metals [14]. The basic properties of the metal-hydrogen system are discussed from a fundamental point of view by Fukai [15]. Although initial studies on nanocrystalline and amorphous metal hydrides were initiated around the 1980s [16], the real emergence of nanocrystalline metal hydrides as a new class of Handbook of Hydrogen Storage. Edited by Michael Hirscher

Energetic evaluation of hydrogen storage in metal hydrides

“…However, the storage pressures are high, and the resulting system storage densities are still low . For metal hydride storage systems, hydrogen storage at ambient pressure is possible and remarkably higher volumetric system storage densities can be expected because of the high volumetric material storage densities . The liquefaction of hydrogen requires between 21 and 45 % of the lower heating value of hydrogen, depending mainly on the size of the liquefaction plant .…”

“…Exemplary pressure‐composition isotherms for temperatures T 1 and T 2 (left‐hand side) and resulting van't Hoff plot (right‐hand side). α and β represent the metal respectively hydride phase .…”

Hydrogen storage in filed magnesium

“…%) and relative low cost of magnesium. In opposition, the slow reaction kinetics and high temperatures needed for hydrogen absorption and release have been hindering its practical use [1][2][3]. This slow kinetics is especially important during the first absorption (activation) of hydrogen by magnesium.…”

“…One of the most challenging is to find a safe and feasible way of storing this gas for subsequent utilization in fuel cells [1][2]. Metal hydrides have been considered as interesting candidates for hydrogen storage, but the search for hydrides which fulfil all the technical requirements for hydrogen storage applications is far to be a simple task, remaining an open question so far.…”

“…These materials showed much faster reaction kinetics for hydrogen uptake and release at lower temperatures when compared to the polycrystalline counterparts [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. The investigated Mg nanocomposites consist of nanostructured magnesium and additives added during HEBM.…”