Hydrogen storage, solid state

Volumetric versus mass densities achieved by various hydrogen-storage technologies. (Modified from Conte, M., Prosini, P., and Passerini, S., Mater. Sci. Eng. B Solid-State Mater. Adv. Technol., B108(l-2), 2-8, 2004.)... 

Storage of liquid hydrogen is achieved in large well-insulated tanks from which it is dispensed to liquid tankers for transport over the road. The use of hydrogen sensors (mostly flammable sensors) in and around such facilities is a common safety practice today. As hydrogen-specific sensors and solid-state sensors become more reliable, and if their cost is reduced they will replace the more common flammable gas sensors. 

During the course of the last century, it was realized that many properties of solids are controlled not so much by the chemical composition or the chemical bonds linking the constituent atoms in the crystal but by faults or defects in the structure. Over the course of time the subject has, if anything, increased in importance. Indeed, there is no aspect of the physics and chemistry of solids that is not decisively influenced by the defects that occur in the material under consideration. The whole of the modem silicon-based computer industry is founded upon the introduction of precise amounts of specific impurities into extremely pure crystals. Solid-state lasers function because of the activity of impurity atoms. Battery science, solid oxide fuel cells, hydrogen storage, displays, all rest upon an understanding of defects in the solid matrix. 

In practice, two basic bonding mechanisms are considered for hydrogen storage in solid-state materials ... 

Hydrogen can be stored as a gas, a cryogenic liquid, or, in addition, solid-state storage is also possible. A particular problem with liquid hydrogen is boiling off. As the liquid warms, boil off gas is released which must be vented from the storage tank. In confined spaces there is a risk of fire or explosion if contacted by a flame. 

R.A. Varin et al., Nanomaterials for Solid State Hydrogen Storage,... 

It is now appropriate to discuss solid state hydrogen storage in hydrides in the context of the targets shown in Table 1.2. 

Concurrent stream of the development of nanomaterials for solid-state hydrogen storage comes from century-old studies of porous materials for absorption of gasses, among them porous carbon phases, better known as activated carbon. Absorption of gases in those materials follows different principles from just discussed absorption in metals. Instead of chemisorption of gas into the crystalline structure of metals, it undergoes physisorption on crystalline surfaces and in the porous structure formed by crystals. The gases have also been known to be phy-sisorbed on fine carbon fibers. 

This brief history of century-old investigations toward hydrogen interaction with solid materials and nanomaterials brings us to the current state of affairs when the hydrogen storage for fuel cell systems still remains to be solved. Indeed, in the first decade of the new Millennium, and at the advent of the Hydrogen Economy, fuel cell stacks for use in mass transportation, like those developed by Ballard Power Systems based in Canada, are ready for mass commercialization. Also, hydrogen... 

Z.S. Wronski, Electrochemical storage of hydrogen in nanostructured solid-state hydrides and nanocarbons, International Conference on Processing and Fabrication of Advanced Materials- PFAM XII, Singapore (2004). Stallion Press, Singapore-London, pp. 275-287. 

The results of the research on LiAlH have been reviewed in a number of review articles (for reviews see [1-7]). This is the easily commercially available alanate with the highest theoretical storage capacity which equals 10.6 wt%H2 (Table 1.4 in Sect. 1.1). Such a high capacity makes it a potentially very attractive hydride for solid state hydrogen storage. 

In summary, neither MgCAlH ) nor CaCAlH ) seem to have a potential for further development as solid state hydrogen storage materials for mobile applications. Their storage properties seem not to be better than those of LiAlH or NaAlH. Nevertheless, they still deserve more research to arrive at the final verdict. 

H. Shao, H. Xu, Y. Wang, X. Li, Synthesis and hydrogen storage behavior of Mg-Co-H system at nanometer scale , J. Solid State Chem. 177 (2004) 3626-3632. 

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