ABSTRACT
On the other hand, there is always a possibility for these target values to be reduced if the cost of fossil fuels grows abruptly due to economic or political reasons. Nevertheless, one should seriously perceive the above as a prime target at least for the next twenty years. Furthermore, one should not forget the irreversibility problem in hydrogen economy. For example, chemical generation of hydrogen from certain materials is highly effective and thermodynamically favorable [8]. However, the recycling of the resulting products back to their initial state might be complicated, energy intensive, and, consequently, energy and cost expensive. Nevertheless, it may happen that under sufficient market pressure, a particular kind of irreversibility (e.g., desorption is easy, but reabsorption is difficult) would then become acceptable. In such a case, a container of (obligatorily) cheap HSMs could be discarded without regeneration, similar to many existing single-use batteries [8]. The most promising modern methods of hydrogen storage based upon high technology and the knowledge of material science are characterized usually as physical or chemical. These methods provide the hydrogen storage via physical or chemical interaction of hydrogen with a number of materials. The fundamentals of these methods is strong interaction of either molecular or atomic hydrogen with materials of the storage medium [8]. Simple atomic mass-based calculations reveal that only the light (i.e., low atomic number) chemical elements can satisfy the criterion (i). Thus, the series of efficient HSMs can only be built from targeted chemical elements from an unfortunately short list: Li, Be, B, C, N, O, F, Na, Mg, Al, Si, and P. Furthermore, due to the toxicity or unfavorable chemical properties of hydrogen’s connections with Be, F, Si, and P, the list of chemical elements suitable for hydrogen storages must be reduced to only eight elements. Heavier ones may enter the multiple component system only as a low-abundant additive, presumably for fine-tuning of properties or as a catalyst [8]. In 2010, only two storage technologies were recognized as being susceptible to meet the targets of the Department of Energy of the United States: metal-organic framework, MOF-177 (see below), exceeds 2010 target for volumetric capacity, while cryo-compressed H2 exceeds more restrictive 2015 targets for both gravimetric and volumetric capacity [371].
